Increased glomerular filtration rate (GFR) and decreased muscle mass make identification of chronic kidney disease (CKD) in hyperthyroid cats challenging. Symmetric dimethylarginine (SDMA) is a promising indirect renal biomarker that correlates closely with GFR in healthy geriatric and CKD cats. The aim of this study was to evaluate SDMA reliability as a renal biomarker in hyperthyroid cats. Forty-seven client-owned hyperthyroid non-azotemic (creatinine <168 μmol/l) cats were prospectively enrolled and treated with radioiodine (¹³¹I). Antithyroid medication was discontinued 10 days prior to ¹³¹I treatment. Cats had to be free of any other medication at least for 14 days prior to ¹³¹I treatment and free of any other clinically relevant systemic disease. Creatinine and SDMA (IDEXX SDMATM Test) were determined before (T0) and 1 month after (T1) treatment. GFR (plasma exogenous creatinine clearance test) was measured at T0 and T1 in 10 of 47 cats. As expected, creatinine significantly increased (p<0.001) and GFR significantly decreased (p<0.001) after ¹³¹I treatment. SDMA did not significantly change over time (p=0.37). Only 1 cat became azotemic (creatinine >168 μmol/l) at T1 while having normal SDMA at both time points. SDMA was elevated (>14 μg/dl) in 6 of 47 cats at T0 and normalised after treatment in 4 cats. GFR was available in 1 of these 6 cats and was within normal limits (SDMA normalised at T1). SDMA at T1 was increased above 14 μg/dl in 1 cat with borderline low GFR which was defined as GFR <1.9 ml/min/kg. Pearson correlation (n=10) between GFR and SDMA was moderate to low (r=-0.48, p=0.16 at T0 and r=-0.36, p=0.31 at T1) and correlation between GFR and creatinine was moderate (r=-0.54, p=0.11 at T0 and r=-0.51, p=0.13 at T1). Forty of forty-one cats with pre-treatment SDMA within reference interval remained non-azotemic post-treatment. However, not enough patients became azotemic post-treatment to evaluate if SDMA can predict post-treatment renal azotemia. Previous studies showed that SDMA is a promising renal biomarker but further studies are necessary to more fully assess its utility in feline hyperthyroidism.

Disclosures

Disclosures to report:

This study was supported by Idexx laboratories.