Serum free thyroxine concentration in healthy dogs, dogs with hypothyroidism, and euthyroid dogs with concurrent illness.
ABSTRACT Serum free thyroxine (fT4), thyroxine (T4), and 3,5,3'-triiodothyronine (T3) concentrations were determined in 62 healthy dogs, 51 dogs with hypothyroidism, and 59 euthyroid dogs with concurrent dermatopathy or concurrent illness for which hypothyroidism was a diagnostic consideration. Status of thyroid function was based on history, physical findings, results of thyrotropin response testing, requirement for thyroid hormone replacement therapy, and in 31 dogs, on results of histologic examination of a thyroid gland biopsy specimen. Serum fT4 concentration was determined, using a single-stage radioimmunoassay. Mean (+/- SD) serum fT4 concentration was significantly (P less than 0.05) greater in healthy dogs vs dogs with hypothyroidism (0.51 +/- 0.27 ng/dl vs 0.10 +/- 0.07 ng/dl). Significant difference in mean serum fT4 concentration was not evident between dogs with hypothyroidism and euthyroid dogs with hyperadrenocorticism (0.16 +/- 0.13 ng/dl) or peripheral neuropathy (0.19 +/- 0.10 ng/dl). Mean serum fT4 concentration in all other groups of euthyroid dogs with concurrent illness was similar to values in healthy dogs and was significantly (P less than 0.05) greater, compared with values in dogs with hypothyroidism. Similar results were found for mean serum T4 concentration. Comparison of serum fT4 vs T4 concentration revealed: sensitivity, 0.97 vs 0.98; specificity, 0.78 vs 0.73; predictive value for a positive test result, 0.79 vs 0.80; predictive value for a negative test result, 0.97 vs 0.97; and accuracy, 0.78 vs 0.86, respectively. Ten (17%) and 12 (20%) of 59 serum fT4 and T4 concentrations, respectively, were inappropriately low in euthyroid dogs with concurrent illness.(ABSTRACT TRUNCATED AT 250 WORDS)
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ABSTRACT: To assess use of serum thyroid hormone concentrations by veterinarians to diagnose hypothyroidism in sighthounds and to evaluate serum thyroid hormone concentrations in healthy Salukis. Retrospective case series and cross-sectional study. 398 sighthounds of various breeds with a diagnosis of hypothyroidism and 283 healthy Salukis. Pretreatment thyroid hormone assay results from sighthounds subsequently classified as hypothyroid by practitioners were retrieved from a laboratory database. In healthy Salukis, serum concentrations of total thyroxine (T(4)), free T(4), total triiodothyronine (T(3)), free T(3), and thyroid-stimulating hormone (TSH) and antibodies against thyroglobulin and thyroid hormones were assayed. Records indicated hypothyroidism had been diagnosed in 303 (76.1%) sight-hounds on the basis of low serum thyroid hormone concentrations alone and in 30 (7.5%) others despite all thyroid hormone indices being within reference limits. Only 65 (16.3%) dogs had a high TSH concentration or positive thyroglobulin autoantibody result to support the diagnosis. In healthy Salukis, median (reference limits) serum concentrations of total T(4), free T(4), total T(3), free T(3), and TSH were 13.0 nmol/L (2.8 to 40.0 nmol/L), 12.0 pmol/L (2.0 to 30.3 pmol/L), 1.0 nmol/L (0.4 to 2.1 nmol/L), 4.0 pmol/L (1.6 to 7.7 pmol/L), and 0.18 ng/mL (0 to 0.86 ng/mL), respectively. Diagnosis of hypothyroidism by practitioners was most often made without adequate supportive laboratory evidence. Thyroid hormone values in healthy Salukis differed markedly from standard reference limits for some, but not all, thyroid hormone indices. Breed-specific reference limits should be used when interpreting thyroid hormone profiles of sighthounds.Journal of the American Veterinary Medical Association 02/2010; 236(3):302-8. · 1.72 Impact Factor
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ABSTRACT: To assess thyroid hormone levels in hyperadrenocorticoid dogs before and after therapy with trilostane, a reversible inhibitor of steroidogenesis. Serum total thyroxine, free thyroxine and endogenous canine thyroid-stimulating hormone concentrations were measured in 20 dogs with spontaneously occurring hyperadrenocorticism before and six months after successful treatment with trilostane. Fourteen dogs demonstrated an increase in thyroxine following trilostane treatment; however, this was not significant (P=0.108). Fourteen dogs demonstrated an increase in canine thyroid-stimulating hormone concentrations with trilostane therapy (P=0.006). Of the 14 dogs that demonstrated an increase in thyroxine concentrations following therapy, 10 also showed an increase in canine thyroid-stimulating hormone concentrations. Before treatment, free thyroxine values were within, above and below the reference range in 10, six and two dogs, respectively. Sixteen of 18 dogs had free thyroxine values within the reference range after treatment, with 11 dogs showing a decrease in free thyroxine levels following therapy (P=0.029). While treatment with trilostane did not induce a significant change of thyroxine concentrations, there was a significant increase in canine thyroid-stimulating hormone concentrations following treatment, a finding that supports thyroid-stimulating hormone suppression as one of the factors that contributes to the effects of glucocorticoids on the hypothalamic-pituitary-thyroid axis. The significant elevation in free thyroxine values following treatment with trilostane was unexpected and did not support the findings of previous studies in this area.Journal of Small Animal Practice 04/2008; 49(3):139-43. · 1.18 Impact Factor
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ABSTRACT: This study was to determine the daily fluctuation of serum thyroxine (tT4), free thyroxine (fT4), 3,5,3'-triiodothyronine (T3) concentrations in healthy dogs. Thyroid function of these dogs was evaluated on the basis of results of TSH response test. Samples for the measurement of serum tT4, fT4, and T3 concentrations were obtained at 3- hour intervals from 8 : 00 to 20 : 00. Serum tT4, fT4, and T3 concentrations were measured by the enzyme chemiluminescent immunoassay (ECLIA). Mean T3 concentrations had no significant differences according to the sample collection time during the day. Mean tT4 and fT4 concentrations at 11 : 00 were 3.28 +/- 0.86 microg/dl and 1.30 +/- 0.37 ng/dl, respectively and mean tT4 and fT(4) at 14:00 were 3.54 +/- 1.15 microg/dl and 1.35 +/- 0.12 ng/dl, respectively. These concentrations were significantly high compared with tT4 and fT4 concentrations at 8:00, which were 1.75 +/- 0.75 microg/dl and 0.97 +/- 0.25 ng/dl, respectively (p < 0.05). According to the sample collection time, mean tT4 and fT4 concentrations changed with similar fluctuation during the day. Based on these results, it was considered that measurement of serum tT4 and fT4 concentrations from 11 : 00 to 14 : 00 might more easily diagnose the canine hypothyroidism in practice.Journal of Veterinary Science 03/2006; 7(1):25-9. · 0.93 Impact Factor