TSH Stimulation Test Research Articles

Retrospective Evaluation of Gastrointestinal Signs in Hypothyroid Dogs.

Few observations about gastrointestinal (GI) signs in hypothyroid dogs (hypo-T dogs) are available. We aimed to evaluate the prevalence and characteristics of concurrent GI signs in hypo-T dogs, describe clinicopathological, hepato-intestinal ultrasound findings in hypo-T dogs, investigate changes in GI signs after thyroid replacement therapy (THRT). Medical records of suspected hypo-T dogs from two hospitals were retrospectively reviewed. The inclusion criteria were: (1) having symptoms and clinicopathological abnormalities related to hypothyroidism (i.e., mild anemia, hyperlipemia); (2) not being affected by systemic acute disease; (3) not having received any treatment affecting thyroid axis. Hypothyroidism had to be confirmed using low fT4 or TT4 with high TSH and/or inadequate TSH-stimulation test response; otherwise, dogs were assigned to a euthyroid group. Clinical history, GI signs, hematobiochemical parameters, and abdominal ultrasound findings were recorded. Hypo-T dogs were assigned to the GI group (at least 2 GI signs) and not-GI group (1 or no GI signs). Follow-up information 3-5 weeks after THRT was recorded. In total, 110 medical records were screened: 31 dogs were hypo-T, and 79 were euthyroid. Hypo-T dogs showed a higher prevalence of GI signs (44%), especially constipation and diarrhea (p = 0.03 and p = 0.001), than euthyroid dogs (24%) (p = 0.04). Among hypo-T dogs, no difference in hematological parameters between GI and non-GI groups was found. Hypo-T dogs had a higher prevalence of gallbladder alterations than euthyroid dogs (20/25; 80% and 32/61; 52% p = 0.04). The hypo-T GI group showed a significant improvement in the GI signs after THRT (p < 0.0001). Specific investigation for concurrent GI diseases in hypo-T dogs was lacking; however, improvement in GI signs following THRT supports this association between GI signs and hypothyroidism.

Diagnostic utility of basal serum T4 and TSH concentrations in dogs with hypothyroidism confirmed by TSH stimulation test

Diagnostic utility of basal serum T4 and TSH concentrations in dogs with hypothyroidism confirmed by TSH stimulation test

Stroke vs. SIADH: A case of symptomatic hyponatremia secondary to SIADH in association with COVID-19 infection

A 66-year-old male with no known past medical history presented with history of two days of throbbing frontal headache associated with nausea, vomiting and left-sided facial droop. The patient also reported dizziness, subjective chills without cough, shortness of breath, or sputum production. Laboratory findings revealed elevated inflammatory markers but normal thyroid, kidney, and liver function tests. Initial sodium level was 126 mEq/L. Urine studies showed elevated urine osmolality of 647 mOsm/Kg and urine sodium level of 175 mEq/L, both suggestive of syndrome of inappropriate secretion of antidiuretic hormone (SIADH). The TSH and ACTH stimulation tests both came back as normal. CT scan of the chest showed no evidence of lung infiltrates. Diffusion weighted MRI of the brain showed no evidence of acute or subacute CVA. SARS-CoV-2 nasal swab test was resulted positive. With these findings we diagnosed our patient with SIADH. Patient was initially started on 3% saline infusion for symptomatic hyponatremia. A fluid restricted diet was enforced. Patient was also started on salt tablets in order to increase solute intake. Sodium slowly corrected throughout the hospitalization. Of note, our patient never became hypoxic, neither did he show evidence of clinical pneumonia. A CT imaging of the chest showed no lung infiltrates, and an MRI of the brain was negative for any acute intracranial abnormalities. This case highlights the role of early recognition of SIADH in the setting of SARS-CoV-2 infection even in the absence of hypoxemia or lung pathology.

Characterization of recombinant human and bovine thyroid-stimulating hormone preparations by mass spectrometry and determination of their endotoxin content

BackgroundThe TSH stimulation test to confirm canine hypothyroidism is commonly performed using a recombinant human TSH (rhTSH), as up to date, canine TSH is not yet commercially available. Limiting factors for the use of rhTSH are its high costs and occasional difficulties in product availability. Less expensive bovine TSH preparations (bTSH) purified from bovine pituitary glands are readily commercially available. The aim of this study was to evaluate two different bTSH products as alternative to rhTSH using mass spectrometry.ResultsMore than 50 proteins, including other pituitary hormones, bovine albumin, hemoglobin, and tissue proteins were identified in the bTSH preparations. In contrast, rhTSH proved to be a highly pure product. Significantly higher endotoxin levels could be detected in all bTSH products compared to the rhTSH.ConclusionsBoth bTSH products are crude mixtures and therefore not an acceptable alternative to rhTSH. Their use should be discouraged to prevent unintended side effects.

Die canine Hypothyreose – eine diagnostische Herausforderung?

Hypothyroidism is one of the most common endocrinopathies in dogs. Clinical symptoms and hematological and biochemical parameters lead to a first suspicion. To confirm diagnosis can be challenging, however. Determination of total serum T4 concentration is accepted as the primary screening test for the disease, and low serum T4 concentrations are intuitively suggestive of hypothyroidism. However it is well known that low T4 concentrations are frequently encountered in euthyroid dogs with various nonthyroidal diseases and in dogs receiving certain pharmacologic agents. Since assessment of endogenous TSH (canine TSH) using current canine TSH assays shows normal values in a high percentage of hypothyroid dogs (up to 40%), its diagnostic value is only limited. The TSH-stimulation test can still be recognized as the gold standard for the diagnosis of hypothyroidism in dogs. Determination of circulating T4 concentration before and 6 hours after the administration of exogenous TSH (recombinant human TSH, Thyrogen ® ) provides an assessment of the functional reserve capacity of the thyroid gland with minimal change in post-TSH T4 concentration, compared with the basal concentration, expected in dogs with hypothyroidism. Also this test can be influenced by nonthyroidal illness and by medications known to affect thyroid function. This suppressing influence seems to be less pronounced using a higher dose of TSH. Therefore, to improve the discriminatory power of the TSH stimulation test to differentiate between euthyroid-sick and primary hypothyroidism, the higher dose should be used in cases in which testing cannot be delayed. More recently, ultrasonography and scintigraphy have been used for the diagnosis of primary hypothyroidism. Using ultrasonography, a sensitivity of 98% was reported if size and echogenicity of the gland were combined. However, specificity was as low as 77% and care must be taken when measuring the gland because of a relatively high interobserver variability. Preliminary results using scintigraphy to discriminate between hypothyroid and non-thyroidal illness seem promising. However, due to its limited availability and the high expenditure, to date it cannot be used in clinical practice. Therefore, at present, if test results are obscure and a final diagnosis cannot be made, it is recommended to repeat the tests at a later time point.

Thyroid Testing in Sloughis

Thyroid hormone concentrations were found to be different in Greyhounds and Whippets compared with nonsight hound dogs. In Sloughis, thyroid hormone concentration is lower than in nonsight hounds and comparable to Greyhounds. Fifty-one Sloughis with no evidence of disease and a mean age of 4 years (range, 1-12 years). 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. In Sloughis, tT4 concentrations and fT4 concentrations measured by chemiluminescence were lower than those of controls (1.13+/-0.65 microg/dL compared with 2.9+/-0.8 microg/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 microg/dL (range, 0.2-2.7 microg/dL) to 2.7 microg/dL (range, 1.2-4.7 microg/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%. When evaluating Sloughis for hypothyroidism, veterinarians should be aware that these dogs have different thyroid hormone concentrations than nonsight hound dogs.

Assessment of Thyroid Function in Dogs with Low Plasma Thyroxine Concentration

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. 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. 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. 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. 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. 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.

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 thyroidal99mTcO4‐uptake, differentiation will be possible.Animals: In 30 dogs with low plasma TT4concentration, 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) thyroidal99mTcO4‐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 thyroidal99mTcO4‐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 thyroidal99mTcO‐uptake has the highest discriminatory power with regard to the differentiation between primary hypothyroidism and nonthyroidal illness.

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

To evaluate the use of recombinant human (rh) thyroid-stimulating hormone (TSH) in dogs with suspected hypothyroidism. 64 dogs with clinical signs of hypothyroidism. 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). 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. 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.

Evaluation of thyroid function in obese dogs and in dogs undergoing a weight loss protocol.

Obesity and weight loss have been shown to alter thyroid hormone homeostasis in humans. In dogs, obesity is the most common nutritional problem encountered and weight loss is the cornerstone of its treatment. Therefore, it is important to clarify how obesity and weight loss can affect thyroid function test results in that species. The objectives of this study were to compare thyroid function in obese dogs and in lean dogs and to explore the effects of caloric restriction and weight loss on thyroid hormone serum concentrations in obese dogs. In the first experiment, 12 healthy lean beagles and 12 obese beagles were compared. Thyroid function was evaluated by measuring serum concentrations of total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), thyrotropin (TSH), and reverse triiodothyronine (rT3) as well as a TSH stimulation test using 75 microg i.v. of recombinant human TSH. In the second experiment, eight obese beagles were fed an energy-restricted diet [average 63% maintenance energy requirement (MER)] until optimal weight was obtained. Blood samples for determination of TT4, FT4, TT3, TSH and rT3, were taken at the start and then weekly during weight loss. Only TT3 and TT4 serum concentrations were significantly higher in obese dogs as compared to lean dogs. In the second experiment, weight loss resulted in a significant decrease in TT3 and TSH serum concentrations. Thus obesity and energy restriction significantly alter thyroid homeostasis in dogs, but the observed changes are unlikely to affect interpretation of thyroid function test results in clinics.

Clinical, hematological, biochemical and endocrinological aspects of 32 dogs with hypothyroidism

During the years of 1996-2001, hypothyroidism was diagnosed at the clinic for small animal internal medicine, University of Zurich, in 32 dogs. Most of the dogs were large breeds. The most frequent clinical characteristics observed were exercise intolerance, obesity, dermatological, neurological and gastrointestinal signs. Predominant laboratory abnormalities were a low red blood cell count, increased concentration of cholesterol, triglycerides and fructosamin. 29 dogs had a T4 below the reference range (< 1.5 micrograms/dl), one dog had a T4 at the lower limit thereof (1.6 micrograms/dl). One dog had a T4 within the reference range (3.4 micrograms/dl), another had a very high T4 of 206.8 micrograms/dl; the results of the latter 2 dogs were interpreted as incorrectly increased T4 values due to in vitro interference with T4-autoantibodies. Diagnosis was confirmed in all of the dogs based on TSH-stimulation testing. Endogenous TSH (cTSH) measured parallelly, was elevated in only 60% of the dogs. In about 67% of the dogs, hypothyroidism was associated with thyroglobulin-autoantibodies. Canine hypothyroidism is a rather rare endocrine disorder in Switzerland. The TSH-stimulation test remains the gold standard in confirming the disease; a definitive diagnosis can be challenging for practitioners because bovine TSH, used for the TSH-stimulation test is not licensed for use in dogs. Since assessment of cTSH using current assays shows normal values in a high percentage of hypothyroid dogs, the diagnostic value is only limited. In most of the hypothyroid dogs T4 is decreased, with the presence of autoantibodies to T4, it can be normal or increased.

Measurement of serum total thyroxine, triiodothyronine, free thyroxine, and thyrotropin concentrations for diagnosis of hypothyroidism in dogs

Objective To determine whether measurement of baseline serum concentrations of total thyroxine (T4), triiodothyronine (T3), free T4, and thyrotropin (thyroid-stimulating hormone; TSH) would aid in the diagnosis of hypothyroidism in dogs. Design Prospective case series. Animals 54 dogs with hypothyroidism, 54 euthyroid dogs with nonthyroidal disease initially suspected to have hypothyroidism, and 150 clinically normal dogs. Procedure In the 54 dogs with hypothyroidism, diagnosis was established on the basis of clinical signs, results of routine laboratory and TSH stimulation tests, exclusion of concurrent nonthyroidal disease, and a good clinical response to treatment with l-thyroxine. Blood samples were collected from all dogs and were tested for thyroid hormone and TSH concentrations. Reference ranges for hormone concentrations were established on the basis of results for the 150 clinically normal dogs. Results Of the 54 hypothyroid dogs, 48 (89%) had low total T4 concentrations, 3 had low-normal concentrations, and 3 had high concentrations because of T4 autoantibodies. In contrast, only 10 (18%) euthyroid dogs had low total T4 concentrations. Only 3 of 31 (10%) hypothyroid dogs had low T3 concentrations; 23 had concentrations within the reference range, and 5 had high concentrations because of T3 autoantibodies. Only 3 of 38 euthyroid dogs had low T3 concentrations. Of the hypothyroid dogs, 53 (98%) had low free T4 concentrations and 1 had a low-normal concentration. Only 4 (7%) euthyroid dogs had low free T4 concentrations. Of the hypothyroid dogs, 41 (76%) had high TSH concentrations, and 13 had TSH concentrations within the reference range. Of the euthyroid dogs, only 4 (8%) had high TSH concentrations. Of all single hormone measurements evaluated, measurement of free T4 concentration had the highest sensitivity (0.98), specificity (0.93), and accuracy (0.95) as a test for hypothyroidism; measurement of total T4 concentration had a lower sensitivity (0.89), specificity (0.82), and accuracy (0.85). Compared with measurement of total or free T4 concentration, measurement of TSH concentration had a lower sensitivity (0.76) and accuracy (0.84) but specificity (0.93) equal to that for measurement of free T4 concentration. When T4 (total or free) and TSH concentrations were evaluated together, specificity was higher than when T4 or TSH concentration was evaluated alone. Only 1 euthyroid dog had low T4 (total and free) and high TSH concentrations. Clinical Implications Results indicate that measurement of serum free T4 and TSH concentrations is useful for diagnosis of hypothyroidism in dogs. About a quarter of the dogs with confirmed hypothyroidism, however, will have serum TSH concentrations within reference limits. (J Am Vet Med Assoc 1997;211:1396–1402)

Thyroid hormone plasmatic levels in rats treated with serotonin in acute and chronic way

Many experiments show that serotonin (5-HT) controls thyroidal function at hypothalamic level, inhibiting the TRH secretion. The majority of experiments are done in an acute way, consisting of a single serotonin dose injected intraperitoneally (ip) or intracerebroventricularly (ic) with the effect registered after a short time (usually 1 h) as in normal environmental conditions similar to the TSH stimulation test, that consists of transfer of the experimental animals from 30°C to 4°C for 30 min, thus inducing stimulation of the hypothalamus-hypophysis-thyroid axis. The aim of the present research was to study the correlation between 5-HT and the thyroidal function, measuring plasmatic thyroid hormone levels in rats ip treated in chronic (injected daily for 10 days with different doses of 5-HT), and in acute way (after 1 h from a single 2.0 mg/kg bw 5-HT dose) in normal environmental conditions to evidence the serotonin site action activity outside the blood-brain barrier. The results of the chronic experiment show an inhibitory effect of 5-HT, on T3 and T4 plasmatic level, only when it is injected at medium doses (0.2 and 0.4 mg/kg bw for T3, and 0.2 for T4), while the results of the acute experiment do not evidence any modification. These results show that in normal environmental conditions the outside 5-HT site action is active only when the 5-HT is injected chronically at defined doses, probably for a down-regulation phenomenon.

Thyroid Hormone Concentrations In Critically III Canine Intensive Care Patients

SummaryAlterations in thyroid indices in critically ill dogs were studied retrospectively to determine the incidence of the euthyroid sick syndrome and to assess its prognostic relevance to survival. Sixty‐seven dogs were classified as euthyroid bases on a TSH stimulation test. Forty‐one of 67 (61%) of the euthyroid dogs had low baseline serum T4concentrations (&lt;1.5 ug/dl) and 38 of 67 (56%) of the euthyroid dogs had low baseline serum T3concentrations (&lt;75 ng/dl). There was no significant difference between either the baseline or the post‐stimulation serum T4concentrations when values of dogs that survived were compared with those that died. There was, however, a significant difference (P&lt;0.05) between both the baseline and the post‐stimulation values for T3 when survivors (100.3± 81 ng/dl, 143± 66 ng/dl) and non‐survivors (64.2 ± 17.1 ng/dl, 96.6 ± 38.3 ng/dl) were compared. The euthyroid sick syndrome occurs commonly in critically ill dogs. Further, the extent of depression of serum concentrations of T3may be correlated to mortality.

Endocrine disease in pet birds

Disease affecting the avian endocrine system is discussed: neoplasia, goiter, hypothyroidism, hyperparathyroidism, hypocalcemia syndrome, adrenal conditions and diabetes mellitus. Clinical diagnostic procedures such as TSH and ACTH stimulation tests and the use of plasma insulin and glucagon concentrations are reviewed.

Update on Diagnosis of Canine Hypothyroidism

Until a clinically useful canine TSH assay is available, a valid test of thyroid hypofunction should (1) take into consideration valid (or at least predictive) measurement of the free T4 concentration in order to factor out the binding effects of drugs and nonthyroidal illness, and (2) should assess thyroid functional reserve. A validated equilibrium dialysis measurement of free T4 and the TSH stimulation test, provide the most useful diagnostic combination of tests now available. A therapeutic trial with L-thyroxine, despite being relatively safe, should be reserved once other diagnoses have been ruled out, and should be reevaluated to assure a clinical response which can be attributable to the medication.

Thyroid Scintigraphy During Antithyroid Treatment for Autonomous Nodules as a Means of Imaging Extranodular Tissue

The scintigraphic appearance of the thyroid gland after a course of methimazole treatment was studied in 22 patients with autonomous hot nodules. After 2-3 months of treatment the extranodular tissue was reactivated in almost every patient. This treatment constitutes an endogenous TSH stimulation test and may be used clinically in selected cases.

THE RADIOGRAPHIC APPEARANCE OF CANINE CONGENITAL HYPOTHYROIDISM: SKELETAL CHANGES WITH DELAYED TREATMENT

Congenital hypothyroidism was diagnosed in five Boxer dogs presented to the Veterinary Hospital of the University of Pennsylvania between 1978 and 1979. The dogs ranged in age from 5–19 months, and were from two unrelated litters. Congenital hypothyroidism was confirmed by serum T3 and T4 radioimmunoassay and TSH stimulation test. Serial radiographs made before and after L‐thyroxine oral supplementation were studied retrospectively to evaluate the resolution of skeletal abnormalities and to compare skeletal with chronological age. On initial presentation, all five dogs had the following skeletal manifestations of congenital hypothyroidism: short broad skulls, shortened vertebral bodies, and epiphyseal dysgenesis and delayed maturation. Epiphyseal dysgenesis was most common in the humeral (n = 3) and femoral condyles (n = 4), and proximal tibia (n = 4). Accelerated epiphyseal ossification occurred during thyroid hormone supplementation. Three dogs developed osteochondrosistype lesions. Bowing of the radius and disproportionate radius and ulna length resulted in humeroradial joint widening (n = 4) and humeroulnar joint subluxation (n = 1). Degenerative joint changes in the elbows (n = 4), stifles (n = 1), and shoulder (n = 1) were more common in the older dogs.

Use of Sensitive Immunoradiometric Assay for Thyrotropin in Clinical Practice

Although measurement of thyrotropin (thyroid-stimulating hormone; TSH) by radioimmunoassay was a major advance in the laboratory diagnosis of thyroid failure--replacing the time-consuming TSH stimulation test--it was not sufficiently sensitive to discriminate reliably between euthyroid and hyperthyroid patients. Measurement of the TSH response to thyrotropin releasing hormone (TRH) served this purpose, however. The recent development of TSH assays that are severalfold more sensitive and more specific than conventional radioimmunoassays has allowed distinction of euthyroid from hyperthyroid patients and eliminated the need for the TRH test. Although undetectable levels of TSH, compatible with hyperthyroidism, are occasionally noted in euthyroid patients with severe nonthyroidal illness and during the first trimester of pregnancy, false-positive results are less often recorded for TSH than for free or total thyroid hormone measurements. Measurement of TSH by sensitive immunoradiometric assay is currently the most useful first-line test of thyroid function in patients with suspected thyroid disease and, in addition, has a valuable role in monitoring the dose of thyroxine replacement therapy.

Clinical evaluation of thyroid function in racing pigeons (Columba livia domestica)

Reference values for basal thyroxine (T4) concentrations in racing pigeons are presented for use in clinical pathology. Values for basal plasma T4 concentrations in healthy racing pigeons over the four seasons were 6-35 nmol/litre. Significant differences were seen between seasons. To differentiate between primary hypothyroidism and other causes of lowered plasma T4 concentrations the optimum dose and sampling times for a TSH stimulation test in this species were determined. A convenient application of this test in the pigeon is to collect a blood sample at the end of a working day and then to administer 1 IU of TSH intramuscularly. The second blood sample is collected the following morning, about 16 hours later. In healthy pigeons T4 concentrations between 100 and 300 nmol/litre can be expected in the post-TSH sample representing a 3.5- to 15.3-fold increase above basal values.