25-Hydroxyvitamin D

Clinical Use
1 Investigation of disorders of mineral metabolism in children.

2 Diagnosis of vitamin D deficiency in adults.

3 Investigation of suspected vitamin D intoxication.

25-Hydroxyvitamin D (25-hydroxycalciferol), the immediate precursor of the biologically active renal metabolite 1,25-dihydroxycalciferol, is the major circulating metabolite of vitamin D. Measurement provides a satisfactory index of vitamin D status for the investigation of patients with suspected osteomalacia, rickets or obscure hyper- or hypocalcaemia.

Patient Preparation
None. No special dietary restriction is necessary. Take blood (5 mL) into a syringe or red-topped vacutainer.

Sample Preparation
Transfer the blood to a plain glass tube and allow to clot for 30 min. If using a vacutainer, allow blood to clot in vacutainer. *Freeze the serum (-20C) promptly. Send serum (2 mL) to the SAS laboratory. Ensure the sample remains frozen during transport.

*Frozen samples are not required by Manchester or Newcastle.

Reference Range
There is some seasonal variation. Normal ranges are provided with results.

Centres offering this assay
Cardiff UHW Hormone and Steroid Laboratory
London Imperial Charing Cross Hospital Endocrine Laboratory
Manchester Royal Infirmary Vitamin D Service
Newcastle Royal Infirmary Endocrine Laboratory

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