Referred to external laboratory.
When assessment of Vitamin D stores is indicated, 25 OH Vitamin D should be measured. 1, 25 OH Vitamin D does not reflect tissue stores, serum levels are largely determined by PTH and renal 1-alpha hydroxylase activity. 1, 25 OH Vitamin D testing is performed in Australia.
Choosing Clinical Laboratory Tests Wisely Guidelines:
- Do not perform population based screening for Vitamin D deficiency.
- Avoid ordering Vitamin D concentrations routinely in otherwise healthy children, including children who are overweight or obese.
- Vitamin D tests were developed for investigation of rickets, osteomalacia and other metabolic bone disorders. In recent years the number of requests for tests has increased dramatically.
- Most of these requests are unrelated to metabolic bone disease, and have arisen because of reported associations between various disorders (cancers, cardiovascular disease, diabetes, autoimmune disorders and infectious diseases) and lower vitamin D concentrations. However, a causal link with vitamin D has yet to be demonstrated. A recent comprehensive literature review has concluded that there is little evidence for testing vitamin D in patients without symptoms of metabolic bone disease.
- It is not necessary to routinely measure vitamin D in patients with low bone density. It is reasonable to routinely provide vitamin D supplements without testing vitamin D to frail housebound or institutionalized elderly people, or those in the community who practice sunlight avoidance for cultural or medical reasons.
Testing is indicated in the following circumstances:
- Specific high risk groups for rickets/osteomalacia (cystic fibrosis, proven malabsorption),
- When ordered for the investigation of rickets/osteomalacia, osteoporosis/osteopenia, disorders of calcium and phosphate metabolism, elevated ALP, hepatitis C,
- Patients on anticonvulsants.
- Do not test for 25-hydroxyvitamin D unless these indications are present.
- Do not repeat tests for 25-hydroxyvitamin D to monitor the response to Vitamin D therapy. Exceptions include patients on long term parenteral nutrition, weight loss surgery or significant malabsorption syndromes.