Hyperthyroidism decreases body muscle mass and serum creatinine concentrations which can confound diagnosis of concurrent chronic kidney disease (CKD). Serum symmetric dimethylarginine (SDMA) concentrations are influenced to a lesser extent by muscle mass, and might be a better biomarker of CKD in hyperthyroidism. This study aimed to evaluate serum SDMA concentrations in hyperthyroid cats with and without azotemic CKD.
Hyperthyroid and euthyroid (without azotemic CKD [control]) cats >9 years old were included. Hyperthyroid cats received anti-thyroid medication and were monitored for azotemia (serum creatinine concentration >1.7 mg/dL) during a three month follow up period. Hyperthyroid cats that were azotemic before treatment or during follow up were included in the hyperthyroid-CKD group. Kruskal-Wallis with Dunn ‘s multiple comparisons test was used to compare baseline serum creatinine and SDMA concentrations (SDMA measured by IDEXX Laboratories) between the control, hyperthyroid-CKD and hyperthyroid non-azotemic groups. Median (range) values are presented.
Serum creatinine concentrations in control (1.4 [1.1–1.8] mg/dL, n=8) and hyperthyroid groups were not significantly different, however, serum creatinine was significantly higher in the hyperthyroid-CKD group (1.9 [1.1–2.4] mg/dL, n=5) than the hyperthyroid non-azotemic group (1.1 [0.7–1.3] mg/dL, n=4; p<0.05). Serum SDMA concentrations were not significantly (p>0.05) different between the control (11 [9–13] μg/dL), hyperthyroid-CKD (14 [7–17] μg/dL) and hyperthyroid non-azotemic groups (13 [11–19] μg/dL).
Serum SDMA concentrations did not distinguish hyperthyroid cats with and without azotemic CKD. The influence of hyperthyroidism on serum SDMA concentrations warrants further investigation.