Some quick facts about vitamin D

1,000 unit capsules/gel tabs of vitamin D3 cost 3 to 5 cents each.
The assay cost (not the charge) for measurement of 25 hydroxyvitamin D (25OHD) is $10 to $16.
Up to 10,000 units of vitamin D daily is not a toxic dose.
There is little need to measure 25OHD on a routine basis.
The normal range for 25OHD in African-Americans is lower than in non-Hispanic whites, yet their bone density is greater. There is even less need to measure 25OHD in African-Americans.
The vitamin D content of milk is not well regulated. Milk is a good source of calcium but might not be a good source of vitamin D.
Many multi-vitamins contain 400 units of vitamin D and 10,000 of vitamin A. In order to get the recommended 1,000 to 1,500 units of vitamin D you need three multi-vitamin tablets. This provides 30,000 units of vitamin A — a dose that is toxic to the skeleton. Multi-vitamins are not the ideal way for your patient to get the recommended daily dose of vitamin D.

When then should you think about measuring 25OHD?

Vitamin D deficiency often leads to a proximal myopathy. Ask your patient to fold her/his arms and stand up from a sitting position without using their arms. If they cannot do this think seriously about vitamin D deficiency, and of course other potential causes of proximal myopathy.
Patients with chronic GI conditions associated with malnutrition (e.g. Crohn’s, ulcerative colitis, s/p bariatric surgery) are candidates for vitamin D deficiency.
Patients with eating disorders may be deficient in many nutrients.
In patients in whom the standard biochemical profile has a low serum phosphate or an elevated serum alkaline phosphatase with normal aspartate aminotransferase (AST) and alanine aminotransferase (ALT), don’t wait to think of vitamin D deficiency until the serum calcium is low!! That is a very late manifestation because the vitamin D-PTH axis works hard to keep serum calcium normal.