Vitamin D Test (Vitamin D2, D3 and D Total)

Test ID: B-223 | Sample Type: Dried Blood Spot | Test Method: LC-MS/MS | Results: 3–5 Working Days | Laboratory: ZRT Laboratory – CLIA Certified | Report: Specialist Doctor Comment Included | Suitable For: Adults and Children | Collect Sample At Home: No Clinic Visit Required

Could Vitamin D Deficiency Be Behind Your Fatigue, Pain, or Low Mood?

Vitamin D deficiency is one of the most widespread and underdiagnosed nutritional issues in the UK — affecting an estimated 1 in 5 adults. It often has no obvious symptoms, yet it silently increases the risk of serious health conditions. If you recognise any of the following, a Vitamin D test could be the missing piece:

• Persistent fatigue or low energy that doesn’t improve with rest
• Bone pain, aching joints, or muscle weakness
• Frequent illness or infections (low immunity)
• Low mood, depression, or seasonal mood changes
• Hair loss or slow hair growth
• Chronic back pain or musculoskeletal discomfort
• Spending most of your time indoors or living in the UK or northern latitudes
• Dark skin tone (requires more sun exposure to produce Vitamin D)
• Overweight or obese (Vitamin D can become trapped in fat tissue)
• Taking Vitamin D supplements and unsure if your levels are optimal
• Elderly or at risk of osteoporosis or fractures

What Is Vitamin D and Why Does It Matter?

Vitamin D is a prohormone — not just a vitamin — that plays a critical role in dozens of body systems. Most of it is produced by the skin in response to sunlight, with very little coming from diet alone. In the UK, low sunlight levels make deficiency extremely common, particularly in autumn and winter.

Research links Vitamin D deficiency to a wide range of serious conditions, including osteoporosis and increased fracture risk, cardiovascular disease and stroke, type 1 and type 2 diabetes, autoimmune conditions including multiple sclerosis and rheumatoid arthritis, depression and mood disorders, and chronic musculoskeletal pain.

What This Test Measures

This is one of the most precise Vitamin D tests available, using LC-MS/MS technology to independently measure both forms:

• Vitamin D2 (Ergocalciferol) — the form found in plant-based foods and many supplements
• Vitamin D3 (Cholecalciferol) — the form produced by sunlight and found in animal-based foods
• Total Vitamin D (25-OH) — the calculated combined level used to assess overall Vitamin D status

Measuring D2 and D3 separately is important for anyone supplementing, as it shows exactly which form is contributing to your levels and whether your supplementation is working.

25-OH Vitamin D Ranges

Unit: ng/mL

*Applicable unless supplementing with vitamin D2.

Who Should Consider This Test?

• Persistent fatigue, bone pain, muscle weakness, or low mood
• Frequent illness or low immunity
• Living in the UK or spending limited time outdoors
• Dark skin tone or overweight (both reduce Vitamin D synthesis)
• Currently taking Vitamin D supplements and wanting to confirm optimal dosing
• Elderly or at risk of osteoporosis
• Anyone wanting a precise D2 vs D3 breakdown rather than a total-only result

How It Works

1. Order your kit — delivered to your door
2. Collect your sample at home — a simple finger-prick dried blood spot; no clinic or GP visit needed
3. Post your sample to ZRT Laboratory using the return instructions provided
4. Receive your results by email within 3–5 working days of the lab receiving your sample

What You Receive

• Your D2, D3, and Total Vitamin D levels displayed clearly in graphics and numbers
• Written interpretation by a Hormone Specialist PhD Doctor
• Guidance on whether your levels are deficient, low, or optimal, and what to do next
• Laboratory fee included — no hidden charges

Why We Use ZRT Laboratory

All testing is performed by ZRT Laboratory — a globally recognised, CLIA-certified diagnostic laboratory founded in 1998 by Dr. David Zava, PhD. ZRT has performed over 11 million tests and is trusted by healthcare professionals in 96+ countries. ZRT’s LC-MS/MS Vitamin D test independently measures D2 and D3 — a level of precision not available from standard immunoassay-based Vitamin D tests.

Frequently Asked Questions

Why does this test measure D2 and D3 separately?
Most standard Vitamin D tests only report a total 25-OH value. Measuring D2 and D3 separately shows which form is driving your total level — essential if you are supplementing, as D2 and D3 supplements have different potency and conversion rates.

What is the optimal Vitamin D level?
Optimal levels are generally considered to be 32–100 ng/mL. Levels below 20 ng/mL indicate deficiency; levels below 32 ng/mL are considered low. Your specialist report will interpret your result in context and advise on supplementation if appropriate.

Does the price include the laboratory fee?
Yes. The full laboratory analysis fee is included. You are only responsible for posting your sample to the laboratory.

How long is the kit valid for?
The kit must be used within 12 months of the purchase date.