Retinol‐Binding Protein in Serum and Urine of Hyperthyroid Cats before and after Treatment with Radioiodine

Abstract

Retinol-binding protein (RBP) is suggested as a clinically useful marker of renal function in cats. Serum and urinary RBP concentrations in hyperthyroid (HT) cats differ from those in healthy (H) cats; radioiodine ((131)I) treatment influences serum and urinary RBP concentrations in HT cats. Ten HT and 8 H cats. RBP concentration was evaluated in feline serum and urine samples from a prospective study. There was a significant (P= .003) difference in the urinary RBP/creatinine (uRBP/c) ratios of H (-) and untreated HT (1.4 + or - 1.5 x 10(-2) microg/mg) cats. Serum total thyroxine concentration (1.8 + or - 1.9 microg/dL, 24 weeks) and uRBP/c (0.6 + or - 1.0 x 10(-2) microg/mg, 24 weeks) decreased significantly (P < .001) in HT cats at all time points after treatment with (131)I, and these variables were significantly correlated with one another (r= 0.42, P= .007). Serum RBP concentrations from HT cats (199 + or - 86 microg/L) did not differ significantly (P= .98) from those of H cats (174 + or - 60) and did not change after treatment with (131)I (182 + or - 124 microg/L, P= .80). The presence of urinary RBP in HT cats is a potential marker of tubular dysfunction that is correlated to thyroid status, although it is independent of circulating RBP concentrations. The decreased uRBP/c combined with the absence of changes in serum RBP after treatment suggests that the suspected tubular dysfunction was partly reversible with treatment of (131)I.