Determination of Acute Kidney Injury by Neutrophil Gelatinase-Associated Lipocalin and Cystatin C Offers Precise and Prompt Identification of Patients at Risk of Prolonged Manifest Kidney Dysfunction after Heart Operations Using Cardiopulmonary Bypass

Objectives: To enhance recognition of potentially preventive therapy relevant AKI early after cardiac surgery, we already demonstrated superiority of neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C (CysC) over standard creatinine. The aim of the present study was to examine, whether NGAL nad CysC can identify patients with persistent AKI grade I or higher extending over 24 hours after surgery and/or with residual abnormally elevated Creatinine at discharge.

Methods: A total of 50 consecutive patients (mean age: 73 years, arterial hypertension: 86%, diabetes: 18%, EuroSCORE II: 2.20 and with eGFR > 60 mL/min/1.73 m²) undergoing cardiac surgery using CPB. Creatinine, NGAL and CysC were collected after induction of general anesthesia, further sampling occurred at CPB termination, 2 hours after CPB, on the first and second postoperative day. Patients were divided into AKI-group and Non-AKI-group and Persistent/Non-persistent AKI group, depending on the postoperative increase in serum creatinine and its duration (AKI I or higher extending over 24 hours for persistent Group).

Results: 35 patients (65%) did not develop persistent AKI and 15 patients did (35%).

Creatinine: Difference in persistent AKI versus nonpersistent AKI 2 hours after CPB and later on in 24h and 48h samples (87 ± 21 µmol/L vs. 75 ± 16 µmol/L, p = 0.044; 126 ± 39 µmol/L vs. 77 ± 22 µmol/L, p < 0.001; 139 ± 64 µmol/L vs. 67 ± 19 µmol/L, p < 0.001, respectively).

CysC: Difference in persistent AKI versus nonpersistent AKI already preoperatively, then 2 hours after CPB and in 24h and 48h post CPB samples (939 ± 218 µg/L vs. 764 ± 211 µg/L, p = 0.010; 929 ± 258 µg/L vs. 742 ± 251 µg/L, p = 0.021; 1465 ± 547 µg/L vs. 766 ± 185 µg/L, p < 0.001; 1567 ± 630 µg/L vs. 857 ± 287 µg/L, p = 0.001, respectively).

NGAL: Difference in persistent AKI versus nonpersistent AKI already at the end of CPB, then 2 hours after CPB, and in 24 and 48 hours post CPB samples (235 ± 81 µg/L vs. 186 ± 67 µg/L, p = 0.03; 204 ± 72 µg/L vs. 141 ± 60 µg/L, p = 0.002; 139 ± 51 µg/L vs. 70 ± 38 µg/L, p < 0.001; 133 ± 78 µg/L vs. 58 ± 31 µg/L, p = 0.002, respectively).

Conclusion NGAL and CysC better identify persistent AKI early after cardiac surgery than conventional Creatinine. As up to 35% AKI develops or worsens beyond 24 hours the application of these findings might enhance AKI diagnosis in the earliest postoperative window with potentially the broadest interventional possibilities leading to significant reduction of incidence and severity of post Cardiac Surgery Associated AKI.