## 4 Discussion  
In this investigation, we analyzed NGALds as a rapid NGAL assay in PDE using semi-quantitative colorimetric-category test strips. In particular, we theorized that the results of this new method could be similar to the results of the quantitative peritoneal laboratory-based NGAL test and could be coherent to the present biomarkers used to evaluate peritonitis and inflammation. In particular, we speculated that NGALds may be useful in the determination of peritonitis. In fact, it was proved that the early identification and prompt management of peritonitis is fundamental to limiting the structural and functional changes and avoiding peritoneal membrane malfunction in peritoneal dialysis patients [14]. At the state of the art, clinical criteria for the identification of peritonitis consist of clinical signs and symptoms, cloudy effluent, and positive culture [10]. Nevertheless, these features may not always be notable in the timely recognition of peritonitis. For this reason, numerous biomarkers have been investigated in the setting of early diagnosis of peritonitis such as adipokine [15], matrix-metalloproteinase-9 [16], and various cytokines [17]. Unfortunately, none of them seems to have applicability in clinical practice. Instead, the NGAL value in plasma and peritoneal effluent has been gaining increasing attention in the last decades and the quantitative peritoneal laboratory-based NGAL test has already been proved to be a helpful instrument for the timely and precise diagnosis of peritonitis [7; 9]. Recently, NGALds has been developed as a POCT assay for NGAL rapid evaluation and several studies have demonstrated that it performs uniformly to the quantitative-continuous assay in urine biological fluids. These studies were all performed on patients with AKI [18; 19; 20]. In our study, we evaluated NGALds using the peritoneal effluent as a biological sample from PD patients with and without peritonitis. In accordance with the aforementioned data reported in urine samples, the current results have confirmed that, also in peritoneal effluent, the results of the peritoneal NGALds are coherent with the laboratory-based NGAL values. Furthermore, our results highlighted a good positive correlation between the peritoneal NGALds and laboratory parameters involved in peritonitis. In particular, we observed a robust positive correlation between peritoneal NGALds and the white cell count in PDE, the main laboratory parameter for the peritonitis diagnosis suggested by the ISPD guidelines. Furthermore, the peritoneal NGALds levels resulted in being significantly elevated in PD patients with peritonitis. These results corroborate that NGAL is implicated in the human immune response and that it is promptly measurable in PDE at the beginning of peritonitis, even if detected with a semi-quantitative color-categorized assay. Figure 2: Comparison between NGALds assay and laboratory-based NGAL (turbidimetric immunoassay) in terms of time. Thirty (=total number of patients enrolled in the study) determinations for each assay. The peritoneal NGAL quantitative values fit well with the peritoneal NGALds categories. This observation confirmed that both methods can be mixed with the white cell count in PDE, as an extra tool for the diagnosis of peritonitis [8]. In addition, we observed that all the PD patients with the diagnosis of peritonitis had peritoneal NGALds values \(\geq\) 300 ng/dL. Similarly, all the PD patients with white cell count \(\geq\) 100 \(\times\) 10\({}^{6}\)/L and with peritoneal laboratory-based NGAL \(\geq\) 200 ng/dL had peritoneal NGALds values \(\geq\) 300 ng/dL. Consequently, we suggest that the indicative cut-off point of NGALds for peritonitis could be the value of 300 ng/mL. The NGALds assay is completed within a median time of 20 min, while the laboratory-based NGAL test requires a median time of 65 min. We spent significantly less time using NGALds compared to the laboratory-based test.