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Age-related changes in 24-hour urine composition must be considered in the medical management of nephrolithiasis.

BACKGROUND AND PURPOSE
Over the past 50 years, there has been an upward shift in the age of peak incidence of stone disease, yet less is known regarding how the urinary biochemical profile changes with aging. Therefore, we sought to examine the relationship between age and 24-hour urine composition.


METHODS
We retrospectively reviewed a database of our tertiary care stone clinic patients seen from March 2002 to February 2012. Analysis of pretreatment 24-hour urine collections across age groups was performed using univariate analysis of variance and multivariate linear regression models adjusting for clinical and demographic factors and 24-hour urine parameters.


RESULTS
A total of 1115 patients were broken down into age groups consisting of <45 years (221; 19.7%), 45-54.9 years (270; 23.8%), 55-64.9 years (270; 24.6%), and ≥65 years (356; 31.9%). Univariate analysis found significant ascending trends with aging for mean body mass index, while mean urine pH, 24-hour calcium, uric acid (UA), ammonium, creatinine, and supersaturation (SS) of calcium oxalate (CaOx) and calcium phosphate (CaP) decreased with age (all P for trend <0.05). Adjusted multivariate analysis demonstrated that increased age was significantly associated with increased 24-hour citrate and SS UA, whereas increased age was significantly associated with decreased pH, 24-hour UA, creatinine, SS CaOx, and SS CaP (all P for trend <0.05).


CONCLUSIONS
There are numerous age-related changes in the metabolic profile as seen on 24-hour urine collection. This highlights the importance of evaluating stone-forming patients of all ages with 24-hour urine collections because both the type and degree of metabolic abnormality may change with age.