The aim of our study was to evaluate plasmatic and urinary NGAL and serum cystatin C as early
diagnostic markers of acute kidney injury in obese patients undergoing bariatric surgery.
For this this prospective observational study, we recruited 23 patients undergoing gastric by-pass or sleeve
gastrectomy, and admitted to the Low Dependence Unit after the surgery. Plasma NGAL (pNGAL), urinary NGAL
(uNGAL), serum cystatin C, serum creatinine, and serum urea were measured before surgery as well as 10 h and 24 h
Mean values of pNGAL, uNGAL, cystatin C, creatinine, and urea concentrations of pre- and post-surgery periods were
compared using Student’s t test for paired data. We also evaluated the presence of correlation between modifications of
NGAL and cystatin C after surgery and fluid balance, hydration (ml/kg) and diuresis using Pearson’s coefficient of
No patient developed AKI according to the AKIN criteria. pNGAL was significantly higher at T10th than T0(p=0.004). There was no significant difference between uNGAL at T0 and T10th (p=0.53) and between uNGAL at T0 and
T24th (p=0.31). uNGAL at T24th was significantly higher in comparison to T10th (p=0.024). uNGAL concentrations were
normal in all patients at every time step.
Cystatin C concentration did not increase after surgery.
Serum creatinine level was significantly higher at T48th, despite being still within the normal range, when compared to T0
Our study shows that pNGAL can reflect mild tubular damage as its levels increase within a few hours from
surgery and return to normal limits afterwards. Concerning uNGAL, there is a minimal increase at T24th, when NGAL
concentration in plasma has already decreased. Serum cystatin C does not show any relevant kidney changes, or at least,
no more than those ones shown by pNGAL.