Hospitalization for kidney stones in the Inflammatory Bowel Disease (IBD) population is common, particularly among Crohn's patients who had a small bowel resection. This patient population experiences a lifetime occurrence of kidney stone formation as high as 25% accompanied with a high rate of recurrence (the typical rate of stone formation is ~10% in the non IBD population). Giving oral calcium is used to bind oxalate in the intestine in an attempt to reduce the amount of oxalate that is absorbed into the body and to reduce urinary oxalate levels. However, there are no defined guidelines for the optimum dosing of calcium. This study's primary objective is to scientifically define an appropriate range of calcium supplementation that reduce the level of oxalate found in the urine of patients living with inflammatory bowel disease.

The primary objective of this study is to establish optimal oral calcium supplementation in Crohn's patients who have had an ileal bowel resection. This population is at high risk for calcium oxalate kidney stones, a direct consequence of extensive gut malabsorption and enteric hyperoxaluria. The benefit of providing oral calcium in this patient population (as a means to reduce intestinal oxalate absorption) is known, however, there are no appropriate targets for calcium dosing, which is presently performed empirically or not at all. Our goal is to establish simple, safe and practical guidelines for calcium supplementation.

Inclusion Criteria:

1. a pathologically confirmed diagnosis of Crohn's disease

2. prior ileal resection with an intact colon (surgery>6 months preceding involvement in study)

3. hyperoxaluria (defined as> 48 mg (>0.5 mmol) per 24 hour urine samples.

   • Patients will not be excluded if they are known kidney stone formers.

Exclusion Criteria:

1. current pregnancy
2. patient's without baseline hyperoxaluria (defined as >48 mg or 0.5mmol per 24 hour urine samples)
3. patients in renal failure assessed by a GFR < 60
4. inability to provide informed consent
5. active cancer
6. hyperparathyroidism
7. hyperphosphatemia
8. <19 years of age