Changes in symmetric dimethylarginine and glomerular filtration rates in hyperthyroid cats undergoing radioiodine therapy

Objectives The aims of this study were to evaluate concentrations of symmetric dimethylarginine (SDMA) in hyperthyroid cats before and after radioiodine treatment, and to compare results with other variables used to assess kidney function in cats (creatinine, urine specific gravity [USG] and glomerular filtration rate [GFR] measured by renal scintigraphy). Methods Thirteen cats diagnosed with hyperthyroidism based on clinical signs and increased serum total thyroxine (TT4) were included in this prospective study. Study design included physical examination, complete blood count, serum chemistry, TT4, urinalysis and SDMA before treatment (T0) and at 1 month (T1) and 3 months post-treatment (T3). GFR was quantified by renal scintigraphy at T0 and T3. Results Median GFR decreased significantly from baseline (3.18 ml/kg/min; range 1.35–4.87) at T3 (2.22 ml/kg/min; range 1.81–3.42 [P = 0.005]). While median creatinine and serum urea nitrogen increased post-treatment (creatinine: T0 = 0.8 mg/dl [range 0.4–1.1], T1 = 1.3 mg/dl [range 0.9–2]; T3 = 1.65 mg/dl [range 0.8–2.8]; P