Thyroid function testing in Greyhounds.

OBJECTIVE: To evaluate thyroid function in healthy Greyhounds, compared with healthy non-Greyhound pet dogs, and to establish appropriate reference range values for Greyhounds. ANIMALS: 98 clinically normal Greyhounds and 19 clinically normal non-Greyhounds. PROCEDURES: Greyhounds were in 2 groups as follows: those receiving testosterone for estrus suppression (T-group Greyhounds) and those not receiving estrus suppressive medication (NT-group Greyhounds). Serum thyroxine (T4) and free thyroxine (fT4) concentrations were determined before and after administration of thyroid-stimulating hormone (TSH) and thyroid-releasing hormone (TRH). Basal serum canine thyroid stimulating hormone (cTSH) concentrations were determined on available stored sera. RESULTS: Basal serum T4 and fT4 concentrations were significantly lower in Greyhounds than in non-Greyhounds. Serum T4 concentrations after TSH and TRH administration were significantly lower in Greyhounds than in non-Greyhounds. Serum fT4 concentrations after TSH and TRH administration were significantly lower in NT-group than T-group Greyhounds and non-Greyhounds. Mean cTSH concentrations were not different between Greyhounds and non-Greyhounds. CONCLUSIONS AND CLINICAL RELEVANCE: Previously established canine reference range values for basal serum T4 and fT4 may not be appropriate for use in Greyhounds. Greyhound-specific reference range values for basal serum T4 and fT4 concentrations should be applied when evaluating thyroid function in Greyhounds. Basal cTSH concentrations in Greyhounds are similar to non-Greyhound pet dogs.     

Thyroid testing in Sloughis

Background: Thyroid hormone concentrations were found to be different in Greyhounds and Whippets compared with nonsight hound dogs.
Hypothesis: In Sloughis, thyroid hormone concentration is lower than in nonsight hounds and comparable to Greyhounds.
Animals: Fifty-one Sloughis with no evidence of disease and a mean age of 4 years (range, 1–12 years).
Methods: Thyroid profiles consisting of total thyroxine (tT4), free thyroxine (fT4), free thyroxine after equilibrium dialysis (fT4 after ED), canine thyroid stimulation hormone (cTSH), and thyroglobulin antibodies as well as CBC and serum biochemistry results of Sloughis were compared with those of normal dogs. In 8 Sloughis, TSH stimulation tests were performed.
Results: In Sloughis, tT4 concentrations and fT4 concentrations measured by chemiluminescence were lower than those of controls (1.13 ± 0.65 μg/dL compared with 2.9 ± 0.8 μg/dL, P < .0001 and 11 ± 4.3 pmol/L compared with 16.7 ± 5.2 pmol/L, P < .0001, respectively). Concentrations of fT4 after ED and TSH were increased in Sloughis, when compared with controls (41.3 ± 26.9 pmol/L compared with 20.98 ± 10.29 pmol/L, P < .0001 and 0.22 ± 0.15 pmol/L compared with 0.15 ± 0.13 pmol/L, P = .0138, respectively). T4 concentration after TSH stimulation increased from 1.5 μg/dL (range, 0.2–2.7 μg/dL) to 2.7 μg/dL (range, 1.2–4.7 μg/dL); the recommended post-TSH T4 concentration was achieved by only 3 of 8 Sloughis. Hemoconcentration was found in 84.3% and hypoglobulinemia in 80.3%.
Conclusions and Clinical Importance: When evaluating Sloughis for hypothyroidism, veterinarians should be aware that these dogs have different thyroid hormone concentrations than nonsight hound dogs.     

Short-term influence of prednisone and phenobarbital on thyroid function in euthyroid dogs.

The short-term effects of prednisone and phenobarbital on serum total thyroxine (tT4), free thyroxine (fT4), and thyroid stimulating hormone (TSH) were evaluated in euthyroid dogs. Twenty-six beagles were randomly divided into 3 groups receiving, respectively, a placebo, prednisone (1.2 to 2 mg/kg body weight, per os, every 12 hours for 3 weeks), or phenobarbital (1.8 to 3 mg/kg body weight for 1 week, then 2.7 to 4.5 mg/kg body weight, per os, every 12 hours for 2 weeks). Blood samples taken over a 6-week period were assayed for serum tT4, fT4, and TSH. Phenobarbital therapy in our study did not affect serum tT4, fT4, or TSH concentrations. Prednisone therapy, however, significantly decreased serum tT4 and fT4, but did not affect serum TSH concentrations.     

Effects of oral administration of levothyroxine sodium on serum concentrations of thyroid gland hormones and responses to injections of thyrotropin-releasing hormone in healthy adult mares

OBJECTIVE: To determine the effects of levothyroxine sodium (L-T4) on serum concentrations of thyroid gland hormones and responses to injections of thyrotropin-releasing hormone (TRH) in euthyroid horses. ANIMALS: 12 healthy adult mares. PROCEDURE: 8 horses received an incrementally increasing dosage of L-T4 (24, 48, 72, or 96 mg of L-T4/d) for weeks 1 to 8. Each dose was provided for 2 weeks. Four additional horses remained untreated. Serum concentrations of total triiodothyronine (tT3), total thyroxine (tT4), free T3 (fT3), free T4 (fT4), and thyroid-stimulating hormone (TSH) were measured in samples obtained at weeks 0, 2, 4, 6, and 8; 1.2 mg of TRH was then administered i.v., and serum concentrations of thyroid gland hormones were measured 2 and 4 hours after injection. Serum reverseT3 (rT3) concentration was also measured in the samples collected at weeks 0 and 8. RESULTS: Treated horses lost a significant amount of weight (median, 19 kg). Significant treatment-by-time effects were detected for serum tT3, tT4, fT3, fT4, and TSH concentrations, and serum tT4 concentrations were positively correlated (r, 0.95) with time (and therefore dosage) in treated horses. Mean +/- SD serum rT3 concentration significantly increased in treated horses (3.06 +/- 0.51 nmol/L for week 8 vs 0.74 +/- 0.22 nmol/L for week 0). Serum tT3, tT4, fT3, and TSH concentrations in response to TRH injections differed significantly between treated and untreated horses. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of levothyroxine sodium increased serum tT4 concentrations and blunted responses toTRH injection in healthy euthyroid horses.     

Effect of dosing and sampling time on serum thyroxine, free thyroxine, and thyrotropin concentrations in dogs following multidose etodolac administration

Thirty-eight dogs with orthopedic disorders received etodolac, an NSAID, at 10.0 to 13.3 mg/kg PO once daily for 14 to 19 days. Mean total thyroxine (T4), free thyroxine (fT4), and canine thyrotropin (cTSH) values before and after etodolac administration were compared using paired t-tests. A significant (P <.05) decrease in T4 values occurred after etodolac administration with 21% of these values falling below the reference range. A significant (P <.05) increase in cTSH following etodolac administration, but none of the values was above the reference range. No significant changes occurred in mean fT4 values; however, 10% of the values fell below the reference range. In conclusion, T4 and fT4 test results should be interpreted with caution in dogs receiving etodolac.     

Evaluation of serum free thyroxine and thyrotropin concentrations in the diagnosis of canine hypothyroidism

Canine thyroid-stimulating hormone (cTSH), total thyroxine (T4) and free T4 by equilibrium dialysis (fT4d) were measured in serum samples from 107 dogs with clinical signs suggestive of hypothyroidism in which the diagnosis was either confirmed (n = 30) or excluded (n = 77) by exogenous TSH response testing. Median serum total T4 and fT4d concentrations were significantly lower and cTSH significantly higher (P < 0.001) in hypothyroid compared with euthyroid dogs. Differential positive rate analysis determined optimal cut-off values of less than 14.9 nmol/litre (total T4), less than 5.42 pmol/litre (fT4d), greater than 0.68 ng/ml (cTSH), less than 17.3 (T4 to cTSH ratio), and less than 7.5 (fT4d to cTSH ratio) for hypothyroidism. These had a sensitivity and specificity of 100 and 75.3 per cent, 80 and 93.5 per cent, 86.7 and 81.8 per cent, 86.7 and 92.2 per cent, and 80 and 97.4 per cent, respectively, for diagnosing hypothyroidism. Corresponding areas under the receiver operating characteristic curves were 0.92, 0.93, 0.87, 0.93 and 0.93. Unexpectedly low cTSH values in hypothyroid dogs may have resulted from concurrent non-thyroidal illness. Unexpectedly high serum cTSH values in the euthyroid dogs might have resulted from recovery from illness or concurrent potentiated sulphonamide therapy. Measurement of endogenous cTSH concentration is a valuable diagnostic tool for canine hypothyroidism if used in association with assessment of T4. Estimation of fT4d added only limited additional information over total T4 measurement.     

Effects of sulfamethoxazole-trimethoprim on thyroid function in dogs

OBJECTIVE: To evaluate effects of trimethoprim-sulfamethoxazole (T/SMX) on thyroid function in dogs. ANIMALS: 6 healthy euthyroid dogs. PROCEDURE: Dogs were administered T/SMX (14.1 to 16 mg/kg, PO, q 12 h) for 3 weeks. Blood was collected weekly for 6 weeks for determination of total thyroxine (TT4), free thyroxine (fT4), and canine thyroid-stimulating hormone (cTSH) concentrations. Schirmer tear tests were performed weekly. Blood was collected for CBC prior to antimicrobial treatment and at 3 and 6 weeks. RESULTS: 5 dogs had serum TT4 concentrations equal to or less than the lower reference limit, and 4 dogs had serum fT4 less than the lower reference limit after 3 weeks of T/SMX administration; cTSH concentrations were greater than the upper reference limit in 4 dogs. All dogs had TT4 and fT4 concentrations greater than the lower reference limit after T/SMX administration was discontinued for 1 week, and cTSH concentrations were less than reference range after T/SMX administration was discontinued for 2 weeks. Two dogs developed decreased tear production, which returned to normal after discontinuing administration. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that administration of T/SMX at a dosage of 14.1 to 16 mg/kg, PO, every 12 hours for 3 weeks caused decreased TT4 and fT4 concentrations and increased cTSH concentration, conditions that would be compatible with a diagnosis of hypothyroidism. Therefore, dogs should not have thyroid function evaluated while receiving this dosage of T/SMX for >2 weeks. These results are in contrast to those of a previous study of trimethoprim-sulfadiazine.     

Effects of deracoxib and aspirin on serum concentrations of thyroxine, 3,5,3'-triiodothyronine, free thyroxine, and thyroid-stimulating hormone in healthy dogs

OBJECTIVE: To evaluate the effects of deracoxib and aspirin on serum concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) in healthy dogs. ANIMALS: 24 dogs. PROCEDURE: Dogs were allocated to 1 of 3 groups of 8 dogs each. Dogs received the vehicle used for deracoxib tablets (PO, q 8 h; placebo), aspirin (23 to 25 mg/kg, PO, q 8 h), or deracoxib (1.25 to 1.8 mg/kg, PO, q 24 h) and placebo (PO, q 8 h) for 28 days. Measurement of serum concentrations of T4, T3, fT4, and TSH were performed 7 days before treatment (day -7), on days 14 and 28 of treatment, and 14 days after treatment was discontinued. Plasma total protein, albumin, and globulin concentrations were measured on days -7 and 28. RESULTS: Mean serum T4, fT4, and T3 concentrations decreased significantly from baseline on days 14 and 28 of treatment in dogs receiving aspirin, compared with those receiving placebo. Mean plasma total protein, albumin, and globulin concentrations on day 28 decreased significantly in dogs receiving aspirin, compared with those receiving placebo. Fourteen days after administration of aspirin was stopped, differences in hormone concentrations were no longer significant. Differences in serum TSH or the free fraction of T4 were not detected at any time. No significant difference in any of the analytes was detected at any time in dogs treated with deracoxib. CONCLUSIONS AND CLINICAL RELEVANCE: Aspirin had substantial suppressive effects on thyroid hormone concentrations in dogs. Treatment with high dosages of aspirin, but not deracoxib, should be discontinued prior to evaluation of thyroid function.     

Serum thyroid hormone concentrations and thyroglobulin autoantibodies in trained and non-trained healthy whippets

Numerous factors including non-thyroidal systemic diseases and drug administration can significantly alter canine thyroid function test results. Furthermore, the importance of breed specific variations has probably been underestimated. In this study, total thyroxine (TT4), free thyroxine (FT4), canine endogenous thyroid stimulating hormone (cTSH) serum concentrations and thyroglobulin autoantibodies (TgAA) were determined in a population of healthy whippets and compared to a control group of different breeds. Mean TT4 values were significantly lower in the whippets but no significant differences were seen between whippets and control dogs for FT4 and for cTSH. The prevalence of serum TgAA in the whippets was 2%, and this was not significantly different from the controls. The results suggest a breed variation for TT4, but not for FT4, cTSH and TgAA serum concentrations in whippets. Serum thyroid hormone concentrations were also compared between trained and non-trained whippets and it was concluded that regular training did not seem to have any significant influence.     

Comparison of colloid,thyroid follicular epithelium,and thyroid hormone concentrations in healthy and severely sick dogs

OBJECTIVES: To compare serum concentrations of total thyroxine (TT4), free thyroxine (fT4), and thyroid-stimulating hormone (TSH), as well as measures of thyroid follicular colloid and epithelium, between groups of healthy dogs and severely sick dogs. DESIGN: Cross-sectional study. ANIMALS: 61 healthy dogs and 66 severely sick dogs. PROCEDURE: Serum samples were obtained before euthanasia, and both thyroid lobes were removed immediately after euthanasia. Morphometric analyses were performed on each lobe, and serum TT4, fT4, and TSH concentrations were measured. RESULTS: In the sick group, serum TT4 and fT4 concentrations were less than reference range values in 39 (59%) and 21 (32%) dogs, respectively; only 5 (8%) dogs had high TSH concentrations. Mean serum TT4 and fT4 concentrations were significantly lower in the sick group, compared with the healthy group. In the healthy group, a significant negative correlation was found between volume percentage of colloid and TT4 or fT4 concentrations, and a significant positive correlation was found between volume percentage of follicular epithelium and TT4 or fT4 concentrations. A significant negative correlation was observed between volume percentages of colloid and follicular epithelium in both groups. CONCLUSIONS AND CLINICAL RELEVANCE: TT4 and fT4 concentrations are frequently less than reference range values in severely sick dogs. Therefore, thyroid status should not be evaluated during severe illness. The absence of any significant differences in mean volume percentages of follicular epithelium between healthy and severely sick dogs suggests that these 2 groups had similar potential for synthesizing and secreting thyroid hormones.     

Evaluation of recombinant human thyroid-stimulating hormone to test thyroid function in dogs suspected of having hypothyroidism

OBJECTIVE: To evaluate the use of recombinant human (rh) thyroid-stimulating hormone (TSH) in dogs with suspected hypothyroidism. ANIMALS: 64 dogs with clinical signs of hypothyroidism. PROCEDURES: Dogs received rhTSH (75 microg/dog, IV) at a dose independent of their body weight. Blood samples were taken before and 6 hours after rhTSH administration for determination of total serum thyroxine (T(4)) concentration. Dogs were placed into 1 of 3 groups as follows: those with normal (ie, poststimulation values indicative of euthyroidism), unchanged (ie, poststimulation values indicative of hypothyroidism; no thyroid gland stimulation), or intermediate (ie, poststimulation values between unchanged and normal values) post-TSH T(4) concentrations. Serum canine TSH (cTSH) concentration was determined in prestimulation serum (ie, before TSH administration). RESULTS: 14, 35, and 15 dogs had unchanged, normal, and intermediate post-TSH T(4) concentrations, respectively. Basal T(4) and post-TSH T(4) concentrations were significantly different among groups. On the basis of basal serum T(4) and cTSH concentrations alone, 1 euthyroid (normal post-TSH T(4), low basal T(4), and high cTSH concentrations) and 1 hypothyroid dog (unchanged post-TSH T(4) concentration and low to with-in reference range T(4) and cTSH concentrations) would have been misinterpreted as hypothyroid and euthyroid, respectively. Nine of the 15 dogs with intermediate post-TSHT(4) concentrations had received medication known to affect thyroid function prior to the test, and 2 of them had severe nonthyroidal disease. CONCLUSIONS AND CLINICAL RELEVANCE: The TSH-stimulation test with rhTSH is a valuable diagnostic tool to assess thyroid function in selected dogs in which a diagnosis of hypothyroidism cannot be based on basal T(4) and cTSH concentrations alone.     

Assessment of thyroid function in dogs with low plasma thyroxine concentration

BACKGROUND: Differentiation between hypothyroidism and nonthyroidal illness in dogs poses specific problems, because plasma total thyroxine (TT4) concentrations are often low in nonthyroidal illness, and plasma thyroid stimulating hormone (TSH) concentrations are frequently not high in primary hypothyroidism. HYPOTHESIS: The serum concentrations of the common basal biochemical variables (TT4, freeT4 [fT4], and TSH) overlap between dogs with hypothyroidism and dogs with nonthyroidal illness, but, with stimulation tests and quantitative measurement of thyroidal 99mTcO4(-) uptake, differentiation will be possible. ANIMALS: In 30 dogs with low plasma TT4 concentration, the final diagnosis was based upon histopathologic examination of thyroid tissue obtained by biopsy. Fourteen dogs had primary hypothyroidism, and 13 dogs had nonthyroidal illness. Two dogs had secondary hypothyroidism, and 1 dog had metastatic thyroid cancer. METHODS: The diagnostic value was assessed for (1) plasma concentrations of TT4, fT4, and TSH; (2) TSH-stimulation test; (3) plasma TSH concentration after stimulation with TSH-releasing hormone (TRH); (4) occurrence of thyroglobulin antibodies (TgAbs); and (5) thyroidal 99mTcO4(-) uptake. RESULTS: Plasma concentrations of TT4, fT4, TSH, and the hormone pairs TT4/TSH and fT4/TSH overlapped in the 2 groups, whereas, with TgAbs, there was 1 false-negative result. Results of the TSH- and TRH-stimulation tests did not meet earlier established diagnostic criteria, overlapped, or both. With a quantitative measurement of thyroidal 99mTcO4(-) uptake, there was no overlap between dogs with primary hypothyroidism and dogs with nonthyroidal illness. CONCLUSIONS AND CLINICAL IMPORTANCE: The results of this study confirm earlier observations that, in dogs, accurate biochemical diagnosis of primary hypothyroidism poses specific problems. Previous studies, in which the TSH-stimulation test was used as the "gold standard" for the diagnosis of hypothyroidism may have suffered from misclassification. Quantitative measurement of thyroidal 99mTcO- uptake has the highest discriminatory power with regard to the differentiation between primary hypothyroidism and nonthyroidal illness.     

Alterations in thyroid hormone concentrations in healthy sled dogs before and after athletic conditioning

OBJECTIVE: To determine effects of athletic conditioning on thyroid hormone concentrations in a population of healthy sled dogs. ANIMALS: 19 healthy adult sled dogs. PROCEDURE: Serum concentrations of thyroxine (T4), triiodothyronine (T3), thyroid-stimulating hormone (TSH), free T4 (fT4), free T3 (fT3), and autoantibodies directed against T3, T4, and thyroglobulin were measured in sled dogs that were not in training (ie, nonracing season) and again after dogs had been training at maximum athletic potential for 4 months. RESULTS: Analysis revealed significant decreases in T4 and fT4 concentrations and a significant increase in TSH concentration for dogs in the peak training state, compared with concentrations for dogs in the untrained state. Serum concentrations of T4 and fT4 were less than established reference ranges during the peak training state for 11 of 19 and 8 of 19 dogs, respectively; fT4 concentration was greater than the established reference range in 9 of 19 dogs in the untrained state. CONCLUSIONS AND CLINICAL RELEVANCE: Decreased total T4 and fT4 concentrations and increased serum concentrations of TSH were consistently measured during the peak training state in healthy sled dogs, compared with concentrations determined during the untrained state. Although thyroid hormone concentrations remained within the established reference ranges in many of the dogs, values that were outside the reference range in some dogs could potentially lead to an incorrect assessment of thyroid status. Endurance training has a profound impact on the thyroid hormone concentrations of competitive sled dogs.     

Assessment of serum thyroid hormone concentrations in lambs with selenium deficiency myopathy

OBJECTIVE: To assess changes in serum concentrations of thyroid hormones associated with selenium deficiency myopathy in lambs. ANIMALS: 35 lambs with selenium deficiency myopathy and 30 healthy lambs. PROCEDURES: Blood samples were collected via jugular venipuncture from lambs with selenium deficiency myopathy and healthy lambs. Activities of markers of selenium deficiency myopathy (erythrocyte glutathione peroxidase [GSH-Px] and plasma creatine kinase [CK]) and serum thyroid-stimulating hormone (TSH) and total thyroxine (tT(4)) and total triiodothyronine (tT(3)) concentrations were assessed; values in affected lambs were compared with those in healthy lambs. Correlations of erythrocyte GSH-Px and plasma CK activities with serum concentrations of TSH, tT(4), and tT(3) were investigated, and the tT(3):tT(4) concentration ratio was evaluated. RESULTS: Compared with findings in healthy lambs, erythrocyte GSH-Px activity, serum tT(3) concentration, and tT(3):tT(4) concentration ratio were significantly decreased and serum concentrations of tT(4) and TSH and the activity of plasma CK were significantly increased in affected lambs. Analysis revealed a significant negative correlation in the affected group between erythrocyte GSH-Px activity and each of the following: plasma CK activity (r = -0.443), serum TSH concentration (r = -0.599), serum tT(4) concentration (r = -0.577), and serum tT(3) concentration (r = -0.621). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that notable changes in circulating amounts of thyroid hormones develop in association with selenium deficiency in lambs. Such alterations in thyroid hormone metabolism may be involved in the high incidence of disorders, such as stillbirths and neonatal deaths, in selenium-deficient flocks.     

Results of thyroid function tests and concentrations of plasma proteins in dogs administered etodolac

OBJECTIVE: To determine the effects of etodolac administration on results of thyroid function tests and concentrations of plasma proteins in clinically normal dogs. Animals: 19 healthy random-source mixed-breed dogs. PROCEDURE: Blood samples for measurement of serum thyroxine (T4), 3,5,3'-triiodothyronine (T3), free T4 (fT4), and endogenous canine thyroid stimulating hormone (cTSH) were measured twice before as well as on days 14 and 28 of etodolac administration (mean dosage, 13.7 mg/kg, PO, q 24 h). Plasma total protein, albumin, and globulin concentrations and serum osmolality were measured once before as well as on days 14 and 28 of etodolac administration. RESULTS: Etodolac administration did not significantly affect serum T4, T3, fT4, or cTSH concentrations or serum osmolality. Significant decreases in plasma total protein, albumin, and globulin concentrations were detected on days 14 and 28 of administration. CONCLUSIONS AND CLINICAL RELEVANCE: Results of thyroid function tests are not altered when etodolac is administered for up to 4 weeks. Therefore, interpretation of results of these tests should accurately reflect thyroid function during etodolac treatment. Plasma total protein, albumin, or globulin concentrations that are less than the respective reference range in a dog administered etodolac for > or = 2 weeks may be an effect of treatment rather than an unrelated disease process. A decrease in plasma protein concentrations may reflect subclinical injury of the gastrointestinal tract.     

Effects of racing and nontraining on plasma thyroid hormone concentrations in sled dogs

OBJECTIVE: To determine the effects of racing and nontraining on plasma thyroxine (T4), free thyroxine (fT4), thyroid-stimulating hormone (TSH), and thyroglobulin autoantibody (TgAA) concentrations in sled dogs and compare results with reference ranges established for dogs of other breeds. DESIGN: Cross-sectional study. ANIMALS: 122 sled dogs. PROCEDURE: Plasma thyroid hormone concentrations were measured before dogs began and after they finished or were removed from the Iditarod Trail Sled Dog Race in Alaska and approximately 3 months after the race. RESULTS: Concentrations of T4 and fT4 before the race were less than the reference range for nonsled dogs in 26% and 18% of sled dogs, respectively. Immediately after racing, 92% of sled dogs had plasma T4 concentrations less than the reference range. Three months after the race, 25% of sled dogs had plasma T4 concentrations less than the reference range. For T4, fT4, TSH, and TgAA, significant differences were not detected in samples collected before the race versus 3 months later. CONCLUSIONS AND CLINICAL RELEVANCE: Plasma T4, fT4, and TSH concentrations decreased in dogs that complete a long distance sled dog race. Many clinically normal sled dogs have plasma T4 and fT4 values that are lower than the reference range for nonsled dogs. We suggest that the reference ranges for sled dogs are 5.3 to 40.3 nmol/L and 3.0 to 24.0 pmol/L for plasmaT4 and fT4 concentrations, respectively, and 8.0 to 370 mU/L for TSH.     

Comparison of thyroid analytes in dogs aggressive to familiar people and in non-aggressive dogs

A cross-sectional study was performed in order to examine the association between canine aggression to familiar people and serum concentrations of total thyroxine (TT4), free thyroxine (fT4), thyroxine autoantibodies (T4AA), total triiodothyronine (TT3), free triiodothyronine (fT3), triiodothyronine autoantibodies (T3AA), thyroid stimulating hormone (TSH), and thyroglobulin autoantibodies (TgAA). The subjects were 31 dogs historically aggressive to familiar people and 31 dogs with no history of aggression. Behavioral evaluation and physical examination were completed for each dog in addition to a complete blood count, serum chemistry panel, TT4, fT4 by equilibrium dialysis, TT3, fT3, TgAA, T3AA, and T4AA. Significant differences were found between the two groups with respect to only T4AA, which was increased in the aggressive group, but the concentrations for both groups were within the normal reference range. There were no differences between the two groups in the thyroid analytes most commonly measured by veterinary practitioners evaluating thyroid function in dogs. The results of this study revealed no significant difference between aggressive and non-aggressive dogs in the thyroid concentrations most commonly used to diagnose canine hypothyroidism.     

Effect of an anti-inflammatory dose of prednisone on thyroid hormone monitoring in hypothyroid dogs

It is not uncommon for a hypothyroid dog to be receiving concurrent corticosteroids. As hypothyroid dogs receiving thyroid supplement need periodic monitoring, knowledge of whether prednisone alters thyroid hormone concentrations would be useful to determine whether testing can or should be done while the dog is receiving therapy and whether dose adjustments are appropriate. In this study, the effect of short-term anti-inflammatory prednisone was determined in dogs with naturally occurring hypothyroidism. Eight adult dogs were given prednisone (1.0 mg/kg, orally) daily for 7 days and then on alternate days for 14 days. Serum total thyroxine (T(4) ), free T(4) (fT(4) ), and thyroid-stimulating hormone (TSH) were measured on days 7, 21 and 28 and compared with baseline data. Total T(4) concentrations were significantly decreased after 7 days of anti-inflammatory prednisone, but were not significantly altered from baseline on days 21 or 28. Free T(4) and TSH concentrations were not significantly altered from baseline at any point during the study. Two dogs had decreased total T(4) concentrations on day 7, which may have resulted in an alteration in thyroid supplementation. Results showed that administration of prednisone at a dosage of 1 mg/kg, orally, once daily for 7 days decreased total T(4) , while fT(4) was unchanged, suggesting that fT(4) may be less affected by daily prednisone administration. Anti-inflammatory doses of prednisone administered every other day did not interfere with thyroid hormone monitoring.     

Thyroid-stimulating hormone and total thyroxine concentrations in euthyroid, sick euthyroid and hypothyroid dogs

Canine thyroid-stimulating hormone (cTSH) was measured in a variety of clinical cases (n= 72). The cases were classified as euthyroid, sick euthyroid, hypothyroid or hypothyroid on non-thyroidal therapy on the basis of their history, clinical signs, laboratory results (including total thyroxine concentrations and, where indicated, thyroid-releasing hormone [TRH] stimulation tests) and response to appropriate therapy. Additional samples were taken during some of the TRH stimulation tests to measure the response of cTSH concentrations following TRH administration. A reference range (0 to 0–41 ng/ml) was calculated from the basal concentrations of cTSH in a group of 41 euthyroid dogs. Six of nine cases of confirmed hypothyroidism had basal cTSH concentrations above the reference range, whereas the remainder were within the normal range. One of these three remaining cases was a pituitary dwarf and did not show a rise in cTSH concentration following TRH stimulation. In contrast, only one of a group of six hypothyroid dogs that had been on non-thyroidal treatment within the previous four weeks had increased concentrations of basal cTSH. This study also found that five of a group of 16 dogs with sick euthyroid syndrome had increased cTSH concentrations. It was concluded that cTSH measurements are a useful additional diagnostic test in cases of suspected hypothyroidism in dogs but that dynamic testing is still required to confirm the diagnosis of hypothyroidism.     

Serum total thyroxine, total triiodothyronine, free thyroxine, and thyrotropin concentrations in epileptic dogs treated with anticonvulsants.

OBJECTIVE: To determine whether administration of phenobarbital, potassium bromide, or both drugs concurrently was associated with abnormalities in baseline serum total thyroxine (T4), triiodothyronine (T3), free T4, or thyrotropin (thyroid-stimulating hormone; TSH) concentrations in epileptic dogs. DESIGN: Prospective case series. ANIMALS: 78 dogs with seizure disorders that did not have any evidence of a thyroid disorder (55 treated with phenobarbital alone, 15 treated with phenobarbital and bromide, and 8 treated with bromide alone) and 150 clinically normal dogs that were not receiving any medication. PROCEDURE: Serum total T4, total T3, free T4, and TSH concentrations, as well as serum concentrations of anticonvulsant drugs, were measured in the 78 dogs with seizure disorders. Reference ranges for hormone concentrations were established on the basis of results from the 150 clinically normal dogs. RESULTS: Total and free T4 concentrations were significantly lower in dogs receiving phenobarbital (alone or with bromide), compared with concentrations in clinically normal dogs. Administration of bromide alone was not associated with low total or free T4 concentration. Total T3 and TSH concentrations did not differ among groups of dogs. CLINICAL IMPLICATIONS: Results indicate that serum total and free T4 concentrations may be low (i.e., in the range typical for dogs with hypothyroidism) in dogs treated with phenobarbital. Serum total T3 and TSH concentrations were not changed significantly in association with phenobarbital administration. Bromide treatment was not associated with any significant change in these serum thyroid hormone concentrations.