Effect of thyroxine supplementation on glomerular filtration rate in hypothyroid dogs

Abstract

Background: Glomerular filtration rate (GFR) is decreased in humans with hypothyroidism, but information about kidney function in dogs with hypothyroidism is lacking. Hypothesis: Hypothyroidism influences GFR in dogs. The objective of this study was to assess GFR in hypothyroid dogs before implementation of thyroxine supplementation and after re-establishing euthyroidism. Animals: Fourteen hypothyroid dogs without abnormalities on renal ultrasound examination or urinalysis. Methods: Blood pressure and GFR (measured by exogenous creatinine clearance) were measured before treatment (T0, n = 14) and at 1 month (T1, n = 14) and at 6 months (T6, n = 11) after beginning levothyroxine supplementation therapy (20 μg/kg/ d, PO). The response to therapy was monitored at T1 by measuring serum total thyroxine and thyroid stimulating hormone concentrations. If needed, levothyroxine dosage was adjusted and reassessed after 1 month. Statistical analysis was performed using a general linear model. Results are expressed as mean ± standard deviation. Results: At T0, the average age of dogs in the study group was 6.3 ± 1.4 years. Their average body weight decreased from 35 ± 18 kg at T0 to 27 ± 14 kg at T6 (P < .01).Conclusion: GFR was < 2 mL/min/kg in untreated hypothyroid dogs. Re-establishment of a euthyroid state increased GFR significantly. © 2009 by the American College of Veterinary Internal Medicine.