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PTD - 317

Test Directory -  1,25 dihydroxycholecalciferol (vitamin D)

Synonyms

1,25 DHCC

Clinical Indications

1,25-dihydroxycholecalciferol (1,25-D), the active metabolite of vitamin D is formed in the kidney from 25-hydroxycholecalciferol (25-D). 1,25-D may also be produced by other cells in some pathological conditions (sarcoidsosis, tumours).

Availability

Referred test: Analysed by Clinical Biochemistry, Epsom Hospital, Surrey, if specific criteria met.

Specific Criteria

Investigation of inherited rickets/vitamin D dependent rickets. 1-25-D may also be useful to confirm hypercalcaemia due to sacrcoidosis and in the investigation of oncogenic osteomalcia.

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

2 ml

Container

Yellow top (SST) tube or

Paediatric orange top (lithium-heparin)

Please contact laboratory before collection. Samples should be transported to laboratory immediately.

Causes for Rejection

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

Reference Range

Adults: 40 - 150 pmol/L. Levels may be up to 20% higher in children due to the effects of growth hormone.

Interpretation

In type 1 (deficient 1 alpha-hydroxylase) inherited rickets 1,25-D is low and in type 2 (end-organ resistance) 1,25-D may be high. 1,25-D may also be elevated in hereditary hypophosphataemic rickets with hypercalcuria. 25-D is usually normal in all three.

Lab. Handling

Processing: Separate into 2 aliquots immediately (within 1 hour of collection) and freeze at -20C in separating freezer (CB40), active frozen rack 110. Referral: Send sample to the referral laboratory frozen. Please include calcium, albumin, phosphate, alkaline phosphatase and creatinine levels on referral request form.
(VD125 & send; NOVD & save)


Version 1.0 / October 2014                                                                                                     Approved by: Consultant Biochemist