Subsequent urinary stone events are predicted by the magnitude of urinary oxalate excretion in enteric hyperoxaluria
Authors: D’Costa Matthew R , Kausz Annamaria T , Carroll Kevin J , Ingimarsson Jóhann P , Enders Felicity T , Mara Kristin C , Mehta Ramila A , Lieske John C 
Published: October 2020

Abstract

Data directly demonstrating the relationship between urinary oxalate (UOx) excretion and stone events in those with enteric hyperoxaluria (EH) are limited. Therefore, we assessed the relationship between UOx excretion and risk of kidney stone events in a retrospective population-based EH cohort. In all, 297 patients from Olmsted County, Minnesota were identified with EH based upon having a 24-h UOx ≥40 mg/24 h preceded by a diagnosis or procedure associated with malabsorption. Diagnostic codes and urologic procedures consistent with kidney stones during follow-up after baseline UOx were considered a new stone event. Logistic regression and accelerated failure time modeling were performed as a function of UOx excretion to predict the probability of new stone event and the annual rate of stone events, respectively, with adjustment for urine calcium and citrate. Mean ± standard deviation age was 51.4 ± 11.4 years and 68% were female. Median (interquartile range) UOx was 55.4 (46.6–73.0) mg/24 h and 81 patients had one or more stone event during a median follow-up time of 4.9 (2.8–7.8) years. Higher UOx was associated with a higher probability of developing a stone event (P &lt; 0.01) and predicted an increased annual risk of kidney stones (P = 0.001). Estimates derived from these analyses suggest that a 20% decrease in UOx is associated with 25% reduction in the annual odds of a future stone event. Thus, these data demonstrate an association between baseline UOx and stone events in EH patients and highlight the potential benefit of strategies to reduce UOx in this patient group.

Background
Data directly demonstrating the relationship between urinary oxalate (UOx) excretion and stone events in those with enteric hyperoxaluria (EH) are limited.

Methods
We assessed the relationship between UOx excretion and risk of kidney stone events in a retrospective population-based EH cohort. In all, 297 patients from Olmsted County, Minnesota were identified with EH based upon having a 24-h UOx ≥40 mg/24 h preceded by a diagnosis or procedure associated with malabsorption. Diagnostic codes and urologic procedures consistent with kidney stones during follow-up after baseline UOx were considered a new stone event. Logistic regression and accelerated failure time modeling were performed as a function of UOx excretion to predict the probability of new stone event and the annual rate of stone events, respectively, with adjustment for urine calcium and citrate.

Results
Mean ± SD age was 51.4 ± 11.4 years and 68% were female. Median (interquartile range) UOx was 55.4 (46.6–73.0) mg/24 h and 81 patients had ≥1 stone event during a median follow-up time of 4.9 (2.8–7.8) years. Higher UOx was associated with a higher probability of developing a stone event (P &lt; 0.01) and predicted an increased annual risk of kidney stones (P = 0.001). Estimates derived from these analyses suggest that a 20% decrease in UOx is associated with 25% reduction in the annual odds of a future stone event.

Conclusions
These data demonstrate an association between baseline UOx and stone events in EH patients and highlight the potential benefit of strategies to reduce UOx in this patient group.