Assessment of Renal Function in Hyperthyroid Cats Managed with Hill’s® Prescription Diet® Y/D® Feline

Vaske H., Armbrust L., Zicker S., et al. (2015).. ACVIM Forum. Indianapolis, Indiana: 568.


Previous studies demonstrated that glomerular filtration rate (GFR) declines with hyperthyroid treatment independent of the treatment modality. Hill’s® Prescription Diet® y/d® Feline is a controlled iodine food used to manage feline hyperthyroidism, however, its effects on renal function have not been evaluated. The purpose of this study was to assess the effects of y/d® Feline on renal function in hyperthyroid cats.

Hyperthyroidism was diagnosed in 15 client owned cats based on total thyroid hormone concentration (TT4) and compatible clinical signs. Baseline excretory renal function was assessed by plasma clearance of technetium diethylene-triamine-pentaacetate (GFR), serum creatinine (sCr), and serum symmetrical dimethyl arginine (SDMA) concentrations. Ultrasound was used to assess muscle mass (epaxial muscle diameter [EMD]). After an initial transition period to the food, it was then fed exclusively for 6 months and baseline parameters were re-assessed. A t-test was used to evaluate changes over time; a P-value <0.05 was considered significant.

Feeding y/d Feline for 6 months resulted in a significant decline in mean TT4 (185.5 vs. 60.5 nmol/l) and sCr (1.11 vs. 0.93 mg/dl). No change in GFR (2.31 vs. 2.26 ml/min/kg), SDMA (12.47 vs. 12.26 μg/dl), or EMD (left 1.56 vs. 1.62 cm and right 1.55 vs. 1.56 cm) was observed. SDMA better correlated with GFR than sCr (r2 0.50 vs. 0.30).

Although not all cats became/remained euthyroid during the study period, management with y/d® Feline reduced TT4 without decreasing GFR or EMD. Compared with sCr, SDMA may be a better marker of renal excretory function in hyperthyroid cats.