Iron excretion in urine in patients with acute kidney injury after cardiac surgery

Hemolysis during cardiopulmonary bypass may lead to acute kidney injury caused by an excessive amount of iron. The clinical usefulness of the measurement of total iron concentration in the urine with the use of the atomic absorption spectrometry method for early identification of patients with postoperative acute kidney injury is not well-established. An observational, prospective study was conducted on a group of 88 pre-selected adult patients undergoing a planned coronary artery bypass grafting (CABG) procedure. The amount and concentrations of total iron, creatinine and neutrophil gelatinaseassociated lipocalin (NGAL) were evaluated in urine samples. A comparative analysis of the evaluated biochemical parameters was performed in regard to the occurrence of acute kidney injury 48 h postoperatively. Patients in the acute kidney injury group presented more advanced age (p = 0.01), preoperative myocardial infarction (p = 0.02), diuresis reduction (p = 0.04), and lower total iron levels in the 48-hour urine sample (p = 0.01). There was no difference when considering iron concentration in single urine samples in the study group. The sole result of total iron concentration in single urine samples is unreliable for the diagnosis of acute kidney injury after cardiac surgery. Decreased excretion of iron in the urine seems to be an important additional element in the multifactorial pathogenesis of acute postoperative kidney failure.