1,25-dihydroxyvitamin D (Calcitriol)
This test measures 1,25-dihydroxyvitamin D, the biologically active form of vitamin D. It is used to investigate calcium imbalance, kidney disease and complex vitamin D disorders.
Turnaround time
Results available 5-8 days after arrival in lab. Doctor's report sent the day after results available (if required)
Biomarkers count
1
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Details about 1,25-dihydroxyvitamin D (Calcitriol)
What is the 1,25-Dihydroxyvitamin D (Calcitriol) Test?
The 1,25-dihydroxyvitamin D test measures calcitriol, the hormonally active form of vitamin D responsible for regulating calcium and phosphate balance in the body. Unlike the more commonly tested 25-hydroxyvitamin D, calcitriol reflects vitamin D activation rather than overall vitamin D stores.
Calcitriol is produced through a two-step process: vitamin D is first converted in the liver, then activated in the kidneys. This active form directly influences calcium absorption from the gut, bone metabolism and parathyroid hormone (PTH) activity.
Because calcitriol levels are tightly regulated, this test is used in specific clinical situations rather than routine vitamin D screening.
Why do I need a test for 1,25-Dihydroxyvitamin D?
You may need this test if there are abnormalities in calcium, phosphate or parathyroid hormone levels that cannot be explained by standard vitamin D testing. Calcitriol measurement is particularly important when kidney function is impaired, as the kidneys play a key role in vitamin D activation.
This test is also used when certain inflammatory or granulomatous diseases are suspected, as these conditions can cause excessive conversion of vitamin D to its active form, leading to high calcium levels.
Symptoms and scenarios where testing is recommended:
- Unexplained high or low calcium levels
- Chronic kidney disease
- Abnormal parathyroid hormone (PTH) results
- Suspected vitamin D metabolism disorders
- Sarcoidosis or other granulomatous disease
- Unexplained bone pain or fractures
- Disorders of phosphate balance
- Investigation of calcium-related kidney stones
Benefits of the 1,25-Dihydroxyvitamin D Test
- Assesses active vitamin D function
Measures the hormone responsible for calcium and phosphate regulation. - Clarifies complex calcium disorders
Helps explain unexplained hypercalcaemia or hypocalcaemia. - Essential in kidney disease assessment
Identifies impaired vitamin D activation in renal dysfunction. - Supports parathyroid disorder diagnosis
Interpreted alongside PTH to assess calcium-hormone balance. - Identifies abnormal vitamin D activation
Useful in granulomatous and inflammatory diseases. - Prevents misinterpretation of vitamin D status
Differentiates storage deficiency from activation problems. - Guides specialist endocrine or renal care
Results influence further investigation and treatment. - Targeted, clinically specific testing
Used when standard vitamin D tests are insufficient.
Step-by-Step: How Testing Works
Choose your preferred testing method
You can attend one of our UK partner clinics or arrange a home or hotel visit with a mobile phlebotomist.
Option 1 – In-Clinic Blood Draw
- Select your nearest UK clinic and book an appointment.
- A clinician or phlebotomist collects a venous blood sample.
- The sample is analysed for calcitriol levels.
- Results are delivered securely online.
Option 2 – Home or Hotel Phlebotomy (+£60)
- Book a UK-wide home or hotel visit at a convenient time.
- A trained phlebotomist collects your blood sample on-site.
- The sample is packaged and transported to the laboratory.
- Results are uploaded digitally without the need to travel.
Access your report
You can download and share your results with your GP, endocrinologist or renal specialist.
Your Results Explained
Low Levels
Low calcitriol levels suggest reduced vitamin D activation, most commonly due to kidney disease or severe vitamin D deficiency.
This can lead to poor calcium absorption and bone mineral loss.
Typical UK reference range: approximately 48–190 pmol/L (ranges vary by laboratory).
Normal Levels
Normal results indicate appropriate vitamin D activation and balanced calcium regulation.
This suggests the kidneys and parathyroid system are functioning as expected.
High Levels
Elevated calcitriol levels indicate excessive vitamin D activation.
This may occur in granulomatous diseases, certain lymphomas or rare metabolic disorders and is often associated with high calcium levels.
Further investigation is usually required to identify the underlying cause.
How It Works
Simple steps to get your results
Book Online
Choose your test online and book in seconds. Select your preferred clinic location or home visit option.
Visit or Test at Home
Attend one of our UK or London clinics, arrange a home nurse visit, or use a finger-prick kit where available.
Get Your Results
Your sample is analysed by accredited UK laboratories, with secure results delivered directly to you.
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WhatsApp UsHow to Prepare for Your Test
Follow these guidelines for accurate results
Sample Timing
Where possible, attend your blood test between 7am and 12pm. Please wait until any short-term illness or infection has fully resolved before testing. Avoid intense exercise for 24–48 hours beforehand, as this can affect certain markers.
Fasting & Hydration
Fasting is not always required, but some tests may recommend it. If fasting is advised, avoid food for 8–12 hours before your appointment and drink water only. Stay well hydrated, as this helps with sample collection and accuracy.
Medications & Supplements
Continue prescribed medications unless advised otherwise by your clinician. Avoid vitamin, mineral, or biotin supplements for at least 24–48 hours before your test, as these can interfere with results. If you are unsure about any medication or supplement, please let us know before your appointment.
Hormones & Menstrual Cycle
For hormone-related tests, timing within your menstrual cycle may be important. If relevant, follow any specific guidance provided on your test page.
If you have any questions or special circumstances, our team is happy to advise before your appointment.