Evaluation of Thyroid‐Stimulating Hormone, Total Thyroxine, and Free Thyroxine Concentrations in Hyperthyroid Cats Receiving Methimazole Treatment

Background Iatrogenic hypothyroidism (IH) after treatment of hyperthyroidism can impair renal function. No study compared the efficacy of measurement of serum free thyroxine by equilibrium dialysis (fT4ed) or thyroid‐stimulating hormone (TSH) concentrations for monitoring cats receiving methimazole....

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Bibliographic Details
Published in:Journal of veterinary internal medicine 2015-05, Vol.29 (3), p.862-868
Main Authors: Aldridge, C., Behrend, E.N., Martin, L.G., Refsal, K., Kemppainen, R.J., Lee, H.P., Chciuk, K.
Format: Article
Language:English
Subjects:
Animals
Antithyroid Agents - therapeutic use
Cat Diseases - blood
Cat Diseases - drug therapy
Cat Diseases - physiopathology
Cats
Creatinine
Equilibrium dialysis
Female
Hormones
Hyperthyroidism
Hyperthyroidism - blood
Hyperthyroidism - drug therapy
Hyperthyroidism - physiopathology
Hyperthyroidism - veterinary
Hypothyroidism
Independent study
Kidney diseases
Laboratories
Male
Methimazole - therapeutic use
Renal function
Subclinical
Thyroid
Thyroid gland
Thyroid-stimulating hormone
Thyrotropin - blood
Thyroxine
Thyroxine - blood
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Summary:Background Iatrogenic hypothyroidism (IH) after treatment of hyperthyroidism can impair renal function. No study compared the efficacy of measurement of serum free thyroxine by equilibrium dialysis (fT4ed) or thyroid‐stimulating hormone (TSH) concentrations for monitoring cats receiving methimazole. Objectives To (1) compare the ability of total T4 and fT4ed concentrations in conjunction with TSH to define thyroid function in hyperthyroid cats receiving methimazole, (2) determine the prevalence of IH in cats receiving methimazole, and (3) examine the relationship between thyroid axis hormones and serum creatinine concentration. Animals One hundred and twenty‐five serum samples from hyperthyroid cats receiving methimazole and total T4 concentrations ≤3.9 μg/dL. Methods Total T4, fT4ed, and TSH concentrations were measured to evaluate thyroid status and serum creatinine concentration was measured to assess renal function. A low total T4 or fT4ed concentration in combination with an increased TSH concentration defined IH. Results Forty‐one cats (33%) had increased TSH concentrations. Of cats with total T4 and fT4ed concentrations below the reference range, 68% and 73%, respectively, had TSH concentrations above the reference range. Only 18% of cats with a normal TSH concentration had an increased serum creatinine concentrations as compared to 39% of those with increased TSH concentrations (P 
ISSN:0891-6640
1939-1676
DOI:10.1111/jvim.12575