#758 NGAL dipstick for peritonitis: bridging the gap between rapid assessment and clinical efficiency in peritoneal dialysis
Authors: Morisi Niccolò , Virzì Grazia Maria , Manani Sabrina Milan , Alfano Gaetano , Castiglione Claudia , de Cal Massimo , Tantillo Ilaria , Donati Gabriele , Ronco Claudio , Zanella Monica 
Published: May 2024

Abstract

Background and Aims
Neutrophil gelatinase-associated lipocalin (NGAL) is a versatile protein known for its multifunctional roles, extending beyond its conventional use as a biomarker. It actively participates in crucial biological processes such as inflammation, proliferation, and migration. This study seeks to evaluate NGALds, a recently developed dipstick test, in comparison to the established laboratory method (NGALlab) for the early detection of peritonitis related to peritoneal dialysis (PD). The focus of the investigation lies in analyzing peritoneal fluid to develop a rapid and effective diagnostic tool, aiming to enhance the management of peritonitis.

Method
A retrospective analysis was undertaken to validate diagnostic accuracy, utilizing parallel samples obtained from peritoneal effluents. Samples were obtained from both PD stable patients undergoing routine analysis and from PD patients with suspected or confirmed peritonitis. The assessment of NGALds involved a direct comparison with the established NGALlab. Peritoneal NGALlab quantification was conducted using the BioPorto test, employing a particle-enhanced turbidimetric immunoassay. The NGALds, a rapid semi-quantitative assay, utilized colorimetric test strips and an antibody sandwich lateral flow dipstick test. The greatest value of NGAL detected by dipstick is 600 μg/L. Statistical analyses, including Spearman rank correlation coefficients (Rs), were performed with SPSS Statistics 26.0 software. Additionally, ROC analysis was carried out using white cell count and percentage of Neutrophils in peritoneal fluids as the gold standard.

Results
Among the 301 peritoneal effluent samples analyzed, 156 were diagnosed with suspected peritonitis using NGALlab and ISPD criteria. Each sample underwent analyses with both NGALlab and NGALds. As depicted in Fig. 1, NGALds exhibited a robust correlation with NGALlab categories (Rs = 0.876, P &lt; 0.001), accurately identifying 96% (150 out of 156) of peritonitis cases. Discrepancies between NGALlab and NGALds were most evident when NGAL values exceeded the 600 μg/L threshold. Nevertheless, these variations did not impact clinical significance, as both methods consistently diagnosed elevated NGAL values indicative of peritonitis.
After ROC analysis, which yielded an AUC of 0.82 (p &lt; 0.001) (Fig. 2), the Youden Index was employed to identify a threshold value of 100 μg/L for the diagnosis of suspected peritonitis. Importantly, the application of this threshold to NGALds demonstrated a positive predictive value of 0.64 and a negative predictive value of 0.87.

Conclusion
In conclusion, our study reinforces the significant correlation between NGAL values obtained through the laboratory standard (NGALlab) and the novel NGAL dipstick test (NGALds). Notably, NGALds exhibited high efficacy, accurately identifying 96% of peritonitis cases diagnosed by NGALlab. This robust performance positions the NGAL dipstick as a valuable and accessible alternative for rapid assessment in patients exhibiting symptoms indicative of peritonitis. The user-friendly attributes of NGALds not only make it a practical diagnostic tool but also a patient-centric one.
Furthermore, the high negative predictive value provides confidence in considering NGALds as a frontline diagnostic tool for suspected peritonitis. The ease of use and prompt results open a promising avenue for improving clinical workflows, offering an opportunity for expedited and efficient peritonitis diagnosis. For instance, NGALds could find utility in centres where NGAL is unavailable in the laboratory or at the patient's home.