Introduction: Acute kidney injury (AKI) is a serious complication of cardiac surgery.
The current ‘gold standard’ for determining AKI is change in serum creatinine and urine output,
however, this change occurs relatively late after the actual injury occurs. Identification of new
biomarkers that detect early AKI is required. Recently, new biomarkers, such as the NephroCheck®
Test and AKIRisk have also been tested and found to be good indicators of AKI. Neutrophil
gelatinase-associated lipocalin (NGAL) has shown promise in paediatric patients but has displayed
varied results in adult populations, particularly post cardiac surgery. The aim of this study was to
assess the value of urinary NGAL as a biomarker of AKI in patients with pre-existing renal
impairment (eGFR >15ml/min to eGFR<60ml/min).
Methods: A post-hoc analysis of urinary NGAL concentrations from 125 patients with pre-existing
kidney impairment, who participated in a randomised trial of haemofiltration during cardiac
surgery, was undertaken. Urinary NGAL was measured using ELISA at baseline, post-operatively
and 24 and 48 hours after surgery, and serum creatinine was measured pre and postoperatively and
then at 24, 48, 72 and 96 hours as routine patient care. NGAL concentrations were compared in
patients with and without AKI determined by changes in serum creatinine concentrations. A
Kaplan-Meier plot compared survival for patients with or without AKI and a Cox proportional
hazards analysis was performed to identify factors with the greatest influence on survival.
Results: Following surgery, 43% of patients developed AKI (based on KDIGO definition). Baseline
urinary NGAL was not found to be significantly different between patients that did and did not
develop AKI. Urinary NGAL concentration was increased in all patients following surgery, regardless
of whether they developed AKI and was also significant between groups at 24 (p=0.003) and 48 hours
(p<0.0001). Urinary NGAL concentrations at 48 hours correlated with serum creatinine concentrations
at 48 hours (r=0.477, p<0.0001), 72 hours (r=0.488, p<0.0001) and 96 hours (r=0.463, p<0.0001).
Urinary NGAL at 48 hours after surgery strongly predicted AKI (AUC=0.76; P=0.0001). A Kaplan-
Meier plot showed that patients with postoperative AKI had a significantly lower 7-year survival
compared with those without AKI. Postoperative urinary NGAL at 48 hours >156ng/mL also strongly
predicted 7-year survival. However, additive EuroSCORE, age, current smoking and post-operative
antibiotics usage were distinctly significantly more predictive of 7-year survival as compared with
postoperative urinary NGAL at 48 hours >156ng/mL.
Conclusions: Our study demonstrated that postoperative urinary NGAL levels at 48 hours postsurgery
strongly predicts the onset or severity of postoperative AKI based on KDIGO classification
in patients with preoperative kidney impairment and were also strongly related to 7-year survival.