Vitamin D 1,25 - Dihydroxy Test

The vitamin D 1,25 – dihydroxy test checks the amount of 1,25 – dihydroxy vitamin D (the active form of vitamin D) in a blood sample. It is also known as the calcitriol test.

1,25 – dihydroxy vitamin D helps your body absorb calcium to build healthy bones and teeth. It also helps muscles, nerves, and the immune system work properly. Unusual levels of calcium in the body can cause rickets (soft and weak bones in children), osteomalacia (soft and weak bones in adults), osteopenia (low bone density), and osteoporosis (weak and brittle bones that break easily).

The routine vitamin D test checks how much vitamin D is stored in your body, while the 1,25 – dihydroxy vitamin D test measures the active form that your body uses. Doctors use this test to investigate the underlying causes of calcium imbalance-related problems and to guide treatment.

The test may be recommended for the following categories of people:

• Individuals with abnormal calcium levels – The test can be used to find out the cause of abnormal calcium levels in the body.
• Individuals with suspected parathyroid gland disorders – This test helps investigate conditions such as hyperparathyroidism and hypoparathyroidism.
• Individuals with bone disorders – To help investigate conditions such as rickets and osteomalacia when the underlying cause is not clear.
• Individuals with kidney disease – To assess whether the kidneys are producing enough of the active form of vitamin D.
• Individuals with suspected Vit D metabolism issues – Certain conditions such as sarcoidosis can affect the production of active vitamin D.

The vitamin D 1,25 test can be used with other tests to help detect certain conditions, such as:

• Sarcoidosis – This is a condition in which small clumps of immune cells form in different parts of your body, causing inflammation.
• Chronic kidney disease (CKD) – Damaged kidneys may not produce enough of the active form of vitamin D.
• Osteomalacia – This is a condition characterised by the softening of bones. It is called rickets in children.
• Hypercalciuria – This refers to the presence of excess calcium in the urine.
• Hypercalcaemia – This refers to excess calcium in the blood.
• Parathyroid gland disorders – This test may help investigate certain disorders of the parathyroid gland.

What to Expect Before the Vitamin D 1,25-Dihydroxy Test

No fasting is required for a standalone Vitamin D 1,25-Dihydroxy test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise Vitamin D 1,25-Dihydroxy levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Vitamin D 1,25-Dihydroxy Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

In the vitamin D 1,25 test, the primary parameter being measured is:

• The levels of 1,25 – dihydroxy vitamin D in a sample of blood

The vitamin D 1,25 test normal range is shown in the table below.

The interpretation of the vitamin D 1,25 test is given in the table below.

Like other medical tests, this test also has certain risks and limitations.

Risks:

The test is usually safe and involves minimal risk. You may feel slight pain when the needle is inserted or mild bruising afterwards, which usually resolves spontaneously.

Limitations:

• Medicines, vitamins, and supplements may affect your test results. Be sure to ask your doctor for the correct advice if you need to temporarily stop taking them.
• Abnormal results do not always mean you have a health problem. Your doctor will consider your symptoms, medical history, and other test results before making a diagnosis.

Depending on your symptoms and results, your doctor might recommend the following tests to better understand your condition:

• Calcium blood test
• Creatinine test
• Phosphate test
• Parathyroid hormone test
• Bone density scan
• 25-hydroxy vitamin D test