Normal Variability of Urinary Markers in Individuals with Spinal Cord Injury and Disease Using Intermittent Catheterization

Accurate diagnosis of urinary tract infection (UTI) in individuals with neurogenic lower urinary tract dysfunction (NLUTD) due to spinal cord injury or disease (SCI/D) remains a major clinical challenge. Standard diagnostic tools--including urine dipstick, urinalysis, and culture--lack population-specific reference ranges, and existing criteria are often insufficient to distinguish infection from background variability. To address this gap, we conducted a longitudinal study to define the range of "normal" variability in common urinary biomarkers among individuals with SCI/D who manage their bladders using intermittent catheterization (IC). Participants with NLUTD due to SCI/D who manage their bladders with IC provided urine samples at least two weeks apart, while asymptomatic. We assessed urinary white blood cell count, nitrite, leukocyte esterase, culture-based findings, and urine neutrophil gelatinase-associated lipocalin (uNGAL) to characterize intra-individual stability and inter-individual variation in biomarker profiles. Findings demonstrate that urine parameters exhibit measurable but bounded variability in the absence of UTI, and that deviations beyond these thresholds may support more accurate and individualized UTI diagnosis. By defining the normal range within which values vary without the emergence of symptoms, we hope to further inform clinical and researcher decision-making around variability that moves an individual beyond their normal range of variation in these urinary markers. Operationalizing biologic variability can reduce diagnostic uncertainty and improve antimicrobial stewardship in this frequently overtreated population.