Sex and Age Variation for Nephrolithiasis Risk Factors on 24-Hour Urine Metabolic Evaluation: A Real-World Single-center Retrospective Analysis.

Objectives: To determine how age and sex relate to metabolic abnormalities in stone-forming patients, while quantifying risk variation across groups, given the influence of demographic factors on 24-hour urine analytes.

Methods: All 24-hour urine collections for nephrolithiasis evaluated at our institution between 2004-2020 were retrospectively reviewed. Only the first, pre-treatment Litholink™ urine collection per patient was included. Patients were stratified by sex and age (<50, 50-65, >65 years), and analytes were evaluated using multivariable linear regression with sex, age, and BMI as predictors. Abnormal thresholds were based on LabCorp® sex-specific ranges. High urine pH (>6.8), urea nitrogen (UUN24), and sulfate (Sul24) were included in secondary analyses.

Results: Of 4216 initial collections, 2131 met inclusion criteria after exclusions based on cystinuria, duplicate or follow-up studies, and Cr24/kg-based under- or over-collection. The cohort was 50.0% female, 50.0% male; mean (SD) age was 56.5 (15) years and BMI 26.8 (5.6) kg/m². Males showed higher 24-hour oxalate, sodium, uric acid, urea nitrogen, and sulfate. Females exhibited higher calcium and higher urine pH. Younger patients had higher calcium phosphate supersaturation and urine calcium, while older patients had more acidic urine.

Conclusions: Sex and age are independently associated with urine analyte values and stone risk. Male and younger patients are more likely to exhibit diet-driven abnormalities, whereas females and older patients present with risks linked to intrinsic physiology. These findings enhance the understanding of patient-specific stone risk and support tailored approaches to evaluation and prevention.