Vitamin D
Other names: 1,25 Dihydroxy-Vitamin D (Calcitriol); 25-Hydroxy-Vitamin D (Calcidiol)
There are two different types of vitamin D which can be measured using a blood test; these are 25-hydroxy-vitamin D and 1,25 dihydroxy-vitamin D. 25-hydroxy-vitamin D is an inactive component, which is converted into the active hormone 1,25-dihydroxy-vitamin D. Vitamin D is taken into the body through the diet and by exposure to sunlight.
Why is the test used?
The test is used to help determine whether a patient has health problems, including vitamin D deficiency, parathyroid hormone problems, problems with bone metabolism and malabsorption.
The test is usually carried out alongside other tests, which may be used to help the doctor reach a more precise diagnosis.
The test is usually ordered when a patient has abnormal electrolyte test results or problems which may result in malabsorption, such as kidney disease. The test may also be used if a patient has a bone disease or problems with their parathyroid hormone.
How is the test done?
The test is done by collecting and analysing a sample of the patient’s blood; blood is usually taken from a vein on the inside of the elbow, using a needle. The blood is drawn out and collected in a syringe before being bottled, labelled with the patient’s name and sent to the laboratory for testing.
What do the test results show?
Low levels of 25-hydroxy-vitamin D may indicate that the individual is not being exposed to enough natural sunlight; low levels may also indicate that the patient is not getting enough vitamin D from their diet. Low levels may also mean that there is a difficulty with the absorption process or a problem which is preventing the conversion of vitamin D into 25-hydroxy-vitamin D.
High levels of 25-hydroxy-vitamin D may indicate that the patient is taking in too much vitamin D; this is usually due to taking supplements.
Low levels of 1,25-dihydroxy-vitamin D may be seen when a patient has kidney disease.
High levels of 1,25-dihydroxy-vitamin D may be caused by excessive production of parathyroid hormone or by conditions, such as lymphoma, which causes the hormone to be produced exterior of the kidneys.
Specific Blood Tests
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Blood Test Guide
- Blood Tests
- Types of blood tests
- what to expect
- What are the risks of blood tests?
- What do blood tests show?
- Specific Blood Tests