Reliable early prediction for different types of post-thyroidectomy hypocalcemia.

Abstract

High incidence of hypocalcemia after thyroidectomy is a major determinant in delay of discharge. Even though many studies have focused on the search for reliable early predictors of postoperative hypocalcemia, definitions of hypocalcemia are diverse; therefore, interpretation and application of previously reported findings may not be easy. We aimed to elucidate diverse patterns of post-thyroidectomy hypocalcemia and to provide reliable early predictors for these different types of hypocalcemia.
Retrospective chart review was performed and eligible 112 patients of thyroidectomy were categorized into four groups according to symptomatic and/or biochemical hypocalcemic criteria. A mismatch of occurrence and the timing of symptomatic or biochemical abnormalities were evaluated. Predictive values of commonly used biomarkers were compared in each group; levels of serum total calcium and ionized calcium, and intact parathyroid hormone (PTH).
Among 62 hypocalcemic patients, 45 patients (72.5%) experienced both symptomatic and biochemical abnormalities during hospitalization. A mismatch on the timing of initial detection of symptomatic and biochemical hypocalcemia was observed in 21 patients (46.6%). Intact PTH level measured at 1 hour was a useful indicator in prediction of symptomatic hypocalcemia with 79.7-87.4% of diagnostic accuracy. Serum ionized calcium measured next morning after surgery was a reliable predictor of biochemical hypocalcemia with 77.9-94.8% of diagnostic accuracy.
For the safety of patients, the possibility of both symptomatic and biochemical hypocalcemia should be considered together before deciding early discharge. Using intact PTH for symptomatic hypocalcemia and day-1 ionized serum calcium level for biochemical hypocalcemia will be helpful for the reliable prediction of heterogeneous nature of postoperative hypocalcemia.

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95
Copyright © 2011 by Korean Society of Otorhinolaryngology-Head and Neck Surgery.
This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0)
which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Reliable Early Prediction for Different Types of
Post-Thyroidectomy Hypocalcemia
Joon Ho Kim, MD*·Man Ki Chung, MD*·Young-Ik Son, MD
Department of Otorhinolaryngology-Head and Neck Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
DOI 10.3342/ceo.2011.4.2.95
Clinical and Experimental Otorhinolaryngology Vol. 4, No. 2: 95-100, June 2011
Original Article
INTRODUCTION
Hypocalcemia is one of the most common complications of thy-
roidectomy; the reported incidence of transient hypocalcemia
ranges from 0.3% to 49%, and that of permanent hypocalcemia
ranges from 0% to 13% (1). Given the high incidence of tran-
sient hypocalcemia, concerns about postoperative hypocalcemia
often become a major determinant in delay of early discharge
(2). Even though close monitoring of serum calcium level is a
standard of care for the patient who undergoes thyroidectomy
(3-6), it has limitations as an early predictor of postoperative hy-
pocalcemia, because the lowest concentration of serum calcium
is usually not reached until 48 hours after thyroidectomy (7).
Many recent studies have focused on the search for reliable
early predictors of postoperative hypocalcemia. Monitoring the
level of serum total calcium (Ca) or ionized calcium (iCa++), cal-
Objectives. High incidence of hypocalcemia after thyroidectomy is a major determinant in delay of discharge. Even though
many studies have focused on the search for reliable early predictors of postoperative hypocalcemia, definitions of
hypocalcemia are diverse; therefore, interpretation and application of previously reported findings may not be easy.
We aimed to elucidate diverse patterns of post-thyroidectomy hypocalcemia and to provide reliable early predictors
for these different types of hypocalcemia.
Methods. Retrospective chart review was performed and eligible 112 patients of thyroidectomy were categorized into four
groups according to symptomatic and/or biochemical hypocalcemic criteria. A mismatch of occurrence and the tim-
ing of symptomatic or biochemical abnormalities were evaluated. Predictive values of commonly used biomarkers
were compared in each group; levels of serum total calcium and ionized calcium, and intact parathyroid hormone
(PTH).
Results. Among 62 hypocalcemic patients, 45 patients (72.5%) experienced both symptomatic and biochemical abnormali-
ties during hospitalization. A mismatch on the timing of initial detection of symptomatic and biochemical hypocalce-
mia was observed in 21 patients (46.6%). Intact PTH level measured at 1 hour was a useful indicator in prediction of
symptomatic hypocalcemia with 79.7-87.4% of diagnostic accuracy. Serum ionized calcium measured next morning
after surgery was a reliable predictor of biochemical hypocalcemia with 77.9-94.8% of diagnostic accuracy.
Conclusion. For the safety of patients, the possibility of both symptomatic and biochemical hypocalcemia should be con-
sidered together before deciding early discharge. Using intact PTH for symptomatic hypocalcemia and day-1 ionized
serum calcium level for biochemical hypocalcemia will be helpful for the reliable prediction of heterogeneous nature
of postoperative hypocalcemia.
Key Words. Hypocalcemia, Parathyroid hormone, Thyroidectomy, Early diagnosis, Postoperative complicationns
• Received February 18, 2011
Accepted after revision April 13, 2011
• Corresponding author: Young-Ik Son, MD
Department of Otorhinolaryngology-Head and Neck Surgery, Samsung
Medical Center, Sungkyunkwan University School of Medicine,
50 Irwon-dong, Gangnam-gu, Seoul 135-710, Korea
Tel: +82-2-3410-3575, Fax: +82-2-3410-3879
E-mail: yison@skku.edu
*Both of them equally contributed to this study as the first author.

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96 Clinical and Experimental Otorhinolaryngology Vol. 4, No. 2: 95-100, June 2011
culating slopes in the change of Ca or iCa++ levels, measuring in-
traoperative or standard intact parathyroid hormone (iPTH) lev-
el, and making a new algorithm by combining more than two of
these values have all been reported as useful predictors (4, 8-11).
However, the definitions of hypocalcemia that were used in these
studies are diverse; therefore, the reported cut-off values of Ca,
iCa++, and PTH levels for prediction of hypocalcemia are also
widely variable. Moreover, some studies focused only on the
prediction of biochemical hypocalcemia (12, 13); however, in
practice, observation of a mismatch between the presence of hy-
pocalcemic symptoms and biochemical abnormalities is not un-
common. Therefore, there may be confusion in the interpreta-
tion of these data and limitations in the clinical application of
previously reported findings.
In this study, we subdivided the study cohort into four groups
according to symptomatic and/or biochemical hypocalcemic cri-
teria. Chronological dissociation in the initial presentation of hy-
pocalcemic symptoms and the initial detection of biochemical
hypocalcemia was evaluated in order to understand the differ-
ent characteristics of symptomatic and biochemical hypocalce-
mia. Predictive values of previously well-known biomarkers were
compared in each group; Ca and iCa++, iPTH, and the slopes of
changes in Ca, iCa++, and iPTH. A simple new algorithm is pro-
posed for the early and reliable prediction of post-thyroidecto-
my hypocalcemia; for both symptomatic and biochemical hypo-
calcemia.
MATERIALS AND METHODS
We retrospectively reviewed medical records of 123 consecutive
patients who underwent total thyroidectomy with or without
neck dissection (ND) and who were hospitalized for more than
3 days after the surgery between May 2004 and July 2005. At
that period of time, patients were usually hospitalized for more
than 3 days after surgery and daily routine follow-up of bioche-
mical markers were performed for screening of possible postop-
erative hypocalcemia. All the surgery was performed by one of
the authors (YIS). Operation records, progression notes, nursing
charts, and results of blood tests were noted. This study was ap-
proved by the Institutional Review Board of Samsung Medical
Center (IRB-2010-05-068-001).
Because Ca or iCa++ is known to reach its lowest level on the
third day after thyroidectomy in hypocalcemic patients (11), Ca
and iCa++ levels were measured before surgery (within 2 month
before surgery), at 1 hour, and every morning for 3 days after
surgery. Immediate postoperative level was checked at 1 hour
after surgery at PACU (post-anesthesia care unit). Using an im-
munoradiometric assay (ELSA-PTH, October 2004-model 13,
Cis bio international, France), blood iPTH (reference value of
our institution; 11-62 pg/mL) level was checked at 1 hour and
the next morning after surgery. Slopes of changes in Ca, iCa++,
and iPTH levels were calculated using values obtained at 1 hour
and the next morning after surgery (3). Routine biochemical tests
were repeated at 3 month after the surgery. If there was an evi-
dence of hypocalcemia, additional laboratory test was performed
according to the patients’ hypocalcemic status.
Among 123 patients, 11 patients were excluded from the study
due to missing one or more of the laboratory tests described abo-
ve. Twenty two male and 90 female patients (total 112 patients)
were finally enrolled for this study. Their ages ranged from 17 to
79 years old, with a mean of 51. One hundred seven patients
were diagnosed as papillary carcinoma, 4 patients as follicular
carcinoma, and 1 patient as medullary carcinoma. Total thyroid-
ectomy with ND (anterior compartment and/or lateral ND) was
performed in 70 patients (62.5%). Autotransplantation of para-
thyroid glands was performed in 29 patients (25.9%). Patients’
demographic characteristics are summarized at Table 1.
Table 1. Clinical characteristics of the patients
Variable S-B- group S+B+ groupS+B- group S-B+ groupP-value
No. of patients (%)
Sex (male:female)
Median age (years)
Histopathology of tumor
Papillary carcinoma
Follicular carcinoma
Medullary carcinoma
Size of tumor (cm)
Types of surgery
TT
TT with ACND
TT with ACND and LND
Parathyroid autotransplantation
Permanent hypocalcemia
50 (44.6)
10:40
50.1
45 (40.1)
8:37
48.0
9 (8.0)
2:7
47.0
8 (7.1)
2:6
57.5
0.979
0.123
48
2
-
42
2
1
9
-
-
8
-
-
0.770
1.95±2.2 1.8±2.42.5±2.31.4±0.830.822
29
15
6
7
0
7
24
14
15
4
1
4
4
0
2
2
4
3
0
0.001
0.236
0.1292 (1.8% )
S-B-: normocalcemia group; S+B+: symptomatic and biochemical hypocalcemia group; S+B-: only symptomatic hypocalcemia group; S-B+: only biochem-
ical hypocalcemia group; TT: total thyroidectomy; ACND: anterior compartment neck dissection; LND: lateral neck dissection.

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Kim JH et al.: Symptomatic and Biochemical Hypocalcemia after Thyroid Surgery 97
Symptomatic hypocalcemia was defined when there was any
episode of symptoms or signs of hypocalcemia during the hos-
pital stay; perioral numbness, tingling sense or paresthesia of
hands and/or feet, Chvostek sign, Trousseau sign, muscle cramp,
or tetany. The patients were asked to report any postoperative
symptoms and signs of hypocalcemia, which were educated by
corresponding medical staffs when they admitted to an inpatient
ward. If they reported their discomfort associated with hypocal-
cemia, an assigned nurse or a doctor determined whether it was
a real hypocalcemic symptom or non-specific one. When it was
regarded as a reliable hypocalcemic symptom, it was recorded
in the nursing chart or in the progression note and those events
were counted as symptomatic hypocalcemias in this study. Bio-
chemical hypocalcemia was defined when any one of the check-
ed Ca levels dropped below 8.0 mg/dL or when iCa++ level went
under 1.05 mmol/L. These values have been used to define post-
thyroidectomy hypocalcemia in much of the literature, although
they are lower than the reference ranges. In our hospital, refer-
ence value of Ca is in between 8.4 mg/dL and 10.2 mg/dL, and
that of iCa is in between 1.05 mmol/L and 1.35 mmol/L. Per-
manent hypocalcemia was defined as persistent symptomatic or
biochemical hypocalcemia for more than 6 months after the sur-
gery. Postoperatively, oral calcium supplements (calcium carbon-
ate 1.5 g per day) were routinely provided for all patients. Pa-
tients who developed symptomatic hypocalcemia were managed
with additional intravenous calcium gluconate and/or oral vita-
min D supplementation in addition to oral calcium carbonate.
For comparison of the characteristics of symptomatic vs. bio-
chemical hypocalcemia, patients were categorized into four gro-
ups; patients who presented with both symptomatic and bioche-
mical hypocalcemia (S+B+ group), patients with only symptom-
atic hypocalcemia (S+B- group), patients with only biochemical
hypocalcemia (S-B+ group), and patients without symptomatic
or biochemical evidence of hypocalcemia (S-B- group). Occur-
rence and onset timing of biochemical and symptomatic hypo-
calcemia are plotted in Fig. 1. Obtained values (mean±standard
deviations) of the candidate biomarkers, which included Ca,
iCa++, and iPTH levels at 1 hour or 1 day after surgery, and slopes
of the changes in Ca, iCa++, and iPTH levels are compared in Ta-
ble 2. Predictive accuracy of these biomarkers in each group are
summarized in Table 3.
Statistical analysis was performed using a commercially avail-
able software package (SPSS ver. 13.0; SPSS Inc., Chicago, IL,
USA). ANOVA test was used when comparing group means or
frequencies. Chi-square test was used for the analysis of diag-
nostic accuracy of different biomarkers between each group.
RESULTS
Incidence of hypocalcemia (Table 1)
Transient symptomatic or biochemical hypocalcemia developed
in 62 patients (62/112, 55.3%) and permanent hypocalcemia in
2 patients (1.8%). Among the 62 hypocalcemic patients, 45 pa-
tients (45/62, 72.5%) experienced both symptomatic and bio-
chemical abnormalities during the hospital stay; thus, they were
subgrouped into the S+B+ group. Nine patients (14.5%) met
the criteria for symptomatic hypocalcemia only (S+B- group),
while 8 patients (12.9%) showed only biochemical hypocalce-
mia (S-B+ group).
Anterior compartment ND was performed in 42 patients. Both
anterior compartment and lateral ND was performed in 28 pa-
tients (totally 70 patients). Lateral ND was performed as a ther-
apeutic intent in all patients. In contrast, clinical suspicion of an-
terior compartment lymph node metastasis was given in only
13 patients (31%). In overall, therapeutic ND was performed in
41 patients and prophylactic ND was performed in 29 patients.
In a prophylactic ND group (n=29), number of S-B- group was
10, S+B+ group was 13, S+B- group was 1, S-B+ group was 1
patient respectively. In a therapeutic ND group (n=41), S-B- gro-
up was 11, S+B+ group was 25, S+B- group was 4, S-B+ group
was 5 patients respectively. This was not a statistically significant
difference.
Fig. 1. Mismatch on the occurrence of symptomatic and biochemical
hypocalcemia. In 45 patients of the S+B+ group (triangles), 24 pa-
tients presented with symptomatic and biochemical abnormalities
on the same day (triangles along a dotted line) and the remaining
21 patients on different days of the hospital stay (scattered trian-
gles). Nine patients presented with only symptomatic hypocalcemia
(S+B- group, rectangles), while 8 patients revealed only biochemi-
cal hypocalcemia (S-B+ group, circles).
Biochemical & symptomatic hypocalcemia (S+B+ group)
Symtomatic hypocalcemia (S+B- group)
Biochemical hypocalcemia (S-B+ group)
Symptomati-
cally normal
Postoperative symptomatic hypocalcemia
Day 0Day 1Day 2Day 3
Day 3
Day 2
Day 1
Day 0
Postoperative biochemical hypocalcemia
Bio-
chemi-
cally
normal

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98 Clinical and Experimental Otorhinolaryngology Vol. 4, No. 2: 95-100, June 2011
Mismatch on the occurrence of symptomatic and biochemical
hypocalcemia (Fig. 1)
Of 45 patients in the S+B+ group, 24 patients (24/45, 53.3%)
presented with symptomatic and biochemical abnormalities on
the same day. A mismatch on the occurrence timing of symp-
tomatic or biochemical hypocalcemia was observed in the other
21 S+B+ patients (21/45, 46.6%), which corresponded to 33.9%
of all transient hypocalcemic patients (21/65). There was a 1-day
gap between the initial occurrence of symptoms/signs and bio-
chemical abnormality in 11 patients (17.7%), a 2-day gap in 8
patients (12.9%), and a 3-day gap in 2 patients (3.2%).
Comparison of biomarkers in each group (Table 2)
Mean values of Ca and iCa++ measured at 1 hour after surgery
in the recovery room were in the range of 8.31-8.68 mg/dL and
1.10-1.12 mmol/L, respectively, which were all above the hypo-
calcemic criteria in the every group. However, Ca and iCa++ mea-
sured on the morning after surgery (day 1) showed wide ranges
across the hypocalcemic criteria. Day 1 iCa++ level of S-B- pa-
tients (1.11±0.05 mmol/L) was within the reference value and
was statistically higher than that of S-B+ (1.01±0.05 mmol/L)
and S+B+ (0.99±0.07 mmol/L) patients, which belonged to the
criterion for biochemical hypocalcemia (1.05 mmol/L). Slopes
of changes in Ca or iCa++ levels were helpful in differentiation of
the S-B- group and S+B+ group, but not between the other gro-
ups. Standard iPTH levels of the S+B+ and S+B- groups mea-
sured either 1 hour or 1 day after surgery were all statistically
lower than those of the S-B- group and were below the reported
useful criterion, 10 pg/mL (14). However, those of the S-B+ group
were 13.8±9.87 pg/mL and 12.5±10.6 pg/mL, respectively,
which were not different from those of the S-B- group and above
the level of 10 pg/mL. None of the patients experienced symp-
Table 2. Comparison of measured parameters (mean±standard deviation) in each group
S-B- (n=50)S+B+ (n=45)S+B- (n=9)S-B+ (n=8)P-value
Total calcium (mg/dL)
Postop-1H
Next morning
8.68±0.42a
8.27±0.39b
8.31±0.58a
7.54±0.44b, c
8.72±0.67
8.00±0.39c
8.36±0.74
7.95±0.45
a <0.05
b <0.001
c <0.05
Ionized calcium (mmol/L)
Postop-1H
Day 1
1.12±0.04
1.11±0.05d, e
1.10±0.05
0.99±0.07d, f
1.11±0.05
1.06±0.04f
1.10±0.04
1.01±0.05e
NS
d, e <0.001
f <0.05
Slope of changes (postop-1H & day 1)
Total calcium
Ionized calcium
Standard iPTH (pg/mL)
Postop-1H
Day 1
-0.25±0.22g
-0.13±0.67h
-0.46±0.34g
-1.44±1.23h
-0.50±0.57
-0.65±0.60
-0.28±0.46
-1.17±0.36
g <0.05
h <0.001
20.7±12.7i, j
20.1±7.78k, l
4.04±2.82i
4.31±3.23k
5.62±3.55j
9.22±6.08l
13.8±9.87
12.5±10.6
i, j <0.001
k <0.001
l <0.05
S-B-: normocalcemic group; S+B+: symptomatic and biochemical hypocalcemic group; S+B-: symptomatic hypocalcemic group; S-B+: biochemical hy-
pocalcemic group; Postop-1H: levels measured at 1 hour after surgery; NS: not significant; a to l: each alphabet indicate that the certain P-value was cal-
culated from comparing the corresponding values that have been the same upper-note alphabet.
Table 3. Predictive abilities (%) of tested parameters in each hypo-
calcemic group
Sensitivity Specificity PPVNPVDA
Total calcium (mg/dL) at day 1
S+B+
S+B-
S-B+
Ionized calcium (mmol/L) at day 1
S+B+
S+B-
S-B+
Slope of changes between 1 hour and 1 day after surgery
Total calcium
S+B+88.9
S+B-77.8
S-B+87.5
Ionized calcium
S+B+93.3
S+B-88.9
S-B+100.0
Standard intact PTH (pg/mL)
One hour after surgery
S+B+100.0
S+B-100.0
S-B+50.0
Day 1
S+B+81.4
S+B-57.1
S-B+50.0
44.4
22.2
0.0
96.0
96.0
96.0
90.9
50.0
0.0
65.8
87.3
85.7
71.6
84.7
82.8
53.3
0.0
62.5
100.0
100.0
100.0
100.0
0.0
100.0
70.4
84.7
94.3
77.9
84.7
94.8
24.0
24.0
24.0
51.3
15.6
15.6
70.6
85.7
92.3
54.7
32.2
32.8
44.0
44.0
44.0
60.0
22.2
22.2
88.0
95.7
100.0
67.4
50.8
51.7
76.0
76.0
76.0
78.9
42.9
25.0
100.0
100.0
90.5
87.4
79.7
72.4
91.1
83.7
83.7
89.7
33.3
33.3
83.7
93.2
91.1
86.4
80.4
78.9
PPV: positive predictive value; NPV: negative predictive value; DA: diagno-
stic accuracy; S+B+: symptomatic and biochemical hypocalcemic group;
S+B-: symptomatic hypocalcemic group; S-B+: biochemical hypocalce-
mic group; PTH: parathyroid hormone.

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Kim JH et al.: Symptomatic and Biochemical Hypocalcemia after Thyroid Surgery 99
tomatic hypocalcemia when their postoperative iPTH level was
higher than 10 pg/mL.
Prediction of postoperative hypocalcemia (Table 3)
Overall diagnostic accuracy of day 1 Ca and iCa++ levels ranged
from 71.6% to 84.7% and 77.9% to 94.8%, respectively. Stan-
dard iPTH level measured 1 hour or 1 day after surgery exhibit-
ed diagnostic accuracies ranging between 72.4% and 87.4%.
However, slopes of changes in Ca or iCa++ levels showed much
poorer diagnostic accuracies ranging from 32.2% to 67.4%. In
the meanwhile, PTH level obtained at one hour after surgery
and iCa++ slope obtained at the next morning showed relatively
higher sensitivity than the other biomarkers.
DISCUSSION
This study demonstrated the heterogeneous nature of symptom-
atic and biochemical hypocalcemia. Among 62 hypocalcemic
patients, 17 patients (27.4%) exhibited either symptomatic or
biochemical hypocalcemia. Even though 45 of 62 hypocalcemic
patients (72.5%) experienced both symptomatic and biochemi-
cal abnormalities during their three-day hospital stay, 21 of these
patients (33.9%) had mismatches in the timing of initial presen-
tation or occurrence between symptomatic and biochemical hy-
pocalcemia. Therefore, for reliable prediction of postoperative
hypocalcemia, both symptomatic and biochemical hypocalce-
mic criteria should be considered together.
The reason for these mismatches in the timing of initial pre-
sentation or in the occurrence of symptomatic and biochemical
hypocalcemia is not clear. We speculate that routine postopera-
tive oral calcium supplementation might influence on develop-
ing symptomatic hypocalcemia and/or biochemical hypocalce-
mia. Routine supplementation of oral calcium might obscure an
early detection of hypocalcemia as well. Velocity of calcium re-
duction also influence on the onset of symptoms of hypocalce-
mia, since hypocalcemic symptoms are usually influenced not
only by serum total calcium level but also by the velocity of cal-
cium reduction (15). Another possibility is an over-diagnosis of
symptomatic hypocalcemia in this study since we defined as sym-
ptomatic hypocalcemia if there is any event of tingling sensation
regardless of its severity. In our study, numbness or tingling sense
of the lip, hands, or feet was the most common symptom. The
Chvostek sign was observed only in 5 patients. None of the pa-
tients experienced myalgia, muscle spasm, hypotension, or ab-
normal findings on EKG that were attributable to the low level
of serum calcium. In most of the cases, postoperative symptom-
atic hypocalcemia was easily controlled with intravenous infu-
sion of calcium gluconate±oral vitamin D administration.
Relatively strict criteria for hypocalcemia adopted in this study,
inclusion criteria of more than 3 days of hospitalization and se-
lection of the patient cohort who received total thryoidectomy±
ND, thus inducing a bias of selecting more patients with compli-
cations, might explain the relatively higher incidence of transient
hypocalcemia (58%) observed in this study. Also, designated stu-
dy period belongs to an early experience of thyroidectomy of
the author (YIS). And relatively higher rate of ND is also attrib-
uted to higher incidence of hypocalcemia. Anterior compartment
ND±lateral ND was performed in 70 of 112 patients (63%) and
hypocalcemia developed in 51 of these 70 patients (72.8%). Per-
manent hypocalcemia occurred in 2 patients (1.8%) of ND, and
these two patients belonged to the S+B+ group.
We performed autotransplantation of the parathyroid gland in
sternocleidomastoid muscle when discolored tissue was confir-
med as a parathyroid gland by frozen biopsy. One or two para-
thyroid glands was autotransplanted in 29 of 112 patients (25.9%),
and 22 of them (75.9%) experienced postoperative hypocalce-
mia. As noted before (16), higher incidence of hypocalcemia was
observed in this patient group of parathyroid autotransplantation
(Table 1, P=0.016).
Many studies have focused on the search for reliable early pre-
dictors of postoperative hypocalcemia in the hope of safe early
discharge after thyroidectomy, including continuous monitoring
of serum calcium level for at least postoperative 23 hours (16)
and routine oral calcium supplementation for all patients (17).
Even though an upward-sloping curve of Ca level is reported to
be predictive of no occurrence of postoperative hypocalcemia (3,
18), upward-sloping of Ca or iCa++ was an infrequent event (14%
or 21%, respectively) in this study and their diagnostic accura-
cies, specificities, and positive predictive values were relatively
poor. Because iPTH has a very short half life (less than 5 min-
utes) (19, 20) and a high sensitivity and high specificity ranging
between 80% to 100%, intraoperative iPTH is currently the most
emphasized biomarker (11, 12, 14, 21). In this study, iPTH level
measured at 1 hour after surgery showed high sensitivity and
high negative predictive value in the S+B+ and S+B- groups. And
none of the patients experienced symptomatic hypocalcemia
when postoperative iPTH level was higher than 10 pg/mL. How-
ever, its ability for prediction of the S-B+ group widely ranged
from 25.0% to 90.5%. Therefore, measurement of iPTH alone
will not be sufficient for safe and reliable prediction of heteroge-
neous types of postoperative hypocalcemia.
Given that 1) none of the patients was symptomatic when post-
operative iPTH level was higher than 10 pg/mL, 2) postopera-
tive iPTH level was a useful biomarker in differentiation of nor-
mocalcemic patients from S+B- or S+B+ patients with high di-
agnostic accuracies, and 3) day 1 iCa++ level was also useful in
differentiation of normocalcemia from hypocalcemia of S-B+ or
S+B+ patients with the highest diagnostic accuracy, we propose
a relatively simple guideline for an early and reliable prediction
of postoperative hypocalcemia by combining iPTH level and
day 1 iCa++ levels. When iPTH level measured about 1 hour af-
ter surgery is equal to or higher than 10 pg/mL, none of the pa-
tients will develop symptomatic hypocalcemia; therefore, early