Quantifying the Relationship Between Renal Function and Procalcitonin: A Study of 14 431 Blood Cultures.

Background: Negative procalcitonin (PCT) values may decrease suspicion for bacterial bloodstream infections among patients presenting with symptoms of infection; however, the reliability of PCT in patients with renal dysfunction remains poorly characterized. We quantified the relationship between estimated glomerular filtration rate (eGFR) and positive PCT values in patients with suspected bacterial bloodstream infections. Methods: We conducted a retrospective cohort study of 2,832 patients with 14 431 blood cultures at a Veterans Affairs Medical Center (2016-2024). PCT values within 48 hours of culture were analyzed across eGFR categories based on chronic kidney disease staging. We used multivariate logistic regression to assess the relationship between eGFR and positive PCT (≥0.5 ng/mL), adjusting for age and race. Results: Among 14 431 blood cultures, 1417 (9.8%) were positive. When cultures were positive, the proportion of positive PCT values was 47.0% with normal renal function (eGFR ≥90 mL/min/1.73m²) and 91.7% in severe renal dysfunction (eGFR 0-14.9 mL/min/1.73m²). When cultures were negative, the proportions of positive PCT values were 27.6% and 84.0%, respectively. For each lower eGFR category, the odds of a positive PCT value were 40-43% higher (OR 1.40 for positive cultures, 1.43 for negative cultures), after adjusting for age and race. This inverse relationship was consistent across multiple PCT thresholds (0.25-1.50 ng/mL). Conclusions: This large-scale analysis uncovers an inverse relationship between renal function and positive PCT values in patients both with and without culture-positive bloodstream infections. The discriminatory power of PCT for bloodstream infection diminishes in patients with impaired renal function.