25-Hydroxyvitamin D with 1,25-Dihydroxyvitamin D

Clinical Use
Investigation of disorders of mineral metabolism.

Application
1,25-Dihydroxyvitamin D, the active metabolite of vitamin D is formed in the kidney and in some pathological conditions, also in other cells. Measurement may be useful in renal disease, in primary and secondary hyperparathyroidism and hypoparathyroidism and in distinguishing the various types of vitamin D resistant states from vitamin D deficiency. Assays may also assist in investigation of malignancy-associated hypercalcaemia and sarcoidosis.

25-Hydroxyvitamin D will also be measured on the same sample, since results for 1,25-dihydroxyvitamin D cannot be interpreted without this information. The assays measure both the D3 and D2 forms of the vitamin

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.

Reference Ranges
25-Hydroxyvitamin D: 5-30 ng/mL; (12.5-75 nmol/L)

1,25-Dihydroxyvitamin D: 20-50 pg/mL; (48-120 pmol/L)

Centre offering this assay
Manchester Royal Infirmary Vitamin D Service

References
Mawer EB, Berry JL, Cundall JP, Still PE and White A . A sensitive radioimmunoassay that is equipotent for ercalcitriol and calcitriol (1,25-dihydroxyvitamin D2 and D3). Clin Chim Acta 1990; 190: 199-210.

Mawer EB and Berry JL (1995). The biochemistry of calcium regulation. Chapter 5, pp 49-75 in The Measurement of Metabolic Bone Disease. Ed FI Tovey and T Stamp, Parthenon Publishing, Carnforth, Lancs, in press.

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