Contributed by – Healthians Team
What is the Vitamin D 1,25 Dihydroxy test?
There are two forms of vitamin D in the blood – 25-hydroxy and 1,25-dihydroxy. In the vitamin D 1,25 dihydroxy test, the levels of the latter form are tested.
1,25 dihydroxy is the active form of vitamin D produced in the liver and kidneys through the conversion of vitamin D 25-hydroxy. It is to be noted that this particular form of vitamin D has no relationship with vitamin D stores. Parathyroid hormone regulates vitamin D 1,25-dihydroxy. And if there’s a deficiency of vitamin D in the body, the levels of this form go up which would give false results in case used to diagnose the deficiency. Instead, the vitamin D 25-hydroxy test should be used for that purpose.
Who should get tested?
Typically, it is ordered when symptoms of kidney disease are present or abnormalities of the enzyme that convert vitamin D 25-hydroxy to vitamin D 1,25-dihydroxy are suspected. The test may also be done when calcium levels are high or diseases that produce excess amounts of vitamin D are present.
Why is the test needed?
Your doctor may ask for Vitamin D 1,25 hydroxy test to:
- make a differential diagnosis of hypocalcemia
- monitor patients with renal osteodystrophy or chronic renal failure
- check for abnormality associated with the enzyme that converts vitamin D 25-hydroxy to vitamin D 1,25-dihydroxy
- diagnose kidney-related issues, hyperparathyroidism, pseudohypoparathyroidism, renal osteodystrophy, or vitamin D-resistant rickets
What does Vitamin D 1,25-Dihydroxy test result mean?
Generally, 19.6 to 54.3 pg/ml is considered a normal range of vitamin D 1,25-dihydroxy. However, each lab may have slightly different reference ranges. So, the test results from different labs may also vary.
Having low levels of vitamin D 1,25-dihydroxy in the blood could indicate the presence of kidney diseases. It is also one of the earliest changes that happen in case of early kidney failure.
Whereas, having high levels of vitamin D 1,25-dihydroxy in the blood could mean that there is excess parathyroid hormone or diseases such as sarcoidosis or lymphomas are present.
How is the test done?
For the vitamin D 1,25-dihydroxy test, a small amount of your blood is needed. It is usually drawn from a vein in the arm. The process is quick and always done by a professional. It’s usually painless. At the most, you may feel a small prick at the site where the needle is inserted. Although, fasting is not needed before the blood sample collection, make sure that you inform your doctor about any existing medical conditions and the medication you might be on as they can influence your test results.
