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Objective

To determine circulating concentrations and fate of total and free thyroxine (T4) in cats with various illnesses not associated with the thyroid glands (non-thyroidal illnesses).

Design

Prospective study.

Animals

98 cats with nonthyroidal illness and 50 clinically normal cats.

Procedure

Serum total T4 concentrations were measured by radioimmunoassay, and serum free T4 concentrations were measured by direct equilibrium dialysis. Free T4 fraction was calculated from these 2 values.

Results

Serum total T4 concentrations were significantly (P < 0.001) lower in sick cats (mean ± SD, 17.18 ± 8.14 nmol/L), compared with healthy cats (mean ± SD, 26.00 ± 7.62 nmol/L). Serum total T4 concentrations were inversely correlated with mortality. Differences in serum free T4 concentrations in sick cats (mean ± SD, 27.70 ± 13.53 pmol/L), compared with healthy cats (mean ± SD, 24.79 ± 8.33 pmol/L), were not significant. A few sick cats had serum free T4 concentrations greater than the reference range. Calculated free T4 fraction was significantly (P < 0.001) greater in sick cats (mean ± SD, 0.24 ± 0.30%), compared with healthy cats (mean ± SD, 0.10 ± 0.06%).

Clinical Implications

Euthyroidism is maintained in sick cats, despite low serum total T4 concentrations. Measurement of serum total T4 concentrations is a valuable prognostic indicator. Serum free T4 concentrations should be used cautiously as a sole diagnostic criterion for confirmation of hyperthyroidism. (J Am Vet Med Assoc 1996;208:2004-2008)

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To document circulating total thyroxine (T4) and triiodothyronine (T3) responses after administration of thyrotropin (thyroid-stimulating hormone [TSH]) to hyperthyroid and healthy cats and assess the value of these responses as an additional diagnostic test for hyperthyroidism.

Design

Prospective case series.

Animals

21 healthy and 40 hyperthyroid cats.

Procedure

Serum total T4 and T3 concentrations were measured by radioimmunoassay before and 6 hours after administration of 0.5 IU of bovine TSH/kg of body weight.

Results

In healthy cats, serum total T4 concentration increased after administration of TSH (mean ± SD, 114.0 ± 36.4 nmol/L) representing a mean increment 3 times baseline concentration (mean ± SD, 33.7 ± 7.6 nmol/L). In hyperthyroid cats, the relative increase in serum total T4 concentration was significantly (P < 0.001) different; baseline values (mean ± SD, 236.2 ± 146.0 nmol/L) increased minimally after TSH administration (mean ± SD, 308.1 ± 178.9 nmol/L). There was a significant negative correlation (r s = −0.366) between relative increase in serum total T4 concentration after TSH administration and baseline concentration in hyperthyroid cats. In 3 cats with equivocal baseline serum total T4 concentration the T4 response to TSH administration was indistinguishable from that in healthy cats. Serum total T3 response to TSH administration was significantly (P < 0.001) lower in hyperthyroid, compared with healthy, cats but the T3 response in healthy cats was more variable than that for T4.

Conclusions

Thyrotoxic cats with high baseline serum total T4 concentration have a limited T4 response to TSH stimulation. Hyperthyroid cats with equivocal baseline serum total T4 concentrations have T4 responses after TSH stimulation similar to those of healthy cats. Measurement of serum total T3 concentration provides no additional information.

Clinical Relevance

The TSH response test is of limited value in diagnosing hyperthyroidism in cats. (Am J Vet Res 1996;57:987–991)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of Hct on blood glucose readings of dogs obtained by use of 2 point-of-care (POC) blood glucometers and a laboratory analyzer.

Animals—184 dogs, including 139 Greyhounds.

Procedures—Venous blood samples collected from 184 dogs with a range of Hcts (measured in EDTA-anticoagulated blood) were immediately analyzed with a handheld glucometer specifically developed for veterinary use and a glucometer developed for use in humans. The remainder of each blood sample was placed in fluoride oxalate tubes, and plasma glucose concentration was measured with a laboratory analyzer. Agreement between results for the POC glucometers and laboratory analyzer and effect of Hct on glucometer accuracy was assessed via regression analysis.

Results—Significant differences were detected between results of the glucometers and the reference laboratory analyzer. The Hct affected the correlation between results for the glucometers and the laboratory analyzer. Deviations of the glucometers from the reference interval varied with Hct. The glucometer for veterinary use more closely correlated with the glucose concentration when Hct was within or above its reference interval. The glucometer for use in humans more closely approximated laboratory reference glucose concentrations in anemic dogs.

Conclusions and Clinical Relevance—Hct had a relevant impact on the correlation between whole blood and plasma glucose concentrations in dogs. Significant variations between results obtained with the 2 glucometers could be critical when interpreting blood glucose measurements or selecting a POC glucometer for an intensive care setting and precise glycemic control in critically ill dogs.

Full access
in American Journal of Veterinary Research

Abstract

Objective—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.

Design—Retrospective case series and cross-sectional study.

Animals—398 sighthounds of various breeds with a diagnosis of hypothyroidism and 283 healthy Salukis.

Procedures—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 (T4), free T4, total triiodothyronine (T3), free T3, and thyroid-stimulating hormone (TSH) and antibodies against thyroglobulin and thyroid hormones were assayed.

Results—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 T4, free T4, total T3, free T3, 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.

Conclusions and Clinical Relevance—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.

Full access
in Journal of the American Veterinary Medical Association