Vitamin D

Diagnostic Use

Diagnosis of vitamin D deficiency

Investigation of rickets and osteomalacia

Diagnosis of hypervitaminosis D

Department

Core Biochemistry

Delphic Registration Code

VITD

Synonyms

25-hydroxyvitamin D3
25-hydroxycholecalciferol
Calcidiol
Calciferol
Cholecalciferol
Ergocalciferol

Turnaround Time

2 hours

Test Code

3758

Specimen Type

• Serum

Specimen Requirements

Tube/Container Type:

Preferred

• Serum (Red Cap)
• SST II (Gold Cap)

Preferred Sample Volume (ml)

4.5

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• Serum (Red Cap)

Acceptable

• SST II (Gold Cap)

Preferred Sample Volume (ml)

0.6

Minimum Sample Volume (ml)

0.2

Additional Specimen Information

Effective immediately (as of 14/3/2023), there has been a change to specimen requirements for Vitamin D analysis, with serum now being the only acceptable sample type (Red or Gold top).

We apologise for the inconvenience this will cause, however the change is required due to the manufacturer noting variability of bias between specimen types in the assay, resulting in them withdrawing plasma as an acceptable specimen. They are currently unable to identify the contributing factor and therefore the only option available is to change specimen type. If you require further information, please contact: Duty Biochemist (please call 03 364 0376 and request to be put through)

Aliquot Instructions

Sample Type

• Serum
• Plasma

Transport to Lab

Ambient (8 - 24 degrees Celsius)

Additional Referral/Aliquot Information

Samples may be stored on or off the red blood cells for up to 72 hours. Separated specimens are stable for up to 12 days at 2-8 oC. Outside these timeframes, the separated sample must be stored frozen at -20oC or colder.

Interpretation

This is the preferred test for assessing vitamin D status and most accurately reflects the body’s vitamin D stores.

The main source of vitamin D is the action of sunlight on the skin. Ultraviolet light converts 7-dihydrocholesterol to 25-hydroxyvitamin D3. Vitamin D may also be obtained from the diet from either plant matter as 25-hydroxyvitamin D2 (ergocalciferol or calciferol) or from animal products as 25-hydroxyvitamin D3 (cholecalciferol or calcidiol). Groups at risk of vitamin D deficiency are those with reduced ultraviolet exposure, such as housebound, individuals with darker skin, or wearers of traditional veiled clothing. Vitamin D concentrations are lowest during winter, and low vitamin D tends to recur each winter in susceptible individuals. In such individuals, vitamin D supplementation is reasonable without blood testing.

Most people with low vitamin D are asymptomatic. If prolonged and severe, vitamin D deficiency may lead to rickets in children and osteomalacia in adults; these conditions are uncommon.

The biological half-life of 25-hydroxyvitamin D in plasma is 3 months.
The method used at CHL measures total vitamin D (both D2 or ergocalciferol and D3 or cholecalciferol)

Reference Intervals

25-OH-Vitamin D levels < 25 nmol/L are consistent with moderate to severe vitamin D deficiency.
25-OH-Vitamin D levels 25 – 50 nmol/L are consistent with vitamin D insufficiency.
25-OH-Vitamin D levels > 250 nmol/L are found in vitamin D toxicity.

Optimum range for bone health: 50 – 150 nmol/L

Test Method

Chemiluminescent immunoassay (CLIA) performed on Diasorin Liaison XL analysers using Diasorin reagents.

Method measured total vitamn D (25-hydroxyvitamin D2 and 25-hydroxyvitamin D3)

Non-Funded Test Cost

$29.63 (Exclusive of GST)

Billing Code

3758

Vitamin D analysis by HPLC Tandem mass spectrometry (LC-MS/MS) is still available for research testing by arrangement with the Research study coordinator.

Contact Information

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