Risk factors for urolithiasis in children on the ketogenic diet

Kidney stones have been associated with use of the ketogenic diet in childr en with refractory seizure disorders. We performed a case-control study exa mining risk factors for the development of stones on the ketogenic diet, an d prospectively followed children initiating the ketogenic diet to evaluate the incidence of urolithiasis. Clinical characteristics of 18 children pre senting with stones (8 uric acid stones, 6 mixed calcium/uric acid stones, 1 calcium oxalate/phosphate stone, 3 stones not evaluated) were compared wi th characteristics of non-stone-forming children initiating the ketogenic d iet at Johns Hopkins since July 1996. Since July 1996, 112 children initiat ing the ketogenic diet have been followed for development of stones. Follow -up times on the diet range from 2 months to 2.5 years. Of 112 children, 6 have developed stones (3 uric acid, 3 mixed calcium/uric acid stones) (0.8 children developing stones/100 patient-months at risk). Comparisons of chil dren presenting with stones on the ketogenic diet with characteristics of t he entire cohort initiating the ketogenic diet suggest younger age at diet initiation and hypercalciuria are risk factors for the development of stone s. Prospective evaluation of children initiating the ketogenic diet reveale d that almost 40% of patients had elevated fasting urine calcium: creatinin e ratios at baseline; this increased to 75% after 6 months on the diet. Med ian urine pH was 5.5 at diet initiation, and remained at 6.0 thereafter. In a subset of patients tested, urinary citrate excretion fell from a mean of 252 mg/24 h pre diet initiation to 52 mg/24 h while on the diet. Uric acid excretion remained normal. Patients maintained on the ketogenic diet often have evidence of hypercalciuria, acid urine, and low urinary citrate excre tion. In conjunction with low fluid intake, these patients are at high risk for both uric acid and calcium stone formation.