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

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.