Vitamin D Blood Test

At Medical Express Clinic, we offer Vitamin D testing. Checking your vitamin D levels can help in monitoring and diagnosing conditions. Our body uses vitamin D to regulate phosphate and calcium levels. These minerals protect the teeth, muscles, and bones.

Vitamin D is vital to maintain healthy bones and aids efficient glucose metabolism. Most vitamin D in the body is from exposure to sunshine in the warmer months, so vitamin D deficiencies are more common during winter.

Vitamin D is also available in our diet in foods, including red meat, oily fish, eggs, and some fortified foods.

You can contact us to book an appointment with one of our expert team members for your vitamin D test.

What is a vitamin D test?

A vitamin D test measures the vitamin D levels in your blood to ensure you have sufficient levels for your body to function properly. Vitamin D supports healthy teeth and bones and the normal functioning of the immune system, nerves, and muscles.

Low vitamin D level is a common problem that causes bone disorders and other medical issues. Vitamin D testing can inform you if you need to increase your vitamin D levels.

You can get vitamin D in the following three ways.

• Exposure of your bare skin to sunlight for your body to produce vitamin D
• Certain foods, but a few, such as fatty fish and egg yolks, so foods are fortified with vitamin D, including milk, other dairy items, and breakfast cereals
• Vitamin D supplements

Before your body can use vitamin D, the liver must convert it into another form called 25-hydroxyvitamin D (25(OH)D). Most blood tests for vitamin D measure the blood's 25(OH)D levels.

The kidneys use 25(OH)D to produce 'active vitamin D'. Active vitamin D allows your body to use calcium for bone building and helps other cells function properly. If you have abnormal blood calcium levels or kidney problems, your healthcare professional will order a test to check your active vitamin D levels. This is the common test to determine if you have enough vitamin D.

Testing for 25(OH)D is the most accurate way to determine the amount of vitamin D in your blood.

Other names for vitamin D tests are cholecalciferol test, calcidiol test, vitamin D3 test, vitamin D2 test, and 25-hydroxyvitamin D.

Who is the test for?

Vitamin D test lets you know your current vitamin D levels to determine whether you need supplements.

Two types of vitamin D are available – vitamin D2 and D3. Plants make vitamin D2, while the skin makes vitamin D3 from sun exposure. These forms of vitamin D are available in supplements and diets.

Our vitamin D test measures D2 and D3, showing the total of both forms.

People who are likely to have vitamin D deficiency include:

• The older people, especially those house-bound or frail
• People with dark skin (South Asian, African and African-Caribbean ethnicities)
• People who are obese or have undergone gastric bypass surgeries
• Women breastfeeding or pregnant
• Anyone who spends little time outdoors
• People with certain conditions, such as cystic fibrosis (CF), kidney disease or liver disease
• People diagnosed with bone diseases such as osteomalacia, Paget's disease, or osteoporosis
• People with malabsorption conditions such as Crohn's disease or Coeliac's disease

Why perform a vitamin D test?

Vitamin D tests help determine if you have low or excess vitamin D in your blood. Healthcare professionals recommend vitamin D testing for adults, including pregnant women. However, testing may be done for those with a high risk of vitamin D deficiency, such as people who:

• Have thin bones or osteoporosis
• Are obese (or have lost weight following bariatric surgery)
• Are over 65 years (gut absorption of vitamin D and vitamin D skin production reduces as we grow older)
• Are taking certain medicines, like phenytoin
• Have problems absorbing nutrients and vitamins in their intestines, such as people with ulcerative colitis, celiac disease, or Crohn's disease

Normal results

25-hydroxy vitamin D is measured in nanograms per millilitre (ng/mL). Healthcare professionals recommend a level between 20 and 40ng/mL, but 30 to 50ng/mL is acceptable for others.

While these levels are common measurements for vitamin D tests, the normal ranges may differ slightly among different laboratories. You can consult your doctor about the meaning of your test results and if you need vitamin D supplements.

Many people get confused with the reporting of vitamin D tests.

• 25 hydroxy vitamin D3 (cholecalciferol) - This is the vitamin D the body makes or absorbs from animal sources (liver or fatty fish) or a cholecalciferol supplement
• 25 hydroxy vitamin D2 (ergocalciferol) – This is the vitamin D absorbed from foods fortified with plant vitamin D or ergocalciferol supplements
• Both vitamins (ergo and cholecalciferol) work similarly in the body. The total 25 hydroxy vitamin D is the most important value.

What does an abnormal result mean?

A lower-than-normal vitamin D level may be due to vitamin D deficiencies resulting from:

• Dark-pigmented skin, lack of skin exposure to sunlight, or consistently using high-SPF sunscreen
• Poor food absorption
• Liver or kidney disease
• Using certain medications, such as rifampin, phenytoin, and phenobarbital,
• Poor vitamin D absorption resulting from weight loss surgeries, advanced age, or conditions that cause poor fat absorption

Low vitamin D levels are more common in children who are breastfed early and African American children, especially in winter. 

A high vitamin D level may be from excess vitamin D, a condition known as hypervitaminosis D. This condition is mostly due to taking too much vitamin D. It can cause excess calcium in the blood (hypercalcaemia), leading to several symptoms and kidney damage.

Preparing for vitamin D tests?

Vitamin D tests usually require fasting, depending on the lab and testing methods. Ensure you follow the instructions for fasting before your test.

When should I get tested?

Vitamin D testing is useful for diagnosing conditions linked to reduced bone density, depression, osteomalacia, osteoporosis,  or rickets (a condition affecting children).

Your doctor can also recommend a vitamin D test if you take vitamin D supplements and other medications.

What to expect

• Step 1 – preparing for the test

  Ensure you arrive for the test well-hydrated to make the test easier.

• Step 2 – during the test

  A vitamin D test is a simple blood test. Our healthcare professional will insert a needle into a vein in your inner arm to draw a small amount of blood. This may cause a slight scratching or pricking sensation.

• Step 3 – results

  We will email your results once they are available from the lab. Our GP will also contact you directly if you had a consultation with us.

If you only booked for the test, you can take the result to your doctor, but you can also book a consultation with us afterward if you need our doctor to evaluate your result.

GMC-registered GPs provide our consultations, and a fee applies for this service.