Changes in serum symmetric dimethylarginine concentrations after treatment of feline hyperthyroidism with antithyroid medications

ObjectivesThe aim of the present study was to report changes in serum creatinine and symmetric dimethylarginine (SDMA) concentrations after treatment of feline hyperthyroidism with anti thyroid medications and to compare these biomarkers at baseline between cats that were and were not azotaemic after treatment.MethodsIn this retrospective study, hyperthyroid cats that were euthyroid (total thyroxine [TT4] concentration 7-40 nmol/l) at 1 month (T1) and/or 2-9 months (T2) after treatment were identified and grouped by renal status defined by serum creatinine concentrations. Comparisons were made using non-parametric statistics and the correlations assessed using Spearman's correlation coefficient. Data are presented as median (minimum-maximum).ResultsA total of 19 hyperthyroid cats were included. At baseline, TT4 was negatively correlated with serum concentration of creatinine (<i>r</i>_s = -0.73; <i>P</i> <0.001) but not SDMA (<i>r</i>_s = -0.42; <i>P</i> = 0.074). Serum creatinine concentrations increased significantly at T1 and T2 (137 μmol/l [range 97-241] and 162 μmol/l [range 76-251]) compared with baseline (117 μmol/l [range 62-216]; <i>P</i> = 0.003 and <i>P</i> <0.001, respectively), whereas serum SDMA did not change significantly at T1 but did increase by T2 (11 μg/dl [range 8-29] and 13 μg/dl [range 9-24], respectively) compared with baseline (12 μg/dl [range 7-21]; <i>P</i> = 0.548 and <i>P</i> = 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 μg/dl [range 7-21], n = 13 vs 13 μg/dl [range 11-19], n = 6; <i>P</i> = 0.42).Conclusions and relevanceSerum SDMA concentrations are not helpful in predicting post-treatment azotaemia in initially non-azotaemic hyperthyroid cats treated with antithyroid medications and might be influenced by factors other than glomerular filtration rate in hyperthyroidism.