Associate Professor of Pediatrics WVU Charleston Campus Charleston, West Virginia, United States
Background: Pediatric nephrolithiasis is frequently associated with comorbid conditions, including epilepsy, paralysis, and gastrointestinal and metabolic disorders. Therefore, medically complex children (MCC) are a unique population are at risk to experience significant morbidity related to nephrolithiasis. Calcium phosphate in particular stones are commonly found in MCC receiving enteral feeds. Objective: The objective of this study is to investigate the etiology for calcium phosphate stones in this patient population. Design/Methods: This is a retrospective cohort study of gastrostomy fed, MCC who presented to a high-volume Pediatric Stone Center from 2015 to 2019. MCC were defined as those with a diagnosis of cerebral palsy and/or severe developmental delay who were non-ambulatory. A control group was composed of newly presenting patients to the stone clinic without comorbid conditions. Twenty-four hour urine collections were performed prior to medical intervention and were compared between MCC and controls. Results: Twenty-four MCC children were compared to 38 controls. The median age (interquartile range, [IQR]) and weight of MCC were 11.9 (7.5, 16.3) years and 28.6 (21.0, 37.0) kg. Urine supersaturation of calcium phosphate (SSCaP) was similar in MCC and controls (1.7 and 2.0, p=0.41). Weight-based 24-hour urine calcium and phosphorus excretion were also similar in MCC and controls. The median BSA-adjusted urine volume was significantly higher in MCC vs controls (2.2 vs. 1.2 L/1.73m2, p< 0.001), which contributed to lower 24-hour average urinary phosphorus (271.9 vs. 689.7 mg/L, p< 0.001) and calcium concentrations (73.3 vs. 132.8 mg/L, p< 0.001). However, urine pH was significantly higher in MCC (7.4 vs. 6.3, p< 0.001), as was net gastrointestinal absorption of alkali (1.1 vs. 0.3 mEq/kg/day, p< 0.001). In regression analysis, SSCaP increased by a factor of 2.81 for every 1-unit increase in urine pH (p < 0.001).
Conclusion(s): A high urine pH is associated with an increased risk of calcium phosphate nephrolithiasis in MCC. This may reflect a higher alkaline content of enteral feeding formulations compared to children on a standard American diet.
