# The impact of urine pH on lithogenic risk profile in children with urolithiasis

## TL;DR

This study shows that urine pH affects stone risk in children, with optimal pH between 6.75 and 7.0 helping to prevent kidney stones.

## Contribution

The study reveals how urine pH interacts with metabolic factors to influence lithogenic risk in pediatric urolithiasis.

## Key findings

- Children with stones had higher urine volume, oxalate, calcium, and uric acid compared to controls.
- Lower urine pH was linked to higher BMI and reduced urine volume in stone-formers.
- Citrate and magnesium excretion increased at pH 6.75–7.0, suggesting a protective effect.

## Abstract

Urinary pH is known to influence the solubility and excretion of lithogenic substances, yet its relationship with other metabolic parameters in pediatric stone formers remains underexplored. This study investigated the association between urinary pH and lithogenic risk factors in children and adolescents with urolithiasis compared to healthy controls.

A total of 400 pediatric patients (ages 3–18 years) with urinary stones and 372 age- and sex-matched healthy controls were included. All participants completed a 24-h urine collection for comprehensive metabolic analysis. Parameters assessed included urinary pH, BMI z-score, urine volume, osmolality, excreted creatinine, GFR, and urinary excretion of calcium, ionized calcium, oxalate, phosphate, magnesium, citrate, and uric acid. Two lithogenic risk indices were also evaluated: Bonn Risk Index (BRI) and Upper Metastable Limit osmolality (UMLOsm).

Stone-formers demonstrated significantly higher urine volume, oxalate, calcium, ionized calcium, uric acid, and BRI compared to controls. In contrast, controls exhibited higher levels of urinary citrate, osmolality, and UMLOsm. Lower urine pH was associated with higher BMI z-scores and reduced urine volume. Calcium excretion increased with urine pH up to 7 before declining, whereas citrate and magnesium excretion rose at pH levels between 6.75 and 7.0, indicating a potential protective effect.

Our findings highlight the importance of individualized dietary and lifestyle guidance in pediatric stone formers, with a focus on maintaining a healthy BMI, adequate hydration, and urine pH between 6.75 and 7.0 to support protective factors like citrate and magnesium.

A higher resolution version of the Graphical abstract is available as Supplementary information

A higher resolution version of the Graphical abstract is available as Supplementary information

The online version contains supplementary material available at 10.1007/s00467-025-07044-1.