STONE DISEASE

Type 2 Diabetes Increases the Risk for Uric Acid Stones
Daudon M, Traxer O, Conort P, Lacour B, Jungers P
Assitance Publique-Hopitaux de Paris, Laboratoire de Biochimie A, Hopital Necker-Enfants Malades, Paris, France
J Am Soc Nephrol. 2006; 17: 2026-33

• An increased prevalence of nephrolithiasis has been reported in patients with diabetes. Because insulin resistance, characteristic of the metabolic syndrome and type 2 diabetes, results in lower urine pH through impaired kidney ammoniagenesis and because a low urine pH is the main factor of uric acid (UA) stone formation, it was hypothesized that type 2 diabetes should favor the formation of UA stones. Therefore, the distribution of the main stone components was analyzed in a series of 2464 calculi from 272 (11%) patients with type 2 diabetes and 2192 without type 2 diabetes. The proportion of UA stones was 35.7% in patients with type 2 diabetes and 11.3% in patients without type 2 diabetes (P < 0.0001). Reciprocally, the proportion of patients with type 2 diabetes was significantly higher among UA than among calcium stone formers (27.8 versus 6.9%; P < 0.0001). Stepwise regression analysis identified type 2 diabetes as the strongest factor that was independently associated with the risk for UA stones (odds ratio 6.9; 95% confidence interval 5.5 to 8.8). The proper influence of type 2 diabetes was the most apparent in women and in patients in the lowest age and body mass index classes. In conclusion, in view of the strong association between type 2 diabetes and UA stone formation, it is proposed that UA nephrolithiasis may be added to the conditions that potentially are associated with insulin resistance. Accordingly, it is suggested that patients with UA stones, especially if overweight, should be screened for the presence of type 2 diabetes or components of the metabolic syndrome.
  
  
• Editorial Comment
  As obesity, the metabolic syndrome and type 2 diabetes increase in prevalence in the Western world, newly recognized associated morbidities continue to increase the impact on patients and healthcare. This article demonstrates a strong link between uric acid urolithiasis and type 2 diabetes. The hypothesis rests in the lower urine pH noted in type 2 diabetes predisposing to uric acid stone formation. The authors combined calcium oxalate and calcium phosphate stones into one group: “calcium-stones”, though calcium oxalate stones are predisposed to formation in more acidic urine while calcium phosphate stones are predisposed to formation in more alkaline urine. A repeat analysis separating these two stone compositions may be of benefit. In the small group of patients (25) with type 2 diabetes who underwent urinary evaluations, the urine pH was comparable to patients without diabetes who formed uric acid stones, raising questions regarding the validity of the hypothesis proposed. Though the pathophysiology may not be clear, the 7-fold risk of a uric acid stone composition in type 2 diabetes suggests a strong link, and supports the recommendation that uric acid stone formers be screened for the metabolic syndrome.

Dr. Manoj Monga
Professor, Department of Urology
University of Minnesota
Edina, Minnesota, USA