A challenging case of hypocalcemia supporting the concept that 25-hydroxyvitamin D status is important for intestinal calcium absorption.

Context: Intestinal mucosa seems to be responsive not only to circulating calcitriol but also to serum 25-hydroxyvitamin D concentrations.

Objective: We report a complex patient with chronic kidney disease who presented with symptomatic hypocalcemia (ionized calcium, 0.77 mmol/liter) despite regular calcitriol and calcium supplementation.

Methods: Case history, laboratory evaluation, and bone biopsies are discussed.

Results: Only vigorous treatment with im cholecalciferol led to a significant improvement of serum calcium, a decrease in PTH levels, and histological improvement of osteomalacic bone disease. However, oral anticoagulation became necessary for advanced peripheral artery disease, which precluded further im injections. Therefore, UVB phototherapy was initiated to treat vitamin D deficiency.

Conclusion: This case is clinically relevant because it demonstrates that efficient calcium absorption is markedly reduced in profound vitamin D deficiency, even with normal active vitamin D levels. An important consequence is to stay aware of vitamin D deficiency in patients with compromised kidney function irrespective of regular calcitriol replacement. Second, when both parenteral and oral vitamin D administration are contraindicated, ineffective, or unavailable, UVB phototherapy is an effective option to treat vitamin D deficiency. Third, this case underlines the importance of obtaining regular 25-hydroxyvitamin D levels in complex clinical cases when prediction of individual response is unreliable.