Urinary neutrophil gelatinase-associated lipocalin (uNGAL) as predictor of KDIGO-diagnosed cardiac surgery-associated acute kidney injury (CSA-AKI) and the composite outcome MAKE365.

Background and Goal of Study: 
uNGAL has been considered as a promising biomarker of CSA-AKI. However, its ability to predict CSA-AKI in the literature is inconsistent (AUC-ROC values ranging from 0.96 to 0.61).These discrepancies may be due to the wide range of CSA-AKI definitions. Current KDIGO classification combines the benefits of previous criteria, extending the diagnostic period to 7 days.
Moreover, it remains unclear how robust the relationship between uNGAL and renal outcomes actually is in clinical practice. Recently, a composite renal outcome measure of major adverse kidney events to 30 days (MAKE30) has been used in critically ill patients to capture an aggregate of renal outcomes of clinical importance.
Accordingly, we conducted a prospective observational study to investigate the relationship between uNGAL concentrations, KDIGO diagnosed CSA-AKI and MAKE at 365 days in cardiac surgical patients.

Materials and methods: 
We conducted a prospective observational study including all patients undergoing cardiac surgery during a nine-month period. Diagnosis of CSA-AKI was made using the KDIGO criteria. uNGAL was measured using the ARCHITECT platform at 4 time-points: baseline and postsurgery (admission ICU, day1 and day2). 
We defined MAKE365 as a composite outcome of death, use of renal replacement therapy, or persistence of renal dysfunction 1 year after surgery.
The ability of uNGAL to predict CSA-AKI and MAKE365 was assessed using the AUC-ROC.

Results and discussion: 
A cohort of 288 adult cardiac surgery patients. CSA-AKI occurred in 36.1% of patients. 53.8% developed stage 1; 24% developed CSA-AKI stage 2 and 22.2% developed stage 3. 22 of the 288 (7.6%) required RRT during ICU admission. No measure of uNGAL accurately predicted CSA-AKI (including severe stages) and MAKE365
Our findings suggest that the underlying relationship between CSA-AKI and uNGAL release is likely more complicated than is currently understood. Recent insights into the molecular nature of NGAL may offer a partial explanation. The limited ability of the NGAL assays to distinguish between the various molecular forms of uNGAL could be an explanation. NGAL might be a more specific AKI marker in settings where systemic inflammation is less pronounced.

Conclusion:
 uNGAL had a limited predictive ability for CSA-AKI and MAKE365. Adding uNGAL to the clinical early detection of CSA-AKI should wait until assays measuring kidney-specific NGAL are available.

Urinary neutrophil gelatinase-associated lipocalin (uNGAL) as predictor of KDIGO-diagnosed cardiac surgery-associated acute kidney injury (CSA-AKI) and the composite outcome MAKE365