Vitamin D test

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.