Changes in serum symmetric dimethylarginine (SDMA) concentrations after treatment of feline hyperthyroidism with anti-thyroid medications

Objectives: To report changes in serum creatinine and symmetric dimethylarginine (SDMA) concentrations following treatment of feline hyperthyroidism with anti-thyroid medications and compare these biomarkers at baseline between cats that were and were not azotaemic after treatment. Methods: Retrospective study; hyperthyroid cats that were euthyroid (total thyroxine concentration (TT4) 7-40 nmol/L) at 1 month (T1) and/or 2-9 months (T2) following treatment were identified and grouped by renal status defined by serum creatinine concentrations post-treatment. Comparisons were made using non-parametric statistics, and the correlations assessed using Spearman’s correlation coefficient. Data are presented as median [minimum-maximum]. Results: Nineteen hyperthyroid cats were included. At baseline, TT4 was negatively correlated with serum concentrations of creatinine (rs = -0.73; P<0.001) but not SDMA (rs = -0.42; P=0.074). Serum creatinine concentrations increased significantly at T1 and T2 (137 [97-241] μmol/L and 162 [76-251] μmol/L) compared to baseline (117 [62-216] μmol/L; P=0.003 and P<0.001 respectively), whereas serum SDMA did not change significantly at T1 but did increase by T2 (11 [8-29] μg/dL and 13 [9-24] μg/dL respectively) compared to baseline (12 [7-21] μg/dL; P=0.548 and P=0.039 respectively). There was no significant difference in baseline serum SDMA between cats that were azotaemic after treatment and those that remained non-azotaemic (12 [7-21] μg/dL, n=13 vs. 13 [11-19] μg/dL, n=6; P=0.42). Conclusions and relevance: Serum SDMA concentrations are not helpful in predicting post-treatment azotaemia in initially non-azotaemic hyperthyroid cats treated with anti-thyroid medications, and might be influenced by factors other than glomerular filtration rate in hyperthyroidism.