The high fat, low carbohydrate ketogenic diet is increasingly used for management of difficult to control seizures. In recent years 4 patients with stones on the ketogenic diet have been reported (3 uric acid and 1 mixed calcium phosphate, calcium oxalate stone). We have recently seen 11 additional patients of approximately 100 on the ketogenic diet, who developed microscopic or gross hematuria. Five patients, all with gross hematuria, had renal stones. Two of the stones were mixed calcium phosphate, calcium oxalate stones. Three stones were uric acid stones. Ten of the 11 patients who developed hematuria on the ketogenic diet had evidence of hypercalciuria (urine calcium:creatinine>0.2) on a fasting spot urinalysis.

To further evaluate this phenomenon, we are now prospectively screening all patients embarking on the ketogenic diet for the development of hematuria and hypercalciuria. In this prospective study, half of the patients (n=2) had hypercalciuria prior to embarking on the diet. After 3 months on the diet, an additional patient developed hypercalciuria, and another maintained normal calcium excretion on the diet.

Low urinary flow rates, low urine pH, and hypercalciuria probably contribute to kidney stone formation in children on the ketogenic diet. Physicians placing children on the ketogenic diet should be aware of this potential complication and screen for it.