Novel urinary biomarkers and the early detection of acute kidney injury after open cardiac surgeries

Background: Acute kidney injury (AKI) is a common complication after cardiac surgery, recently, several biomarkers have been used to facilitate early detection of AKI, including Neutrophil-gelatinase-associated-lipocalin (NGAL) and Kidney-injury-molecule-1 (KIM-1).This study was carried out to study the efficacy of urinary KIM-1 and NGAL separately and in combination in relation to early detection and assessment of severity of AKI after cardiac surgeries.

Methods: This prospective study was carried out on 45 adult patients, of both sexes, Cleveland score(CCS) (0-5) and scheduled for elective coronary artery bypass graft (CABG) surgery in Alexandria Main University Hospital, after approval of the ethical committee and having an informed written consent from every patient. Patients were screened for renal function tests before surgery and every day for 3 day after surgery. Freshly urine samples were taken from all patients and centrifuged for microscopic examination of the sediment: preoperative, 2, 12, 24, and 48 hr after cardiopulmonary bypass (CPB) and for measurement of NGAL and KIM-1; after induction, 2, 6, 12, and 24 hr after CPB. The primary end point was the incidence of AKI defined by the AKIN criteria of serum creatinine.

Results: 11 patients developed AKI. Patients with AKI had a higher AKIN stages and CCS. CPB time and cross clamp time were significantly higher in the AKI group with a mean of (90.5±16.2) and (60.9±8.1) minutes respectively. Serum creatinine started to be significantly higher in AKI group from the second postoperative day with a mean value of 1.56±0.28 mg/dl compared to a mean value of 0.85±0.14 mg/dl in non-AKI group. Urine sediment score(USS) 1 and 2 were higher in the AKI group than in the non-AKI group 2 hrs after CPB and till the end of the 2nd day with area under the curve (AUC) average of (0.865). Urinary NGAL significantly rise in AKI patients 2 and 6 hr after CPB with corresponding AUC of (0.710 and 0.700) but uKIM-1 was higher in the AKI group 12 and 24 hr after CPB with AUC (0.725 and 0.703) respectively. Combination of urinary NGAL, KIM-1, and USS yielded AUC of 0.906.

Conclusions: urinary NGAL is early sensitive but KIM-1which appears later than but is a more specific biomarker to ischemic renal injury. Urinary microscopic examination was found to be with very high sensitivity and specificity and injury site informative. The combination of more than one biomarker increases the accuracy of early detection of AKI after cardiac surgery.