April 12, 2016
The Journal of Urology
TAKE-HOME MESSAGE
- Obesity is a known risk factor for the development of urinary stone disease, with the observed incremental risk largely driven by decreases in urine pH. The authors of this study retrospectively evaluated response to potassium citrate, stratified by BMI, among individuals with hypocitraturia and low urine pH. They found that increasing BMI was associated with an attenuated response to potassium citrate therapy with respect to both urine pH and urine citrate levels, necessitating more frequent dose adjustments among individuals with higher BMI.
- Obese individuals may mount a less robust response to potassium citrate therapy and require closer monitoring. Whether the observed heterogeneity of treatment effect translates into clinically meaningful differences between normal-weight and obese individuals remains unknown.
Urology
Written by Brian R Matlaga MD, MPH
The interplay between obesity and stone disease is complex. It has been well established that obesity carries with it an increased risk for stone formation. However, the precise reason for this relationship is not well understood: is it driven by dietary factors, is it a complex renal pathology that elicits lithogenic changes to the urine chemistry, or is it some combination thereof? The present manuscript from the Duke urology group nicely broadens our understanding of obesity and the management of patients with metabolic risk factors for stone formation. In short, the authors found that obese patients did not respond as well to potassium citrate therapy, and this response became more blunted as body mass index (BMI) increased. In addition, the authors found that, among patients with a higher BMI, more frequent medication adjustments were required.
There are two important take-aways from these findings. First, this study contributes to our understanding of kidney stone risk factors among the obese. Although it is not clear for what reason increasing obesity resulted in decreasing effectiveness of a potassium citrate dosage, this finding will inform future research efforts going forward. Perhaps it is related to insulin resistance and low urinary pH, both of which are present to a greater extent among obese stone-formers. From a practical standpoint, though, this study will also serve to improve clinical care. For those of us who take care of obese stone-formers, the findings presented herein suggest that more frequent metabolic surveillance of the obese patients receiving potassium citrate will be beneficial, as those patients with particularly elevated BMI are at greater risk for medication adjustment and escalation.
Abstract
PURPOSE
Obesity has been shown to be a risk factor for kidney stone formation. Obesity leads to insulin resistance which subsequently leads to low urinary pH. Low urinary pH is typically treated with potassium citrate. We determined if the response to potassium citrate for the treatment of low urinary pH and hypocitraturia varied when patients were stratified by body mass index.
MATERIALS AND METHODS
We retrospectively reviewed the records of patients with urolithiasis and concomitant hypocitraturia and low urinary pH as unique abnormalities upon metabolic evaluation treated exclusively with potassium citrate. Based on body mass index the cohort was divided into the 4 groups of normal weight, overweight, obese and morbidly obese. Metabolic data were compared among the 4 groups at baseline and subsequent followup visits up to 2 years. We compared urinary pH and citrate in absolute values and the relative changes in these parameters from baseline. Similarly, we compared the rates of potassium citrate treatment failure.
RESULTS
A total of 125 patients with hypocitraturia and low urinary pH were included in this study. Median patient age was 61 years, 80 patients were male and median body mass index was 30.4 kg/m(2). Patients with a higher body mass index tended to be younger (p=0.010), and had a lower urinary citrate but higher sodium, oxalate and uric acid levels. Urinary pH was similar across body mass index groups. pH values and their absolute changes from baseline were lower as body mass index increased (p ≤0.001). Similarly, we noted an association between increasing body mass index category and lower urinary citrate levels accompanied by a statistically significant trend indicating lower absolute changes in citrate with increasing body mass index (p ≤0.001). Potassium citrate dose was increased more frequently among the higher body mass index groups.
CONCLUSIONS
Patients with a higher body mass index presented with a lower increase in citrate excretion and urinary pH levels after they were started on potassium citrate, and they needed more frequent adjustments to their therapy.