• Cats;
  • Thyroid;
  • Tubular function;
  • Urinary marker

Background: Retinol-binding protein (RBP) is suggested as a clinically useful marker of renal function in cats.

Hypothesis: Serum and urinary RBP concentrations in hyperthyroid (HT) cats differ from those in healthy (H) cats; radioiodine (131I) treatment influences serum and urinary RBP concentrations in HT cats.

Animals: Ten HT and 8 H cats.

Methods: RBP concentration was evaluated in feline serum and urine samples from a prospective study.

Results: There was a significant (P= .003) difference in the urinary RBP/creatinine (uRBP/c) ratios of H (−) and untreated HT (1.4 ± 1.5 × 10−2 μg/mg) cats. Serum total thyroxine concentration (1.8 ± 1.9 μg/dL, 24 weeks) and uRBP/c (0.6 ± 1.0 × 10−2 μg/mg, 24 weeks) decreased significantly (P < .001) in HT cats at all time points after treatment with 131I, and these variables were significantly correlated with one another (r= 0.42, P= .007). Serum RBP concentrations from HT cats (199 ± 86 μg/L) did not differ significantly (P= .98) from those of H cats (174 ± 60) and did not change after treatment with 131I (182 ± 124 μg/L, P= .80).

Conclusion and Clinical Importance: 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 131I.