Association Between Urine pH on ICU Day 1 and 90-Day Mortality in Sepsis: A Retrospective Cohort Study

Abstract

Introduction: Urine pH is an easily obtainable bedside indicator of urinary acidification; however, its prognostic value in sepsis remains unclear.

Aim of the study: We investigated the association between urine pH measured on intensive care unit (ICU) Day 1 and 90-day mortality in patients with sepsis.

Material and methods: This single-center retrospective cohort study was conducted at Shiga University of Medical Science Hospital between August 2011 and April 2023. Adult ICU patients with sepsis who had urine pH measured on ICU Day 1 were included. Urine pH was assessed using dipstick colorimetry, and the earliest value within 12 h of ICU admission was analyzed. The primary outcome was 90-day all-cause mortality. Associations were evaluated using multivariable Cox proportional hazards models.

Results: Among 468 patients (median age 72 years; 61.8% male), the 90-day mortality rate was 25.6%. Spline analysis showed no evidence of nonlinearity (P=0.331). Each 0.5-unit increase in Day-1 urine pH was associated with lower 90-day mortality (adjusted hazard ratio [HR] 0.572; 95% confidence interval [CI] 0.422–0.776; P<0.001). Mortality was 30.2% in patients with urine pH ≤6.0 and 11.4% in those with urine pH >6.0; higher urine pH remained associated with lower mortality risk after adjustment (adjusted HR 0.279; 95% CI 0.147–0.529; P<0.001). Urine pH on ICU Days 2 or 3 was not significantly associated with mortality.

Conclusions: Lower urine pH on ICU Day 1 was independently associated with increased 90-day mortality in sepsis, suggesting that urine pH may complement early risk stratification in critically ill patients.