What is a vitamin D blood test?

Vitamin D is important for healthy bones.

Vitamin D comes in two forms:

1. vitamin D2 (ergocalciferol)
2. vitamin D3 (cholecalciferol)

Vitamin D2 and vitamin D3 need to be turned into 25-hydroxy-vitamin D to work effectively. This is done by your liver and kidneys.

The vitamin D blood test measures how much 25-hydroxy-vitamin D is available in your body.

Other forms of vitamin D can also be measured if needed.

Why would I need this test?

A vitamin D test might be part of a check-up for certain people who may not have enough vitamin D. You could have low vitamin D levels (deficiency) if you are:

• older
• frail
• don’t get outside in the sunshine very much

Your doctor might also recommend this test if you have:

• abnormal levels of minerals such as calcium, phosphate or magnesium in your blood
• problems or weakness in your bones (such as osteoporosis)
• a health condition that might result in, or be caused by, too much or too little vitamin D for example
• cystic fibrosis
• Crohn’s disease
• kidney disease
• problems with your parathyroid gland
• low sun exposure

How do I need to prepare for this test?

No special preparation is required for a vitamin D blood test.

Understanding your results

A low level of 25-hydroxy-vitamin D may mean:

• you are not getting enough vitamin D from sunlight or from food
• you have problems with vitamin D absorption from your intestines
• your liver is not making enough of this type of vitamin D

A high level of vitamin D could mean:

• you are taking too much of a vitamin D supplement
• you have a parathyroid problem or other medical condition

Vitamin D levels can be higher in summer than in winter.

Talk to your doctor about what your results mean for you.

Resources and support

About Vitamin D testing

Go to the Pathology Tests Explained website for more information about Vitamin D testing.

Read the Royal Australian College of General Practitioners’ (RACGP) patient fact sheet on Vitamin D testing.

About bone health

Visit Healthy Bones Australia to learn about bone health and osteoporosis.

About blood testing

See healthdirect’s 'Guide to blood testing' to learn more about blood tests in general including information such as:

• what happens during a blood test
• the accuracy of your results
• the cost of your blood tests