At a Glance

Vitamin D deficiency with rickets is caused by insufficient cholecalciferol (prohormone) synthesis in the skin due to sun-dependent synthesis to support cartilage mineralization. This causes wide growth plates and secondary bowing of long bones, as well as a number of secondary metabolic problems, including poor calcium uptake.

Vitamin D deficiency with rickets has largely been eliminated by supplementation of food, particularly dairy products with vitamin D.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

If vitamin D deficiency is possible because of physical findings, a vitamin D level (25 hydroxyvitamin D) is diagnostic. 25 hydroxyvitamin D levels are very low, < 10 ng/mL. Normal serum phosphate should be verified, and, with primary rickets, generally, serum calcium is low or low normal.

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Note, however, that primary vitamin D deficiency is so rare that the possibility of an inherited defect should strongly be considered in any apparent case of primary rickets in a child in the developed world.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?

Secondary causes of vitamin D deficiency, including anticonvulsants and occasionally other drugs, should be considered. It is important to consider these secondary causes and unrelated causes, such as renal phosphate wasting, at the same time vitamin D is assayed, because these are much more common than primary vitamin D deficiency.

What Lab Results Are Absolutely Confirmatory?

Correction with vitamin D treatment is definitive.