Vitamin D testing explained

The most accurate way to find out how much vitamin D is in your body is through a simple blood test. A small sample of blood is taken, usually from a vein in the arm, to measure the amount of 25‐hydroxyvitamin D (25‐OHD). This is the major circulating form of vitamin D in the body and can help determine whether your body’s vitamin D level is adequate or deficient.

What will a vitamin D test tell me?

A vitamin D blood test helps your doctor establish your vitamin D status. As a general guide:1

  • If your vitamin D (25‐OHD) levels are ≥ 50 nmol/L, then you’re likely to have adequate vitamin D. Your levels should be slightly higher in summer to allow for decreases in the colder months.
  • If your vitamin D (25‐OHD) levels are 30‐49 nmol/L, then you’re considered to have a mild vitamin D deficiency and your doctor may advise sensible sun exposure and/or a vitamin D supplement.
  • If your vitamin D (25‐OHD) levels are 12.5 nmol/L‐29 nmol/L then you’re likely to have a moderate vitamin D deficiency and your doctor may advise a vitamin D supplement to increase your body levels of vitamin D.
  • If your vitamin D (25‐OHD) levels are <12.5 nmol/L then you’re likely to be very vitamin D deficient and your doctor will advise suitable treatment.

Vitamin D deficiency can be detrimental to your bone, muscle and overall health, so it’s important to maintain adequate levels.

Do I need a vitamin D test?

Those who are at a high risk of developing vitamin D deficiency may be advised to get a blood test to determine their vitamin D status. This includes:

  • People who are housebound, particularly those who are 65 years and older or in aged care facilities2.
  • People with naturally darker skin tones2.
  • Those who wear modest clothing for cultural or religious reasons1.
  • Those who avoid the sun for health or other reasons1.
  • Very overweight people1.
  • People who have a health condition or take medicines that may affect the absorption of vitamin D2.
  • Pregnant women with any of the above risk factors2.

Are there any side effects?

Vitamin D testing is conducted via a simple blood test, therefore reactions are rare. Some people may experience short‐term discomfort but it’s usually a quick and easy procedure.