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.

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.

BackgroundIn humans, measurement of serum thyroid‐stimulating hormone (TSH) concentration is commonly used as a first‐line discriminatory test of thyroid function. Recent reports indicate that canine TSH (cTSH) assays can be used to measure feline TSH and results can help diagnose or exclude hyperthyroidism.ObjectivesTo investigate the usefulness of cTSH measurements as a diagnostic test for cats with hyperthyroidism.AnimalsNine hundred and seventeen cats with untreated hyperthyroidism, 32 euthyroid cats suspected of having hyperthyroidism, and 131 clinically normal cats.MethodsProspective study. Cats referred to the Animal Endocrine Clinic for suspected hyperthyroidism were evaluated with serum T4, T3, free T4 (fT 4), and TSH concentrations. Thyroid scintigraphy was used as the gold standard to confirm or exclude hyperthyroidism.ResultsMedian serum TSH concentration in the hyperthyroid cats (<0.03 ng/mL) was significantly (P < .001) lower than concentrations in clinically normal cats (0.05 ng/mL) or euthyroid cats with suspected thyroid disease (0.06 ng/mL). Only 18 (2.0%) hyperthyroid cats had measurable TSH concentrations (≥0.03 ng/mL), whereas 114 (69.9%) of the 163 euthyroid cats had detectable concentrations. Combining serum TSH with T4 or fT 4 concentrations lowered the test sensitivity of TSH from 98.0 to 97.0%, but markedly increased overall test specificity (from 69.9 to 98.8%).Conclusions and Clinical ImportanceSerum TSH concentrations are suppressed in 98% of hyperthyroid cats, but concentrations are measurable in a few cats with mild‐to‐moderate hyperthyroidism. Measurement of serum TSH represents a highly sensitive but poorly specific test for diagnosis of hyperthyroidism and is best measured in combination with T4 and fT 4.

OBJECTIVES : The objectives of this study were to determine which serum thyroid hormone test best identifies iatrogenic hypothyroidism in cats that develop azotaemia after radioiodine treatment and to determine which thyroid test best differentiates these azotaemic, hypothyroid cats from azotaemic, radioiodine-treated euthyroid cats, as well as from azotaemic cats with chronic kidney disease and no history of thyroid disease. M ATERIALS AND M ETHODS : A total of 42 hyperthyroid cats that developed azotaemia (serum creatinine ê220 µmol/L) after radioiodine treatment had serum concentrations of thyroxine and free thyroxine by dialysis and thyroid -stimulating hormone measured at 3, 6 and 12 months. Iatrogenic hypothyroidism was confirmed (n=28) or excluded (n=14) on the basis of thyroid scintigraphy. A total of 14 cats with chronic kidney disease and 166 clinically normal cats underwent similar serum thyroid testing and scintigraphy.R ESULTS : Concentrations of thyroxine and free thyroxine were lower and thyroid-stimulating hormone higher in hypothyroid cats than in all three groups of euthyroid cats (P<0·0001). Of the hypothyroid cats, thyroxine and free thyroxine concentrations were low in 15 (53·6%) and seven (25%), respectively. Low serum thyroxine and free thyroxine concentrations were also detected in seven (50%) and two (14·3%) of the cats with chronic kidney disease. Thyroid-stimulating hormone concentrations were elevated in all hypothyroid cats but remained within the reference interval in all three groups of euthyroid cats.Serum thyroid -stimulating hormone had a higher test sensitivity and specificity than either thyroxine or free thyroxine concentration. C LINICAL SIGNIFICANCE : The finding of high serum thyroid-stimulating hormone concentrations best identifies feline iatrogenic hypothyroidism and differentiates it from non-thyroidal illness syndrome in cats that develop azotaemia after treatment. ttp://www.bsava.com/ M. E. Peterson et al.

The purpose of this study was t o evaluate fructosamine concentrations in clinically healthy cats, sick cats with stress hyperglycemia, and untreated diabetic cats t o determine the usefulness of this test in diagnosing diabetes mellitus in cats, and in differentiating the disease from stress-induced hyperglycemia. In addition, we evaluated if the degree of glycemic control in cats treated for diabetes influenced their serum fructosamine concentrations. In the 14 sick cats with stress hyperglycemia, the median serum fructosamine concentration (269 @mol/L) was not significantly different from the median value in the 26 clinically normal cats (252 pmol/ L). Two of the 14 cats with stress hyperglycemia (14.3%) had serum fructosamine concentrations above the upper limit of the reference range (175 t o 400 pmol/L); on the basis of these results, the test specificity was calculated as 0.86. In 30 cats with untreated diabetes mellitus, the median serum fructosamine concentration was 624 pmol/L, markedly higher than the value in either the normal cats or the cats with stress hyperglycemia. All but 2 of the 30 untreated n human diabetic patients, serum fructosamine concentra-I tion has been shown to provide a reliable assessment of short-term glucose homeostasis.'.' Fructosamine assays are reported to be quick, technically simple, inexpensive, precise, fairly free of interference, and easily a~t o m a t e d .~.~ The fructosamine test also detects deteriorating glycemic control faster than measurement of glycosylated hemoglobin, another test commonly used to monitor glycemic control in human diabetic patient^.'.^.'.^The term "fructosamine" refers to albumin and other plasma proteins that have been linked to a sugar (usually glucose) by a nonenzymatic chemical reaction, a process known as glycation. The serum fructosamine concentration is proportional to the blood glucose concentration over the life span of the glycated protein being measured (eg, in humans, 2 to 3 weeks in the case of albumin). Therefore, measuring the serum fructosamine concentration is a means of assessing the average blood glucose concentration in an individual over the preceding few weeks. Although the life span of albumin in cats is not known, it is assumed to be similar to that in dogs, approximately 1 to 2 weeks.' The glycation of hemoglobin over the life span of erythrocytes is commonly thought of as the classic example of this process and is a reflection of the average blood glucose concentration over the life span of the red blood cells (70 and 120 days in cats and humans, respectively).","