Suitable Specimen Types


Vitamin D (25-OH VitD)

Specimen Volume

5mL blood (0.25mL serum)

Turnaround Time

7 Days

Sample Stability

<36 days at 4°C>

General Information

Vitamin D is the generic name for a group of closely related steroids. Vitamin D is a hormone rather than a vitamin. The majority of Vitamin D is produced by the action of UV light on 7 dehydrocholesterol in the skin to produce Vitamin D3 - cholecalciferol. A minor proportion comes from food as Vitamin D2-ergocalciferol.


Vitamin D itself is biologically inert. It is metabolised to 25-OH Vitamin D in the liver and thence to the active form 1,25-OH Vitamin D by 1a hydroxylase in the kidneys. In the circulation most of the Vitamin D is bound to Vitamin D binding protein and a smaller amount to albumin.


Vitamin D plays a major role in calcium homeostasis. It increases calcium absorption from the gut, promotes bone mineralisation by provision of calcium, reduces 1a hydroxylase activity in the kidneys and reduces PTH production by the parathyroid glands.


It has other functions that are not as well understood. These include regulation of cellular differentiation and immunomodulation. Measurement of 25-OH-Vitamin D3 assesses the principal storage form of the vitamin.


Causes of low Vitamin D

Reduced production - lack of sunlight

Reduced intake - lack of intake in diet

Reduced absorption - biliary disease

Catabolism - anticonvulsant therapy

Reduced metabolism - chronic renal failure

Inherited diseases


Causes of high Vitamin D

Increased ingestion - diet / iatrogenic

Increased production - granulomatous disease / lymphoma



Patient Preparation



Vitamin D is assayed by tandem mass spectrometry

Reference Range

<30 nmol/L - Vitamin D deficiency,

30-50 nmol/L - Borderline low vitamin D

>50 nmol/L - Adequate vitamin D

>300 nmol/L - may indicate Vitamin Toxicity


  • EQA Status: NEQAS
  • EQAS Scheme: Yes

General Information

General information about the website and its content

Location of Laboratories

Where the laboratories are located and information about the services offered at each laboratory