Reference change values of plasma and urine NGAL in cardiac surgery with cardiopulmonary bypass

As with any biomarker, interpretation of changes of NGAL concentration must consider its variability in a specific clinical setting. The aim of this study was to calculate the reference change value (RCV) and the index of individuality (II) of plasma and urine NGAL in the context of coronary artery bypass graft surgery with cardiopulmonary bypass, in patients without postoperative acute kidney injury.

This prospective single-center observational study included patients with a preoperative glomerular filtration rate of >30mlmin^-1 1.73m^-2, scheduled for elective coronary artery bypass graft with cardiopulmonary bypass and free from postoperative renal injury according to KDIGO criteria during hospital stay or a plasma creatinine Δ<0 (Δ=day1-induction). Plasma and urine NGAL were measured at anesthesia induction, 4h after intensive care admission and on the first and 2nd postoperative day and normalized to plasma proteins or urine creatinine. The RCV was given by the formula: 1.96×√2×√(CVa²+CVi²), were CVi is the intra-individual variability and CVa the reported analytical coefficient of variation of 5%. The II was calculated using the formula II=CVi/CVg for the four previous parameters, where CVg is the inter-individual variability.

Of the 100 patients enrolled in the study, 73 or 25 were considered free from acute kidney injury (KDIGO and Δ creatinine criteria, respectively) and included in the analysis. The RCV was 104% and 109% for plasma NGAL and 321% and 608% for urine NGAL. The II was <0.6 for both plasma and urine NGAL.

In patients who underwent coronary artery bypass grafting with normal post-operative kidney function, two-fold change in plasma NGAL and three to six-fold change in urine NGAL occur. In this specific clinical context, pathological variations must consider this biological "noise" for correct interpretation.