Vitamin D is required for absorption of calcium and phosphate from the gut. The majority of vitamin D is produced in the skin when exposed to sunlight and the remainder obtained in the diet.
25-hydroxy vitamin D (25OHD) is the most abundant vitamin D metabolite in the circulation. It is relatively inactive but its measurement is the best indicator of vitamin D status. 25OHD exists in two forms, D3 and D2, and both are equally measured by the LC/TMS method.
Assessment of vitamin D status is important in patients with abnormal calcium or phosphate levels, possible osteomalacia and malabsorption, and osteoporotic patients before giving the first dose of IV bisphosphonates (to reduce the risk of drug induced hypocalcaemia).
NB. Request intervention procedures have been set up to reduce unnecessary testing. The request intervention interval for vitamin D is 340 days. All repeat requests within this period are reviewed by the Duty Biochemist and may be over-ridden if appropriate clinical details are provided.
Vitamin D Requesting and Prescribing Guidelines
Click here to access the NHSGGC Vitamin D Guidelines
Sample Requirements and Target Values
|Minimum volume||2 mL|
<25 nmol/L: Vitamin D deficient, consider supplementation
25 - 49 nmol/L: Borderline low vitamin D, risk of secondary hyperparathyroidism, consider increase in vitamin D intake
>50 nmol/L: Adequate vitamin D
|Turnaround time||14 days|
|Method||Liquid chromatography-tandem mass spectrometry|