Synonyms

25-OHCC

Clinical Indications

25-hydroxycholecalciferol (25-D), the hepatic precursor to the biologically active 1,25 dihydroxycholecalciferol (1,25-D), is the major circulating metabolite of vitamin D. Measurement of 25-D provides a satisfactory index of vitamin D status for investigation of patients with suspected osteomalcia, rickets or obscure hypo- or hypercalcaemia.

Availability

Analyzed by referral laboratory if specific criteria met.

Specific Criteria

Investigation of suspected vitamin D deficiency or toxicity. Analysis will not  usually be undertaken unless there is other biochemical evidence of vitamin D deficiency (low or low/normal corrected calcium and raised or high/normal PTH). 

Patient Preparation

A fasting sample is preferred but not essential. No further dietary or drug restrictions are required.

Turnaround Time

2 weeks

Specimen

Serum (or plasma for paediatric samples)

Volume

1 ml

Container

Yellow top (SST) tube preferred but for paediatric samples a Paediatric Lithium Heparin (Orange top) may be used.

Collection

Samples should be transported to laboratory as quickly as possible. If delayed protect from light.

Lab. Handling

Separate without delay and store at 4'C. Samples should be posted as soon as possible. Please include calcium, albumin, phosphate, alkaline phosphatase and creatinine levels on referral request form. (VITD & send; NOVD & save)

Causes for Rejection

Not meeting specific criteria for analysis. Delay in sample reaching laboratory. 

Reference Range

Adults: 20 - 110 nmol/L with a seasonal maximum in autumn and a minimum in spring.

Interpretation

Levels below 10 nmol/L are severely deficient whilst 10-20 nmol/L is mild deficiency. Levels between 20-40 nmol/L may be considered sub-optimal, especially when measured in autumn and may not be enough to sustain adequate winter levels. Sustained levels above 200 nmol/L should be viewed with caution and may be consistent with toxicity.