NGAL in PD-related peritonitis: correlation with WBC over time and a possible role as outcome predictor.

Introduction The present study aimed to monitor pNGAL during peritonitis episodes, and to enhance its diagnostic value by evaluating pNGAL at scheduled times in parallel with White Blood Cells count. In addition, we investigated possible correlations between pNGAL and the etiology of peritonitis evaluating it as a possible marker of clinical outcome. Methods 22 patients with PD-related peritonitis were enrolled. Peritonitis was divided into Gram-positive, Gram-negative, polymicrobial, and sterile. WBC count and NGAL in peritoneal dialysis effluent (PDE) were measured at different times (day 0, 1st, 5th, 10th, 15th, and/or 20th, and 10 days after antibiotical therapy discontinuation). NGAL was measured by standard quantitative laboratory-based immunoassay and by colorimetric NGALds (dipstick test). Results We found strong correlations between peritoneal WBC, laboratory-based NGAL and NGALds values both overall and separated at each time point. On day 1, we observed no significant difference in WBC, both NGALds (p=0.3, 0.9, and 0.2) between Gram-positive, Gram-negative, polymicrobial and sterile peritonitis. No significant difference has been found between de novo versus relapsing peritonitis for all markers (p>0.05). We observed a parallel decrease of WBC and both NGAL in patients with favorable outcomes. WBC count and both peritoneal NGAL resulted higher in patients with negative outcomes (defined as relapsing peritonitis, peritonitis-associated catheter removal, peritonitis-associated HD transfer, peritonitis-associated death) at day 10 (p=0.04, p=0.03 and p=0.05; respectively) and day 15 (p=0.01, p=0.04 and tendency for p=0.005). There was a tendency towards higher levels of WBC and NGAL in patients with negative outcome at day 5. No significant difference in all parameters was proven at day 1 (p=0.3, p=0.9, p=0.2) between groups. Conclusion This study confirms peritoneal NGAL as a valid and reliable biomarker for the diagnosis of PD-peritonitis and its monitoring. Its trend is parallel to WBC count during peritonitis episodes, in particular, patients with unfavorable outcomes.