Efficacy of Urine Asymmetric Dimethylarginine Concentration to Predict Azotemia in Hyperthyroid Cats After Radio‐Iodine Treatment

Abstract

ABSTRACT Background Hyperthyroidism can mask concurrent chronic kidney disease in cats, and no accurate biomarkers are available to predict which cats will develop renal azotemia after radioiodine (131I) treatment. Hypothesis/Objectives To evaluate the potential of serum and urinary metabolites and metabolite ratios to predict post‐131I renal azotemia in hyperthyroid cats. Animals Hyperthyroid cats (n = 31), before and (3–12 months) after treatment with 131I at the Faculty of Veterinary Medicine (Ghent University, Belgium). Methods Retrospective study. Optimized and validated feline extraction and analysis protocols were employed for metabolic profiling of urine and serum samples using ultra‐high performance liquid chromatography–high‐resolution mass spectrometry. A dual strategy of cross‐validated univariate and penalized multivariate logistic regression was applied to determine predictivity (i.e., area under the curve [AUC], accuracy, sensitivity, and specificity) of individual biomarkers and panels. Results All hyperthyroid cats were non‐azotemic before 131I administration. After 131I treatment, 7 cats became persistently (≥ 2 timepoints) azotemic while 24 remained non‐azotemic. Urinary asymmetric dimethylarginine (ADMA) was identified as a pivotal predictor of post‐131I azotemia in both univariate and multivariate modeling. When employed as a standalone biomarker, an AUC of 0.851, accuracy of 0.903, sensitivity of 0.714, and specificity of 0.958 were achieved. While pre‐treatment USG was significantly different (P = 0.002) between both groups, it did not show enhanced prediction over ADMA, nor in multivariate modeling. Conclusions and Clinical Importance Urinary ADMA can accurately predict post‐131I azotemia in hyperthyroid cats becoming euthyroid after 131I treatment. These findings can aid clinicians in managing owner expectations and modify treatment plans.