Search Results

You are looking at 1 - 5 of 5 items for

  • Author or Editor: Carlos Melián x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract

Objective—To determine the usefulness of measuring serum free thyroxine (T4) concentration as a diagnostic test for hyperthyroidism in cats, and to determine the influence of nonthyroidal disease on free T4 concentration in cats without hyperthyroidism.

Design—Prospective case series.

Animals—917 cats with untreated hyperthyroidism, 221 cats with nonthyroidal disease, and 172 clinically normal cats.

Procedure—Serum free T4, total T4, and total triiodothyronine (T3) concentrations were measured in cats with untreated hyperthyroidism and cats with nonthyroidal disease. Serum total T4 and T3 concentrations were determined by use of radioimmunoassay, and free T4 concentration was measured by use of direct equilibrium dialysis. Reference ranges for hormone concentrations were established on the basis of results from the 172 clinically normal cats.

Results—Sensitivity of serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly higher than the test sensitivity of either total T4 or T3 concentration. Of the 221 cats with nonthyroidal disease, 14 had a high free T4 concentration (ie, falsepositive result). Therefore, calculated specificity of measuring serum free T4 concentration as a diagnostic test for hyperthyroidism was significantly lower than test specificity of measuring either the total T4 or T3 concentration.

Conclusions and Clinical Relevance—Results indicate that determination of free T4 concentration is useful in the diagnosis of hyperthyroidism, especially in cats in which hyperthyroidism is suspected but total T4 and T3 concentrations are within reference ranges. However, because some cats with nonthyroidal disease have high serum free T4 concentrations, hyperthyroidism should not be diagnosed solely on the finding of high free T4 concentration. (J Am Vet Med Assoc 2001;218:529–536)

Full access
in Journal of the American Veterinary Medical Association

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)

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine whether nonthyroidal disease of various causes and severity is associated with abnormalities in baseline serum concentrations of total thyroxine (T4), triiodothyronine (T3), free T4, or thyrotropin (thyroid-stimulating hormone [TSH]) in dogs believed to be euthyroid.

Design—Case-control study.

Animals—223 dogs with confirmed nonthyroidal diseases and presumptive normal thyroid function, and 150 clinically normal dogs.

Procedure—Serum total T4, total T3, free T4, and TSH concentrations were measured in dogs with confirmed nonthyroidal disease. Reference ranges for hormone concentrations were established on the basis of results from 150 clinically normal dogs.

Results—In dogs with nonthyroidal disease, median serum concentrations of total T4, total T3, and free T4 were significantly lower than those in clinically normal dogs. Median serum TSH concentration in sick dogs was significantly greater than that of clinically normal dogs. When stratified by severity of disease (ie, mild, moderate, and severe), dogs with severe disease had low serum concentrations of total T4, total T3, or free T4 more commonly than did dogs with mild disease. In contrast, serum TSH concentrations were more likely to remain within the reference range regardless of severity of disease.

Conclusions and Clinical Relevance—Results indicate that serum total T4, free T4, and total T3 concentrations may be low (ie, in the hypothyroid range) in dogs with moderate to severe nonthyroidal disease. Serum TSH concentrations are more likely to remain within the reference range in sick dogs. (J Am Vet Med Assoc 2001;219:765–769)

Full access
in Journal of the American Veterinary Medical Association

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 (ie, 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. (J Am Vet Med Assoc 1999;214:1804-1808)

Free access
in Journal of the American Veterinary Medical Association

Objective

To determine whether low doses of synthetic ACTH could induce a maximal cortisol response in clinically normal dogs and to compare a low-dose ACTH stimulation protocol to a standard high-dose ACTH stimulation protocol in dogs with hyperadreno-corticism.

Design

Cohort study.

Animats

6 clinically normal dogs and 7 dogs with hyperadrenocorticism.

Procedure

Each clinically normal dog was given 1 of 3 doses of cosyntropin (1, 5, or 10 μg/kg [0.45, 2.3, or 4.5 μg/lb] of body weight, IV) in random order at 2-week intervals. Samples for determination of plasma cortisol and ACTH concentrations were obtained before and 30, 60, 90, and 120 minutes after ACTH administration. Each dog with hyperadrenocorticism was given 2 doses of cosyntropin (5 μg/kg or 250 μg/dog) in random order at 2-week intervals. In these dogs, samples for determination of plasma cortisol concentrations were obtained before and 60 minutes after ACTH administration.

Results

In the clinically normal dogs, peak cortisol concentration and area under the plasma cortisol response curve did not differ significantly among the 3 doses. However, mean plasma cortisol concentration in dogs given 1 μg/kg peaked at 60 minutes, whereas dogs given doses of 5 or 10 μg/kg had peak cortisol values at 90 minutes. In dogs with hyperadrenocorticism, significant differences were not detected between cortisol concentrations after administration of the low or high dose of cosyntropin.

Ctinical Implications

Administration of cosyntropin at a rate of 5 μg/kg resulted in maximal stimulation of the adrenal cortex in clinically normal dogs and dogs with hyperadrenocorticism. (J Am Vet Med Assoc 1999;214:1497-1501)

Free access
in Journal of the American Veterinary Medical Association