Beware the low urine pH--the major cause of the increased prevalence of nephrolithiasis in the patient with type 2 diabetes.

There is an increased prevalence of nephrolithiasis and an increase in the incidence of renal colic in patients with diabetes, obesity, hypertension and insulin resistance because of an increased frequency of uric acid crystallization. Uric acid crystallization occurs in the milieu of an acid urine and is not due to hyperuricosuria as with insulin resistance, urinary uric acid levels are generally decreased because of increased renal tubular reabsorption. However, in the presence of insulin resistance, there is decreased renal tubular generation of ammonia and increased sodium absorption leading to acidification of the urine and uric acid crystallization. The presence of a low urine pH should alert the clinician to the increased risk of nephrolithiasis particularly in the obese, diabetic or hypertensive patient. Prevention of nephrolithiasis can be achieved in susceptible individuals either by alkalizing the urine and/or by further decreasing the uric acid content of the urine with a xanthine oxidase inhibitor such as allopurinol.