Procalcitonin levels in chronic kidney disease and determination of a new threshold value

Aim: The aim of this study is to retrospectively compare procalcitonin (PCT), C-reactive protein (CRP), and white blood cell (WBC) levels between patients with chronic kidney disease (CKD) without signs of infection and age- and sex-matched healthy controls. Additionally, this study seeks to establish a clinically more accurate threshold value for PCT in end-stage CKD patients, enhancing its reliability as an infection biomarker and minimizing unnecessary antibiotic use. Material and Method: In this study, PCT, CRP, and WBC levels were retrospectively compared among 100 healthy individuals and 100 patients in each stage of CKD, including Stage 1-2, Stage 3, Stage 4, and Stage 5. Additionally, 100 Stage 5 CKD patients with infection and 100 without infection were prospectively evaluated. PCT levels were measured using the ELISA method, and ROC curve analysis was performed to determine the optimal threshold value for Stage 5 CKD patients. Results: In the retrospective analysis, a one-way analysis of variance was performed to evaluate differences in mean age among healthy individuals and patients with different stages of CKD, revealing no statistically significant differences between groups (p = 0,474). The Kruskal-Wallis test conducted for eGFR (estimated glomerular filtration rate), PCT, CRP, and WBC levels showed statistically significant differences among all groups (p <0,001). According to the Bonferroni-adjusted Mann-Whitney U test, eGFR levels significantly differed among all groups (p <0,001). In terms of PCT levels, no significant difference was observed between healthy individuals and Stage 1-2 CKD patients (p = 0,999), whereas a significant difference was found between Stage 1-2 and Stage 3 CKD patients (p = 0,030). PCT levels increased significantly from Stage 3 onward, with statistically significant elevations in Stage 4 (p = 0,001) and Stage 5 (p = 0,010). Regarding CRP levels, there was no significant difference between healthy individuals and Stage 1-2 or Stage 3 CKD patients (p = 0,999); however, a significant increase was observed in Stage 4 compared to healthy individuals and Stage 1-2 CKD patients (p = 0,004). Although no significant difference was detected between Stage 5 and Stage 4 CKD patients (p = 0,100), CRP levels in Stage 5 were notably higher than in earlier stages. For WBC levels, no significant difference was found among healthy individuals, Stage 1-2, Stage 3, and Stage 4 CKD patients (p >0,05). However, Stage 5 CKD patients exhibited a significant decrease in WBC levels compared to healthy individuals and early-stage CKD patients (p <0,05). Spearman correlation analysis across all groups revealed a strong negative correlation between eGFR and PCT (r = −0,697, p <0,001) and between eGFR and CRP (r = −0,314, p <0,001), while a positive correlation was observed between eGFR and WBC (r = 0,206, p <0,001). Within individual group analyses, no significant correlation was found between eGFR and PCT, CRP, or WBC in healthy individuals (p >0,05). In Stage 1-2 CKD patients, a negative correlation was observed between eGFR and WBC (r = −0,240, p = 0,016), whereas in Stage 3 CKD patients, eGFR and PCT levels showed a negative correlation (r = −0,251, p = 0,012). No significant correlation was found between eGFR and PCT, CRP, or WBC in Stage 4 and Stage 5 CKD patients (p >0,05). In the prospective analysis, chi-square and t-test results indicated no significant differences in age and sex between infected and non-infected Stage 5 CKD patients (p = 0,777, p = 0,220). According to the Mann-Whitney U test, eGFR levels did not significantly differ between the two groups (p = 0,190), whereas PCT levels were significantly higher in the infected group (p <0,001). The ROC analysis performed in Stage 5 CKD patients identified an optimal PCT threshold of 0,74 ng/mL for distinguishing infection. At this cutoff value, the test demonstrated 90% sensitivity and 90% specificity, with both positive and negative predictive values calculated as 90%. The area under the curve (AUC) was 0,953, indicating that PCT has a high diagnostic accuracy in detecting infection in CKD patients. Conclusion: This study demonstrates that PCT and CRP levels significantly increase in the advanced stages of CKD, while WBC levels decrease in later stages, and eGFR progressively declines as the disease progresses. Notably, PCT levels were found to be significantly elevated in association with both infection and renal function decline. The ROC analysis results from our study indicate that, in clinical practice, a higher PCT threshold (0,74 ng/mL) should be considered for the early diagnosis and management of infections.