24-Hour Urinary Chemistries and Kidney Stone Risk

Area of Science:

• Nephrology
• Urology
• Biochemistry

Background:

• Kidney stones are a prevalent condition with a high recurrence rate.
• Previous research on urinary factors and kidney stone risk often assumed linear relationships or used arbitrary thresholds.
• The hierarchy of effects for various urinary parameters on stone formation remains incompletely understood.

Purpose of the Study:

• To evaluate the independent associations between specific urine chemistries and kidney stone formation.
• To examine the magnitude and shape (linear vs. nonlinear) of these associations.
• To determine the relative importance of different urinary factors in kidney stone risk.

Main Methods:

• Analysis of 9,045 24-hour urine collections from 6,217 participants in large prospective cohort studies.
• Multivariable logistic regression with restricted cubic splines to model potentially nonlinear relationships.
• Optimal inflection point and dominance analyses to identify thresholds and relative importance of urinary factors.

Main Results:

• Most urinary factors, except urine pH, were significantly associated with kidney stone risk.
• Higher urinary calcium, oxalate, phosphorus, and sodium correlated with increased stone risk.
• Higher urine volume, uric acid, citrate, potassium, and magnesium correlated with decreased stone risk.
• Relationships were largely linear for urine calcium, uric acid, and sodium, with some attenuation above inflection points for others.
• Dominance analysis ranked calcium, volume, and citrate as most important, followed by oxalate, potassium, and magnesium, then uric acid, phosphorus, and sodium.

Conclusions:

• Urine chemistries exhibit complex, non-uniform relationships with kidney stone formation.
• Differential relative associations and magnitudes of effect exist among urinary factors.
• These findings provide a more nuanced understanding of urinary risk factors for kidney stones.