Importance of secretory leukocyte protease inhibitor (SLPI) as a potential diagnostic marker for UTI diagnosis

Background and objectives. Early diagnosis of urinary tract infection (UTI) and appropriate treatment are essential to prevent complications. As there is no single specific test for diagnosis, there is a need to develop more reliable biomarkers to improve diagnostic accuracy. Secretory leukocyte protease inhibitor (SLPI) has been documented to have important role in UTI. The aim of this study is to evaluate the importance of serum SLPI as biomarker for the diagnosis of UTI. Materials and methods. A case-control study was conducted involving 140 females, divided into two equal groups: 70 patients with UTI and 70 apparently healthy females, among control group of whom 28 had asymptomatic bacteriuria (ABU) and 42 had sterile urine cultures. Participants were aged between 18 and over 58 years. Both urine and blood samples were collected for general urine examination, bacteriological urine culture, and measurement of serum SLPI using the ELISA technique. Results. No statistically significant difference was found in serum SLPI levels between UTI patients and controls (mean: 390.58 ng/L vs. 390.35 ng/L, p = NS). Higher SLPI levels were observed in healthy females aged 18-37 and those who were overweight. Urine cultures revealed bacterial growth in 57.14% of UTI patients and 40% of controls (ABU cases), with E. coli being the most common isolate in both groups. Notably, the highest mean of SLPI levels were associated with S. epidermidis in UTI patients and with E. coli in ABU cases. Receiver operating characteristic (ROC) analysis revealed that serum SLPI had low discrimination power to detect UTI (AUC = 0.542; 95% CI: 0.446-0.638). Conclusions. The absence of significant difference in serum SLPI levels between UTI patients and controls may be due to the absence of systemic inflammation and reflects the potential role of SLPI in the innate immune response. Further studies are required to evaluate the clinical utility of SLPI in specific patient subgroups or combined with other biomarkers.