The Nonthyroidal Illness Syndrome
Suzanne Myers Adler, MDa,b,*,
Leonard Wartofsky, MD, MACPa,b,c
aDepartment of Medicine, Washington Hospital Center, Room 2A-62,
110 Irving Street, NW, Washington, DC 20010, USA
bGeorgetown University School of Medicine, Building D, Suite 232,
4000 Reservoir Road, Washington, DC 20007, USA
cUniformed Services University of the Health Sciences, 4301 Jones Bridge Road,
Bethesda, MD 20814, USA
The evaluation of altered thyroid function parameters in systemic illness
lamic-pituitary-thyroid axis. The so-called ‘‘nonthyroidal illness syndrome,’’
also known as the low T3 syndrome or euthyroid sick syndrome, is not a true
clinical situations that commonly include a low serum triiodothyronine (T3),
normal to low thyroxine (T4), and a high reverse T3 (rT3). These typical
changes may be observed in up to 75% of hospitalized patients . We gener-
mone action at the cellular level because of alterations in intracellular thyroid
hormone uptake, receptor binding, and hormone binding to their serum
transport proteins in systemic illness [2–4]. Thyroid function abnormalities
can occur within hours of acuteillness, andthe magnitudeof these alterations
correlates with severity of disease with the lowest T3 andT4 values associated
with decreased survival. Although it has been concluded that the probability
predictor of survival [5–8], as are elevated rT3 and decreased T3/rT3 . This
during several clinical conditions and secondary to specific pharmacologic
* Corresponding author. Department of Medicine, Washington Hospital Center, Room
2A-62, 110 Irving Street, NW, Washington, DC 20010, USA.
E-mail address: firstname.lastname@example.org (S.M. Adler).
0889-8529/07/$ - see front matter ? 2007 Elsevier Inc. All rights reserved.
Endocrinol Metab Clin N Am
36 (2007) 657–672
Alterations of thyroid economy with nonthyroidal illness
Thyroid hormone parameters in nonthyroidal illness have been reviewed
in detail elsewhere . We provide a brief summary of the changes typically
Low serum T3 is the most common manifestation of altered thyroid
economy in nonthyroidal illness. The enzyme 5’-deiodinase catalyzes the
monodeiodination of approximately 35% to 40% of circulating T4 to pro-
duce the active hormone T3, thereby accounting for 80% to 90% of T3 in
the circulation; the remaining 10% to 20% of T3 is directly secreted by
the thyroid. Inhibition of 5’-deiodinase is believed to occur in nonthyroidal
illness, resulting in a decrease in T4 to T3 conversion in a variety of tissues
and hence low serum T3 concentrations .
Generally, decreases of serum T4 are seen in nonthyroidal illness and can
be due to hypothalamic-pituitary suppression, disordered iodine uptake,
abnormal peripheral metabolism, or decreased binding to carrier proteins
such as thyroid hormone binding globulin (TBG). Measurements of free
T4 are commonly within the normal reference range but may be low or
slightly increased depending upon the specific underlying disease process
Serum reverse triiodothyronine
rT3 is usually elevated in nonthyroidal illness. T4 to rT3 conversion by 5-
deiodinase is called the ‘‘inactivating pathway.’’ With impairment of 5’-de-
iodinase activity reducing metabolism of T4 by the activating pathway,
more T4 substrate is available for 5-deiodinase action via the inactivating
pathway and hence conversion to rT3. In addition, 5’-deiodinase ordinarily
converts rT3 to T2, and reduced activity of 5’-deiodinase slows clearance of
rT3, further elevating rT3 levels. In the setting of low serum T3 and T4 in
systemic illness, the differential diagnosis would include hypothyroidism.
Previously, measurements of rT3 were said to be useful to differentiate non-
thyroidal illness (with its high rT3) from hypothyroidism (which should be
associated with low rT3), but subsequent studies have shown that rT3 does
not accurately distinguish the two states .
ADLER & WARTOFSKY
TSH measurements most commonly within the normal reference range in
nonthyroidal illness has been the strongest held evidence that these patients
are ‘‘euthyroid’’ and is responsible for the continuing popularity of the des-
ignation ‘‘euthyroid sick syndrome.’’ Depending upon the etiology of the
underlying nonthyroid illness, TSH levels may be low, but only on rare oc-
casions are TSH levels undetectable due to nonthyroidal illness alone. TSH
may be transiently elevated even to greater than 20 mU/L during nonthyr-
oidal illness recovery .
Altered thyroid economy in specific clinical conditions
Starvation and fasting
The fasting state causes a down-regulation in the hypothalamic-pituitary-
thyroid axis and hence decreased thyroid hormone levels [14,15]. It may be
difficult to distinguish between the effects on thyroid function of a given sys-
temic illness versus those of the associated absolute or relative starvation be-
cause malnutrition is a component of many acute and chronic diseases. The
decreased serum T3 in starvation is hypothesized to reflect an attempt by the
organism to conserve energy by reducing metabolic expenditure. Investiga-
tive endeavors to restore serum T3 to the normal range during starvation
have resulted in evidence of increased muscle catabolism [16,17]. Therefore,
starvation-associated alterations in thyroid function different from those ob-
served in the fed state may not be abnormal but rather may represent appro-
priate alterations reflecting maintenance of homeostasis.
In the fasting state, substantial decreases in serum total and free T3 are
seen within 24 to 48 hours primarily due to the down-regulation of periph-
eral 5’-deiodination of T4 to T3. The increase in rT3 during fasting is mainly
due to decreased metabolic clearance of rT3 by 5’-deiodinase rather than in-
creased rT3 production from 5-deiodination of T4 to rT3 . On the other
hand, total T4 concentration may change little, and free T4 levels most com-
monly remain unchanged or may show slight increases due to fasting-in-
duced elevations in plasma free fatty acids (known to occur during
fasting), which inhibit hormone protein binding . Free T4 returns to nor-
mal within 2 weeks of continued fasting , although total T4 may exhibit
steady decreases corresponding to the fall in thyroid binding globulin seen
with prolonged minimal caloric intake . Long-term caloric restriction
in humans (range, 3–15 years) with adequate protein intake is associated
with a ‘‘chronic’’ low T3 syndrome .
Alterations in the regulation of thyroid hormone economy during starva-
tion occur not only peripherally via effects on deiodination and hormone
binding; changes also occur centrally. Reduced thyroidal secretion of thy-
roid hormones is thought to be due in part to suppression of TRH
NONTHYROIDAL ILLNESS SYNDROME
expression within the hypothalamic paraventricular nucleus leading to de-
creased stimulation of TSH production . In addition, altered glycosyla-
tion of newly synthesized TSH reduces TSH bioactivity and hence decreases
thyroid hormone secretion . Not only are TSH and TRH levels de-
creased with prolonged fasting, but the TSH response to TRH is also
blunted . A key factor causing a fall in TRH expression is a rapid de-
crease in the hormone leptin, which is known to be a major signaling protein
during the transition from the fed to the starved state . Leptin is ex-
pressed mostly in adipose cells, and a decrease in leptin increases appetite,
decreases energy expenditure, and modifies neuroendocrine function to fa-
vor survival during starvation . The mechanisms by which leptin mod-
ifies TRH expression or TSH secretion are unclear: Leptin may act
directly via leptin receptors on TRH neurons or indirectly via the hypotha-
lamic melanocortin pathway . Exogenous r-metHuLeptin administration
has been shown to prevent the fasting-induced changes of TSH but has had
no effect on the fasting-induced changes in T3 and rT3; this finding suggests
that leptin has no direct effect on deiodinase activity , but more studies
are needed to further elucidate these mechanisms.
Thyroid function is affected not only by caloric content but also by die-
tary composition. Reduced carbohydrate intake causes decreased T3, in-
creased rT3, and decreased thyroid binding globulin levels . Evidence
suggests that in fasting subjects, refeeding with 50 g of carbohydrate (200
kcal) can reverse fasting-induced changes in T3 and rT3 , but refeeding
with protein and fat cannot normalize T3 levels . Because 5’-deiodinase
contains selenium, a relationship between selenium deficiency and low T3
levels during fasting or nutritional deficiency had been surmised; however,
several prospective, placebo-controlled trials have concluded that low T3
levels during starvation and other severe illnesses are not directly related
to selenium deficiency .
The development of the nonthyroidal illness syndrome during infection
and sepsis involves central and peripheral mechanisms, including decreased
TSH secretion from the pituitary, reduced thyroidal secretion of T4 and T3,
and impaired peripheral T4 to T3 conversion. These changes contribute to
low T4, free T4, T3, and TSH and occur early in the course of sepsis. Be-
cause increased cytokine release is predominantly observed in sepsis as com-
pared with nonseptic diseases , attention has recently been focused on
the role of cytokines in the development of nonthyroidal illness syndrome
in the setting of sepsis and severe inflammatory states. Evidence suggests
that the cytokines interleukin (IL)-1b, soluble IL-2 receptor, IL-6, tumor ne-
crosis factor–a, and nuclear factor kB have roles in the direct suppression of
TSH in sepsis [31–34]. Nutritional deprivation during sepsis and severe ill-
ness also contributes to altered thyroidal economy in these settings .
ADLER & WARTOFSKY
Although earlier reports hypothesized that endogenous glucocorticoids sup-
pressed pituitary function, including TSH secretion in severe illness ,
more recently endogenous glucocorticoids were found to have little if any
contribution to the development of nonthyroidal illness syndrome .
The degree of thyroid function test alterations directly relates to infection
In most patients who have infections due to HIV, thyroid function pa-
rameters, including T3, free T4, and TSH, remain normal unless severe dis-
ease is present due to low CD4 cell counts [38–40]. One measurement that
may be altered is the serum TBG. Increases in TBG have been observed
in the HIV population for reasons that remain unclear but seem unrelated
to hepatic dysfunction. The mechanism might relate to altered TBG sialyla-
tion, which is known to decrease TBG clearance as seen in pregnancy and
other states of elevated serum estrogen levels . In one study of patients
who had Pneumocystis carinii pneumonia and AIDS, low serum T3 values
were associated with increased mortality. In addition, serum rT3 levels
were low in the outpatient setting and normalized after hospitalization for
severe illness. Unlike other causes of nonthyroidal illness syndrome, rT3
levels were not markedly elevated in this group of patients who had AIDS
. In one study of HIV-infected patients receiving highly active antiretro-
viral therapy, 23 out of 182 patients (12.6%) demonstrated lower free T4
and higher TSH levels, which is suggestive of subclinical or mild hypothy-
roidism . This could be due to immune reconstitution with the unmask-
ing of underlying Hashimoto disease that was previously quiescent.
Thyroid hormone is a key modulator of cardiovascular functions, includ-
ing heart rate, cardiac contractility, cardiac output, and peripheral vascular
resistance [44,45]. Alterations in thyroid function tests in cardiac disorders
are frequently observed with cardiac ischemia, congestive heart failure,
and after coronary artery bypass grafting. Decreased T3, increased rT3,
and decreased TSH and T4 have been found in acute myocardial infarction
and unstable angina, with the degree of T3 decrease and rT3 increase
proportional to the severity of disease. In these groups of patients, thyroid
function test changes were not affected by b-blockers or thrombolytics .
One prospective study investigating thyroid function in cardiac arrest found
total and free T3 to be significantly lower in patients after cardiac arrest
induced by acute coronary syndrome as compared with patients who had
acute uncomplicated myocardial infarction or healthy control subjects.
There were no significant differences between total T4, free T4, and TSH
levels among the groups. Much lower values of free and total T3, free and
total T4, and TSH were found in those who sustained prolonged cardiac ar-
rest than in those whose duration of cardiac arrest was shorter, and thyroid
function tests normalized at 2 months in those who survived .
NONTHYROIDAL ILLNESS SYNDROME
The prevalence of a nonthyroidal illness syndrome in congestive heart fail-
ure isapproximately 18% accordingto a recent prospective trial  andmay
be as high as 23% . Patients categorized as New York Heart Association
(NYHA) class III-IV are more likely to have thyroid function test abnormal-
NYHA class I-II heart failure. Deaths in heart failure patients who have non-
illness syndrome . In addition, so-called ‘‘subclinical’’ hypothyroidism
(defined as a TSH level above the upper limit of normal but with a normal
who have NYHA class II-III congestive heart failure . Low T3 has been
prospectively shown to be an independent predictor of mortality in hospital-
ized cardiac patients .
That impaired renal function can cause perturbations in thyroidal econ-
omy is not unexpected given the kidney’s role in the metabolism and excre-
tion of thyroid hormone. In the nephrotic syndrome characterized by
proteinuria exceeding 3 g daily, hypoalbuminemia, hyperlipidemia, and
edema, T3 levels are decreased. This was thought to be due to loss of
TBG in the urine along with other proteins ; however, TBG levels are
normal in many patients who have nephrotic syndrome and a preserved glo-
merular filtration rate (GFR) but are decreased if the degree of proteinuria
is high secondary to a severely reduced GFR . Serum rT3 levels are typ-
ically normal to low in nephrotic syndrome , in contrast to other forms
of nonthyroidal illness syndrome typically characterized by elevated rT3.
Glucocorticoids commonly given to treat nephrotic syndrome may compli-
cate the interpretation of thyroid function tests because they may lower TSH
secretion and decrease T4 to T3 conversion; in this setting, serum rT3 may
be normal to elevated. Free T4 and free T3 are typically normal in nephrotic
syndrome, and thyroid hormone supplementation should be reserved for pa-
tients who have at least mild TSH elevations as a consequence of large-scale
proteinuria and excess thyroid hormone wasting in the urine or with low se-
rum free T4 in the setting of glucocorticoid use.
End-stage renal disease (ESRD) alters the hypothalamic-pituitary-thyroid
hormone axis in addition to peripheral thyroid hormone metabolism .
ESRD leads to decreased total and free T3 because of reduced T4 to T3 con-
and thus cannot account for the low serum T3 [10,54]. Chronic metabolic ac-
idosis in ESRD may contribute to low free T3 levels , and low free T3 has
been prospectively shown to be an independent predictor of mortality in he-
modialysis patients . Another striking difference from other nonrenal
ADLER & WARTOFSKY
in the conversion of T4 to rT3 because rT3 levels are most commonly normal
in ESRD [57–60]. Although the clearance rate of serum rT3 is impaired in
ESRD, the apparent redistribution of rT3 from vascular to extravascular
spaces and enhanced intracellular entry of rT3 may account for failure to ob-
serve a further increase in serum rT3 levels [37,60]. Total and free T4 are gen-
erally slightlydecreased ornormal,but free T4may beincreased inthesetting
of heparin used for anticoagulation during hemodialysis because heparin is
known to inhibit T4 binding . TSH levels are generally normal in
ESRD, but TSH glycosylation is abnormal, which may affect the plasma
layed peak and prolonged return to baseline, perhaps due to reduced renal
clearance of TSH, TRH, or both [62–64]. Hemodialysis does not tend to nor-
malize the abnormal thyroid function parameters observed in ESRD, but
these alterations are largely reversed after renal transplant. Interpretation
of thyroid function test in the renal transplant population is complicated by
chronic posttransplant glucocorticoid use in many recipients, and persistent
attenuation of the response of TSH to TRH may be attributable to steroids,
especially if higher doses are used [10,53,54].
Normal liver function is important to thyroid metabolism because the
liver is the principal site of T4 to T3 conversion via 5’-deiodination, thyroid
hormone carrier protein (TBG and albumin) synthesis, T4 uptake, and sec-
ondary T4 and T3 release into the circulation. Abnormalities in thyroid
function tests vary based on the type and severity of hepatic dysfunction.
The abnormalities observed in cirrhosis, acute hepatitis, and chronic liver
disease are described below.
The most common thyroid function test abnormalities in cirrhosis are low
total T3, low free T3, and elevated rT3. The plasma T3:rT3 ratio is inversely
related to the severity of cirrhosis [65,66]. Free T4 may increase and total T4
may decrease secondary to changes in TBG and albumin binding properties
rather than normal TSH levels typically seen in nonthyroidal illness syn-
drome, theygenerallyremain clinicallyeuthyroidandhavenormaltodelayed
TSH and thyroid hormone responses to TRH injection [10,67].
The thyroid function test abnormalities that occur in acute hepatitis differ
markedly from those seen with other forms of liver disease and severe ill-
ness. Increased TBG is released from the liver as an acute-phase reactant
with concomitant elevations in serum total T3 and total T4 levels. Free
T4 and TSH are most commonly normal, but minimal elevations in rT3
and reductions in free T3 may be observed . Evidence suggests that
the rT3:T3 ratio may have value in assessing the severity of hepatitis and
the prognosis of patients who have fulminant hepatitis. For example, the
NONTHYROIDAL ILLNESS SYNDROME
rT3:T3 ratio quickly normalizes in survivors of fulminant hepatitis but does
not improve in nonsurvivors .
Although diseases such as chronic autoimmune hepatitis and primary bil-
iary cirrhosis are chronic diseases, their associated thyroid function test ab-
normalities more closely parallel those of acute hepatitis than those of
cirrhosis. Similar to acute hepatitis, serum TBG levels are elevated, with an
associated increase in total T4 and T3 concentrations. In contrast to cirrhosis
Because these forms of liver dysfunction have an autoimmune etiology, there
is a higher incidence of coexisting autoimmune thyroid disease that must be
distinguished from nonthyroidal illness syndrome. Up to 34% of patients
who have primary biliary cirrhosis have antithyroid microsomal antibodies,
and 20% have antithyroglobulin antibodies . Such patients are likely to
have Hashimoto thyroiditis and a propensity to develop subclinical or overt
hypothyroidism with thyroid function test abnormalities superimposed
upon those of the nonthyroidal illness syndrome. The degree of thyroid func-
tion abnormalities may not correlate with the severity of liver dysfunction in
chronic autoimmune hepatitis and primary biliary cirrhosis in contrast to the
stronger correlations in cirrhosis and acute hepatitis .
Effects of drugs on thyroid economy
Pharmacologic agents administered to patients who have systemic illness
may confound the interpretation of thyroid function tests. A complete re-
view of drug effects on the hypothalamic-pituitary-thyroid axis is beyond
the scope of this article and has been reviewed previously [72,73]. The fol-
lowing section highlights the alterations in thyroid function parameters sec-
ondary to drugs commonly used in severe systemic illness.
suppression of TSH secretion, down-regulation of T4 to T3 conversion by 5’-
deiodinase, and decrease of TBG concentration and hormone-binding capac-
ity . Together, these alterations result in low TSH, low T3, low T4, and
normal to slightly low free T4; these changes may be seen as soon as 24 to
36 hours after glucocorticoids are initiated [72,74–78].
Dopamine is administered intravenously in the intensive care setting for
its high-dose pressor effects and, at some clinical centers, for its low-dose re-
nal perfusion effects. Prolonged use of dopamine (ie, for several days) can
result in precipitous TSH suppression and hence low T4, free T4, T3, and
ADLER & WARTOFSKY
free T3, which may lead to secondary hypothyroidism with worsening prog-
nosis until thyroid hormone replacement is given [10,79].
Amiodarone, commonly administered for its antiarrhythmic effects, has
a high iodine content reported to be 37% . Amiodarone may increase
or decrease thyroid hormone secretion and inhibits T4 to T3 conversion
by 5’-deiodinase, resulting in decreased T3 and increased rT3 levels .
Amiodarone slows T4 metabolism, leading to T4 and free T4 elevations,
and may cause short-term TSH increases . Although the T4 effects
may persist, T3 and TSH generally normalize after several months on amio-
darone [37,81]. Most patients remain euthyroid on amiodarone, but the
drug causes hypothyroidism in 5% to 25% of patients (more common in re-
gions with adequate iodine intake) and hyperthyroidism in 2% to 10% of
patients (especially in iodine-deficient regions) .
At common therapeutic doses, furosemide has little if any effect on thy-
roid parameters. At higher doses that may be used during hospitalization for
aggressive diuresis (ie, O80 mg intravenously), furosemide causes a transient
elevation in free T4 and a decrease in T4 due to the displacement of T4 from
TBG. The magnitude of change depends on a number of factors including
serum concentrations of albumin, which also bind furosemide [72,82–84].
Salicylates cause a transient increase in free T4 due to inhibition of T3
and T4 binding to TBG in a similar manner to furosemide. This effect is
seen in high doses (ie, O2 g daily), and once a steady-state of the drug is
achieved, free T4 normalizes with a 20% to 30% decrease in T4 [72,85–87].
Phenytoin increases the rate of hepatic metabolism of T4 and T3 and may
cause decreases in free T4 and rT3 but with generally normal TSH . Free
T4 measurements by equilibrium dialysis suggest that free T4 continues to
be normal . The effects of phenytoin on T3 and free T3 are variable,
and these parameters may be depressed or remain normal in patients receiv-
ing this medication [88,89].
Propranolol may cause minimal inhibition of 5’-deiodinase, thereby de-
creasing T3 and increasing rT3 , but propranolol does not cause in-
creased thyroidal secretion .
NONTHYROIDAL ILLNESS SYNDROME
Iodine is a constituent of the intravenous contrast agents routinely used
for CT studies and cardiac catheterization procedures. Iodine acutely re-
duces thyroid hormone secretion and exacerbate hypothyroidism. Con-
versely, large iodine loads can precipitate thyrotoxicosis in patients who
have underlying autonomous thyroid function .
Thyroid hormone treatment during nonthyroidal illness
The commonly held notion that patients who have nonthyroidal illness
are euthyroid continues to be debated [1,5,91–97]. The metabolic state in
these patients has been deemed to be euthyroid based on generally normal
TSH and free T4 measurements. Changes in thyroidal economy may play
an adaptive role in times of stress, but consideration has also been given
to the possibility that patients who have nonthyroidal illness and low thy-
roid hormone levels may not respond with elevated TSH due to central hy-
pothyroidism from systemic illness. Because hypothyroidism exacerbates the
condition of many underlying disease processes, thyroid hormone adminis-
tration has been considered for treatment in patients who have nonthyroidal
illness. Because thyroid hormone is not without adverse effects, including
precipitating coronary ischemia, myocardial infarction, arrhythmia, or
death at supraphysiologic thyroid hormone levels [98,99], the issue of thy-
roid hormone treatment continues to be controversial.
Work in models involving organ donors who had suffered brain death
where thyroid hormonereplacement was givenin theorgan transplant setting
and benefits in cardiac inotropic function were observed [100,101] has led to
investigations with thyroid hormone administration in systemic illness. Dur-
ing coronary artery bypass grafting and in the immediate postoperative pe-
riod, total T3 decreases transiently. Several studies have investigated the use
thoughthis normalizes decreases in total T3, no significant effect onperioper-
ative morbidity and mortality has been found. Furthermore, although
lar resistance and improved cardiac output, there was no change in frequency
of arrhythmia, hemodynamic stability, duration of stay in the intensive care
unit, or inotropic drug requirements [102,103].
Evidence suggests that T3 administration may exert negative effects on
protein and fat metabolism [16,104,105], adversely affect catecholamine
levels found to increase as T3 and T4 levels decrease in critical illness
, and cause deleterious cardiac effects. Thyroid hormone replacement
during fasting , in patients who have ESRD who are on hemodialysis
, and in burn victims  has shown no beneficial effects. In a recent
study  involving patients who died in the intensive care unit, those who
received a combination of T4 and T3 replacement therapy had higher serum
ADLER & WARTOFSKY
T3 levels and higher levels of T3 in liver and skeletal muscle, with a twofold
greater increase in liver T3 than in serum T3. Patients who did not receive
thyroid hormone replacement had decreased levels of T4 and T3 in the liver
and skeletal muscle. Another study found that TRH infusion normalized pe-
ripheral thyroid hormone levels within 1 day in critically ill patients ;
these investigators hypothesize that this may be a safer alternative to thyroid
hormone administration with greater likelihood of avoiding supraphysio-
logic thyroid hormone levels.
If the clinician determines a trial of thyroid hormone replacement is war-
ranted in a patient who has deteriorating clinical status and thyroid function
test results suggestive of hypothyroidism, intravenous T3 administration is
preferred over T4 due to reduced 5’-deiodinase activity and hence decreased
conversion of T4 to metabolically active T3 in the sick patient. This was
confirmed in one study in the intensive care unit that administered intrave-
nous T4 sufficient to normalize T4 and free T4 and found that rT3 increased,
whereas T3 did not; these investigators observed no survival benefit between
those who did and did not receive thyroxine . The answer to the ques-
tion of whether or not thyroid hormone administration in nonthyroidal ill-
ness has a positive influence on outcome or prognosis in systemic illness is
likely to remain unanswered until studies conclusively indicate morbidity
and mortality benefits.
The evaluation of altered thyroid function parameters in systemic illness
and stress remains complex because changes occur at all levels of the hypo-
thalamic-pituitary-thyroid axis. Nonthyroidal illness syndrome is generally
characterized by low serum T3, normal free T4 and TSH, and elevated
rT3 values. Unique changes in thyroid function parameters are observed
in various clinical states, including starvation and fasting, cardiac disease,
renal disease, hepatic disease, and infection. Many pharmacologic agents
cause changes in thyroidal economy that can complicate the interpretation
of thyroid function parameters in systemic illness. Although alterations in
thyroid parameters may represent adaptive changes to conserve energy ex-
penditure by reducing metabolic activity, some argue that systemic illness
may induce a central hypothyroidism. The issue of thyroid hormone re-
placement remains controversial in the nonthyroidal illness syndrome.
 Wartofsky L. The low T3 or ‘‘sick euthyroid syndrome’’: update 1994. Endocr Rev 1994;3:
 Burman KD, Wartofsky L. Endocrine and metabolic dysfunction syndromes in the criti-
cally ill: thyroid function in the intensive care unit setting. Crit Care Clin 2001;17:43–57.
NONTHYROIDAL ILLNESS SYNDROME
 Ekins R. Measurement of free hormones in blood. Endocr Rev 1990;5:5–46.
 Sarne DH, Refetoff S. Measurement of thyroxine uptake from serum by cultured human
hepatocytes as an index of thyroidstatus: reducedthyroxine uptake from serum of patients
with nonthyroidal illness. J Clin Endocrinol Metab 1985;61:1046–52.
 De Groot L. Dangerous dogmas in medicine: the nonthyroidal illness syndrome. J Clin
Endocrinol Metab 1999;84:151–64.
 Maldonado LS,MurataGH,HershmanJM,et al.Dothyroidfunctiontestsindependently
predict survival in the critically ill? Thyroid 1992;2:119–23.
 Vaughan GM, Mason AD, McManus WF, et al. Alterations of mental status and thyroid
hormones after thermal injury. J Clin Endocrinol Metab 1985;60:1221–5.
to acute myocardial infarction. J Clin Invest 1985;8:507–11.
 Peeters RP, Wouters PR, van Toor H, et al. Serum rT3 and T3/rT3 are prognostic markers
in critically ill patients and are associated with post-mortem tissue deiodinase activities. J
Clin Endocrinol Metab 2005;90:4559–65.
the ‘‘euthyroid sick syndrome’’. Endocr Rev 1982;3:164–217.
 Kaptein EM, Grieb DA, Spencer C, et al. Thyroxine metabolism in the low thyroxine state
of critical nonthyroidal illnesses. J Clin Endocrinol Metab 1981;53:764–71.
 Chopra IJ. Simultaneous measurement of free thyroxine and free 3,5,3-triiodothyronine in
undiluted serum by direct equilibrium dialysis/radioimmunoassay: evidence that free triio-
dothyronine and free thyroxine are normal in many patients with the low triiodothyronine
syndrome. Thyroid 1998;8:249–57.
 Burmeister LA. ReverseT3 does notreliably differentiate hypothyroid sick syndrome from
euthyroid sick syndrome. Thyroid 1995;5:435–41.
 Suda AK, Pittman CS, Shimizu T, et al. The production and metabolism of 3,5,3-triiodo-
thyronine and 3,3,5-triiodothyronine in normal and fasting subjects. J Clin Endocrinol
 Blake NG, Eckland DJ, Foster OJ, et al. Inhibition of hypothalamic thyrotropin-releasing
hormone messenger ribonucleic acid during food deprivation. Endocrinology 1991;129:
 Gardner DF, Kaplan MM, Stanley CA, et al. Effect of triiodothyronine replacement n the
metabolic and pituitary responses to starvation. N Engl J Med 1979;300:579–84.
 Burman KD, Wartofsky L, Dinterman RE, et al. The effect of T3 and reverse T3 adminis-
tration on muscle protein catabolism during fasting as measured by 3-methylhistidine
excretion. Metabolism 1979;28:805–13.
 Lim CF, Doctor R, Visser TJ, et al. Inhibition of thyroxine transport into cultured rat
hepatocytes by serum of nonuremic critically ill patients: effects of bilirubin and non-
esterified fatty acids. J Clin Endocrinol Metab 1993;76:1165–72.
 Stockholm KH. Decrease in serum free triiodothyronine, thyroxine-binding globulin and
thyroxine-binding prealbumin whilst taking a very low-calorie diet. Int J Obes 1980;4:
protein and micronutrients on thyroid hormones. J Clin Endocrinol Metab 2006;91:
 Weintraub BD, Gesundheit N, Taylor T, et al. Effect of TRH on TSH glycosylation and
biological action. Ann NY Acad Sci 1989;553:205–13.
 Burman KD, Smallridge R, Osburne R, et al. Nature of suppressed TSH secretion during
undernutrition: effect of fasting and refeeding on TSH responses to prolonged TRH infu-
sions. Metabolism 1978;29:46–52.
 Ahima RS, Prabakaran D, Mantzoros C, et al. Role of leptin in the neuroendocrine
response to fasting. Nature 1996;382:250–2.
ADLER & WARTOFSKY
 Flier JS, Harris M, Hollenberg AN. Leptin, nutrition, and the thyroid: the why, the where-
fore, and the wiring. J Clin Invest 2000;105:859–61.
amo-pituitary thyroid axis and may mediate the effect of leptin. J Clin Invest 2000;105:
and metabolic adaptation to short-term starvation in healthy men. J Clin Invest 2003;111:
 Danforth E Jr, Burger AG. The impact of nutrition on thyroid hormone physiology and
action. Annu Rev Nutr 1989;9:201–27.
 Burman KD, Dimond RC, Harvey GS, et al. Glucose modulation of alterations in serum
iodothyronine concentrations induced by fasting. Metabolism 1979;28:291–9.
 Azizi F. Effect of dietary composition on fasting-induced changes in serum thyroid
hormones and thyrotropin. Metabolism 1978;27:935–42.
 Zimmerman MB, Kohrle J. The impact of iron and selenium deficiencies on iodine and
thyroid metabolism: biochemistry and relevance to public health. Thyroid 2002;12:
 Monig H, Arendt T, Meyer M, et al. Activation of the hypothalamo-pituitary-adrenal axis
in response to septic or non-septic disease: implications for the euthyroid sick syndrome.
Intensive Care Med 1999;25:1402–6.
 NagayaT, MiyukiF, Otsuka G, etal. A potentialrole ofactivatedNF-kBin the pathogen-
esis of euthyroid sick syndrome. J Clin Invest 2000;106:393–401.
 Reichlin S. Neuroendocrine-immune interactions. N Engl J Med 1993;329:1246–53.
 Lechan RM. Update on thyrotropin-releasing hormone. Thyroid Today 1993;16(1):1–11.
 Richmand DA, Molitch ME, O’Donnell TF. Altered thyroid hormone levels in bacterial
sepsis: the role of nutritional adequacy. Metabolism 1980;29:936–42.
 Kallner G, Ljunggren JG. The role of endogenous cortisol in patients with non-thyroidal
illness and decreased T3 levels. Acta Med Scand 1979;26:459–61.
 Cavalieri RR. The effects of disease and drugs on thyroid function tests. Med Clin North
 Grunfeld C, Pang M, Doerrier W, et al. Indices of thyroid function and weight loss in
human immunodeficiency virus infection and the acquired immunodeficiency syndrome.
 Hommes MJT, Romijn JA, Endert R, et al. Hypothyroid-like regulation of the pituitary
thyroid axis in stable human immunodeficiency virus infection. Metabolism 1993;42:
 Dobs AS, Dempsey MA, Ladenson PW, et al. Endocrine disorders in men infected with
human immunodeficiency virus. Am J Med 1988;84:611–6.
 Sellmeyer DE, Grunfeld C. Endocrine and metabolic disturbances in human immunodefi-
ciency virus infection and the acquired immune deficiency syndrome. Endocr Rev 1996;17:
 Lo Presti JS, Fried JC, Spencer CA, et al. Unique alterations of thyroid hormone indices in
the acquired immunodeficiency syndrome (AIDS). Ann Intern Med 1989;110:970–5.
 Madeddu G, Spanu A, Chessa F, et al. 2006 Thyroid function in human immunodeficiency
virus patients treated with highly active antiretroviral therapy (HAART): a longitudinal
study. Clin Endocrinol (Oxf) 2006;64:375–83.
 Polikar R, Burger AG, Scherrer U, et al. The thyroid and the heart. Circulation 1993;87:
 Klein I, Ojamaa K. Mechanisms of disease: thyroid hormone and the cardiovascular
system. N Engl J Med 2001;334:501–9.
 Pavlou HN, Kliridis PA, Panagiotopoulos AA, et al. Euthyroid sick syndrome in acute
ischemic syndromes. Angiology 2002;53:699–707.
NONTHYROIDAL ILLNESS SYNDROME
ities in cardiac arrest associated with acute coronary syndrome. Crit Care 2005;9:R416–24.
 Opasich C, Pacini F, Ambrosino N. Sick euthyroid syndrome in patients with moderate-
to-severe chronic heart failure. Eur Heart J 1996;17:1860–6.
 Manowitz NR, Mayor GH, Klepper MJ, et al. Subclinical hypothyroidism and euthyroid
sick syndrome in patientswith moderate-to-sever congestiveheartfailure. Am J Ther 1996;
 Iervasi G, Pingitore A, Landi P, et al. Low T3 syndrome: a strong prognostic predictor of
death in patients with heart disease. Circulation 2003;107:708–13.
 Afrasiabi MA, Vaziri ND, Gwinup G, et al. Thyroid function studies in the nephrotic
syndrome. Ann Intern Med 1979;90:335–8.
 Gavin LA, McMahon FA, Castle JN, et al. Alterations in serum thyroid hormones and
thyroxine-binding globulin in patients with nephrosis: qualitative aspects. J Clin Invest
 Kaptein EM. Thyroid hormone metabolism and thyroid disease in chronic renal failure.
Endocr Rev 1996;17:45–63.
pituitary-thyroidaxis andperipheralturnoverkineticsof thyroxineandtriiodothyronine. J
Clin Invest 1977;60:522–34.
 Wiederkehr MR, Kalogiros J, Krapf R. Correction of metabolic acidosis improves thyroid
and growth hormone axes in haemodialysis patients. Nephrol Dial Translpant 2004;19:
 Zoccali C, Mallamaci F, Tripepi G, et al. Low triiodothyronine and survival in end-stage
renal disease. Kidney Int 2006;70:523–8.
 Chopra IJ. An assessment of daily production and significance of thyroidal secretion of
3,3,3’,5’-triiodothyronine (reverse T3) in man. J Clin Invest 1976;58:32–40.
 Nicod P, Burger AG, Staheli V, et al. A radioimmunoassay for 3,3’,5’-triiodo-L-thyronine
in unextracted serum: method and clinical results. J Clin EndocrinolMetab 1976;48:823–9.
 Faber J, Heaf J, Kirkegaard C, et al. Simultaneous turnover studies of thyroxine, 3,3’,5’-
in chronic renal failure. J Clin Endocrinol Metab 1983;56:211–7.
 Kaptein EM, Feinstein E, Nicoloff JT, et al. Serum reverse triiodothyronine and thyroxine
kinetics in patients with chronic renal failure. J Clin Endocrinol Metab 1983;57:181–9.
 Silverberg DS, Ulan RA, Fawcett DM, et al. Effects of chronic hemodialysis on thyroid
function in chronic renal failure. Can Med Assoc J 1973;109:282–6.
 Ramirez G, O’Neill W, Jubiz W, et al. Thyroid dysfunction in uremia: evidence for thyroid
and hypophyseal abnormalities. Ann Intern Med 1976;84:672–6.
 Czernichow P, Dauzet MC, Broyer M, et al. Abnormal TSH, PRL, and GH response
to TSH releasing factor in chronic renal failure. J Clin Endocrinol Metab 1976;43:
 Duntas L, Wolf CF, Keck FS, et al. Thyrotropin-releasing hormone: pharmacokinetic and
pharmacodynamic properties in chronic renal failure. Clin Nephrol 1992;38:214–8.
 Guven K, Keletimur F, Yucesoy M. Thyroid function tests in non-alcoholic cirrhotic
patients with hepatic encephalopathy. Eur J Med 1993;2:83–5.
 Malik R, Hodgson H. The relationship between the thyroid gland and the liver. Q J Med
 Borzio M, Caldara R, Borzio F, et al. Thyroid function tests in chronic liver disease:
evidence for multiple abnormalities despite clinical euthyroidism. Gut 1983;24:631–6.
 Gardner DF, Carithers RL, Galen EA, et al. Thyroid function tests in patients with acute
and resolved hepatitis B infection. Ann Intern Med 1982;96:450–2.
 Kano T, Kojima T, Takahashi T, et al. Serum thyroid hormone levels in patients with
fulminant hepatitis: usefulness of rT3 and the rT3/T3 ratio as prognostic indices. Gastro-
enterol Jpn 1987;22:344–53.
ADLER & WARTOFSKY
 Schussler GC, Schaffner F, Korn F. Increased serum thyroid hormone binding and
decreased free hormone in chronic active liver disease. N Engl J Med 1978;299:510–5.
 Elta GH, Sepersky RA, Goldberg MJ, et al. Increased incidence of hypothyroidism in
primary biliary cirrhosis. Dig Dis Sci 1983;28:971–5.
 Surks MI, Sievert R. Drugs and thyroid function. NEJM 1995;333:1688–94.
 Cavalieri RR, Pitt-Rivers R. The effect of drugs on the distribution and metabolism of
thyroid hormone. Pharmacol Rev 1981;33:55–80.
 Chopra IJ, Williams DE, Orgiazzi J, et al. Opposite effects of dexamethasone on serum
concentrations of 3,3’,5’-triiodothyronine (reverse T3) and 3,3’5-triiodothyronine (T3).
J Clin Endocrinol Metab 1975;41:911–20.
 Duick DS, Warren DW, Nicoloff JT, et al. Effect of single dose dexamethasone on the
concentration of serumtriiodothyroninein man.J ClinEndocrinolMetab1974;39:1151–4.
 Gamstedt A, Jarnerot G, Kagedal B. Dose related effects of betamethasone on iodothyro-
nines and thyroid hormone-binding proteins in serum. Acta Endocrinol (Copenh) 1981;96:
 DeGrootLJ, HoyeK. Dexamethasonesuppressionof serumT3andT4. J ClinEndocrinol
 Lo Presti JS, Eigen A, Kaptein E, et al. Alterations in 3,3’,5’-triiodothyronine metabolism
in response to propylthiouracil, dexamethasone, and thyroxine administration in man.
J Clin Invest 1989;84:1650–6.
 Heinen E, Herrmann J, Konigshausen T, et al. Secondary hypothyroidism in severe non-
thyroidal illness? Horm Metab Res 1981;13:284–8.
 Melmed S, Nademance K, Reed AW, et al. Hyperthyroxinemia with bradycardia and
normal thyrotropin secretion after chronic amiodarone administration. J Clin Endocrinol
hormone levels and thyroid function. Am J Med 1985;78:443–50.
 Newnham HH, Hamblin PS, Long F, et al. Effect of oral furosemide on diagnostic indices
of thyroid function. Clin Endocrinol (Oxf) 1987;26:423–31.
 Stockigt JR, Lim CF, Barlow JW, et al. Interaction of furosemide with serum thyroxine
binding sites: in vivo and in vitro studies and comparison with other inhibitors. J Clin En-
docrinol Metab 1985;60:1025–31.
 StockigtJR,ToplissDJ.Assessment of thyroidfunctionduringhigh-dosefurosemidether-
apy. Arch Intern Med 1989;149:973.
 Larsen PR. Salicylate-induced increases in free triiodothyronine in human serum: evidence
of inhibition of triiodothyronine binding to thyroxine-binding-globulin and thyroxine-
binding prealbumin. J Clin Invest 1972;51:1125–34.
 Faber J, Waetjen I, Siersbaek-Nielson K. Free thyroxine measured in undiluted serum by
dialysis and ultrafiltration: effects of non-thyroidal illness and an acute load of salicylate of
heparin. Clin Chim Acta 1993;223:159–67.
 Bishnoi A, Carlson HE, Gruber BL, et al. Effects of commonly prescribed nonsteroidal
anti-inflammatory drugs on thyroid hormone measurements. Am J Med 1994;96:235–8.
 Smith PJ, Surks MI. Multiple effects of 5,5-diphenylhydantoin on the thyroid hormone
system. Endocr Rev 1984;5:514–24.
 Cavalieri RR, Gavin LA, Wallace A, et al. Serum thyroxine, free T4, triiodothyronine and
reverse-T3 in diphenylhydantoin-treated patients. Metabolism 1979;28:1161–5.
 Wartofsky L, Dimond RC, Noel GL, et al. Failure of propranolol to alter thyroid iodine
release, thyroxine turnover, or the TSH and PRL response to TRH in patients with
thyrotoxicosis. J Clin Endocrinol Metab 1975;41:485–90.
 Utiger RD. Altered thyroid function in nonthyroidal illness and surgery: to treat or not to
treat? N Engl J Med 1995;333:1562–3.
 Chopra IJ. Euthyroid sick syndrome: is it a misnomer? J Clin Endocrinol Metab 1997;82:
NONTHYROIDAL ILLNESS SYNDROME
 Wartofsky L, Burman KD, Ringel MD. Trading one ‘‘dangerous dogma’’ for another?
Thyroid hormone treatment of the ‘‘euthyroid sick syndrome’’. J Clin Endocrinol Metab
 De Groot L. Dangerous dogmas in medicine: author’s response. J Clin Endocrinol Metab
 Van den Berghe G. Euthyroid sick syndrome. Curr Opin Anaesthesiol 2000;13:89–91.
patients with thyroid hormone. Best Pract Res Clin Endocrinol Metab 2001;15:465–78.
thyroid hormone treatment? J Endocrinol Invest 2003;26:1174–9.
and shock following excess thyroid administration in a woman with normal coronary
arteries. Arch Intern Med 1988;148:1450–3.
 Bhasin N, Wallace W, Lawrence JB, et al. Sudden death associated with thyroid hormone
abuse. Am J Med 1981;71:887–90.
 Novitzky D. Heart transplantation, euthyroid sick syndrome, and triiodothyronine
replacement. J Heart Lung Transplant 1992;11:S196–8.
 Yokoyama Y, Novitzky D, Deal MT, et al. Facilitated recovery of cardiac performance by
triiodothyronine following a transient ischemic insult. Cardiology 1992;81:34–45.
 Bennett-Guerrero E, Jimenez JL, White WD, et al. Cardiovascular effects of intravenous
triiodothyronine in patients undergoing coronary artery bypass graft surgery: a random-
ized, double-blind, placebo-controlled trial. JAMA 1996;275:687–92.
 Klemperer JD, Klein I, Gomez M, et al. Thyroid hormone treatment after coronary-artery
bypass surgery. NEJM 1995;333:1522–7.
 Lim VS, Flanigan MJ, Zavala DC, et al. Protective adaptation of low serum triiodothyro-
nine in patients with chronic renal failure. Kidney Int 1985;28:541–9.
 Axelrod L, Halter JB, Cooper DS, et al. Hormone levels and fuel flow in patients with
weight loss and lung cancer: evidence for excessive metabolic expenditure and for an adap-
tive response mediated by a reduced level of 3,5,3’-triiodothyronine. Metabolism 1983;32:
 Madsen M, Smeds S, Lennquist S. Relationship between thyroid hormone and catechol-
amines in experimental trauma. Acta Chir Scand 1986;152:413–9.
 Lim VS, Tsalikian E, Flanigan MJ. Augmentation of protein degradation by L-triiodothy-
ronine in uremia. Metabolism 1989;38:1210–5.
 Becker RA, Vaughan GM, Ziegler MG, et al. Hypermetabolic low triiodothyronine
syndrome of burn injury. Crit Care Med 1982;10:870–5.
 Peeters RP, van der Geyten S, Wouters PJ, et al. Tissue thyroid hormone levels in critical
illness. J Clin Endocrinol Metab 2005;90:6498–507.
 Van den Berghe G, Baxter RC, Weekers F, et al. The combined administration of GH-
releasing peptide-2 (GHRP-2), TRH and GnRH to men with prolonged critical illness
evokes superior endocrine and metabolic effects compared to treatment with GHRP-2
alone. Clin Endocrinol (Oxf) 2002;56:655–69.
 Brent GA, Hershman JM. Thyroxine therapy in patients with severe nonthyroidal illnesses
and lower serum thyroxine concentration. J Clin Endocrinol Metab 1986;63:1–8.
ADLER & WARTOFSKY