We introduce the use of a lanthanide complex, tetracycline–europium, for the clinical diagnosis of urea hydrogen peroxide in human
whole blood. The values obtained agree with the urea concentration variation verified in 49 patients, including 12 predialysis, 12 peritoneal, and 15 dialysis subjects, and 10 controls. This method is noninvasive and can help in the identification of renal and cardiac
diseases.