Table 3.

Risk classification for severe AKI, based on clinical model and biomarkers

First Postoperative BiomarkerNRIIDI
Value (SE)PValue (SE)P
Urine IL-18 (pg/ml)0.22 (0.09)0.020.05 (0.02)0.006
Urine NGAL (ng/ml)0.17 (0.08)0.020.03 (0.01)0.04
Plasma NGAL (ng/ml)0.14 (0.06)0.020.05 (0.02)0.002
  • Severe AKI is defined as the receipt of dialysis or a doubling of serum creatinine during hospitalization. Clinical model is: age (per year), gender, white race, non-elective surgery, CPB time ≥120 minutes, RACHS ≥3, eGFR percentile, and site. NRI and IDI quantify the improvement of the biomarkers on predicting the risk of severe AKI. Comparing the clinical model to the clinical model with the biomarker, NRI considers it an improvement in reclassification if an AKI patient moves up a risk category or if a non-AKI patient moves to a lower risk category. Similarly a worse reclassification occurs if an AKI patient moves down a risk category or if a non-AKI patient moves up a risk category. Overall, NRI is the difference in the proportion of improvements in reclassification and the proportion of worse reclassifications. The IDI formula quantifies the reclassification continuously instead of categorically.