Pathology Handbook

1,25 dihydroxy Vitamin D (1,25-DHCC)

Synonyms

1,25 DHCC, 1,25VitD

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).

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Availability

Analyzed by referral laboratory if specific criteria met.

Specific Criteria

1,25-dihydroxyvitamin D is the active metabolite of Vitamin D.  It is formed from 25-hydroxyvitamin D in the proximal tubule of the kidney by the action of 1α hydroxylase.  Levels are tightly controlled and are regulated by PTH, phosphate, calcium and 1, 25-dihydroxyvitamin D itself.  Serum levels give a poor indication of Vitamin D status in deficiency or excess and 25-hydroxyvitamin D should be measured in these situations. 

1,25-dihydroxyvitamin D can also be produced by extra renal synthesis in sarcoidosis, lymphoma and granulomatous disorders.

The primary use of serum levels of 1, 25-dihydroxyvitamin D is in the differential diagnosis of hypercalcaemia, renal disease, secondary hyperparathyroidism, hypocalcaemia and in distinguishing Vitamin D resistance syndromes from Vitamin D deficiency

Patient Preparation

No dietary or drug restrictions are required.

Turnaround Time

4 weeks

Specimen

Serum in red top (plain) tube together with a SST sample for bone profile

Volume

5 ml

Container

Vacutainer red top

Vacutainer gold top

Collection

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

Sent to the Royal Liverpool Hospital.

Causes for Rejection

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

Reference Range

Check the laboratory report.

  • 1,25 di-hydroxy vitamin D:
  • 43-144 pmol/L
  • 25-hydroxy vitamin D:
  • <= 15 nmol/L  : indicative of severe Vitamin D deficiency
  • 16 - 30 nmol/L: indicative of Vitamin D deficiency
  • 31 - 50 nmol/L: indicative of Vitamin D insufficiency
  • > 51 nmol/L     : indicative of adequate Vitamin D status
  • > 150 nmol/L   : may indicate Vitamin D toxicity

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.