Conditions & Disease States

Conditions & Disease States


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Brief Description: A Vitamin D test is a blood test used to determine if you have a Vitamin D deficiency and to monitor Vitamin D levels if you are on supplementation.

Also Known As: Ergocalciferol Test, Vitamin D2 Test, Cholecalciferol Test, Vitamin D3 Test, Calcidiol Test, 25-hydroxyvitamin D Test, Calcifidiol Test, 25-hydroxy-vitamin D Test, Vitamin D Total Test

Collection Method: Blood Draw

Specimen Type: Serum

Test Preparation: Fasting preferred, but not required.

When is a Vitamin D test ordered?

When calcium levels are inadequate and/or a person exhibits symptoms of vitamin D deficiency, such as rickets in children and bone weakening, softness, or fracture in adults, 25-hydroxyvitamin D is frequently ordered to rule out a vitamin D deficit.

When a person is suspected of having a vitamin D deficiency, the test may be requested. Vitamin D deficiency is more common in older folks, people who are institutionalized or homebound and/or have minimal sun exposure, people who are obese, have had gastric bypass surgery, and/or have fat malabsorption. People with darker skin and breastfed babies are also included in this category.

Before starting osteoporosis medication, 25-hydroxyvitamin D is frequently requested.

What does a Vitamin D blood test check for?

Vitamin D is a group of chemicals that are necessary for the healthy development and growth of teeth and bones. The level of vitamin D in the blood is determined by this test.

Vitamin D is tested in the blood in two forms: 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D. The primary form of vitamin D found in the blood is 25-hydroxyvitamin D, which is a relatively inactive precursor to the active hormone 1,25-dihydroxyvitamin D. 25-hydroxyvitamin D is routinely evaluated to assess and monitor vitamin D status in humans due to its longer half-life and higher concentration.

Endogenous vitamin D is created in the skin when exposed to sunshine, whereas exogenous vitamin D is taken through foods and supplements. Vitamin D2 and vitamin D3 have somewhat different molecular structures. Fortified foods, as well as most vitamin preparations and supplements, include the D2 form. The type of vitamin D3 produced by the body is also used in some supplements. When the liver and kidneys convert vitamin D2 and D3 into the active form, 1,25-dihydroxyvitamin D, they are equally effective.

Some tests may not differentiate between the D2 and D3 forms of vitamin D and just report the total result. Newer methods, on the other hand, may record D2 and D3 levels separately and then sum them up to get a total level.

Vitamin D's major function is to assist balance calcium, phosphorus, and magnesium levels in the blood. Vitamin D is necessary for bone growth and health; without it, bones become fragile, misshapen, and unable to mend themselves properly, leading to disorders such as rickets in children and osteomalacia in adults. Vitamin D has also been proven to influence the growth and differentiation of a variety of other tissues, as well as to aid in immune system regulation. Other illnesses, such as autoimmune and cancer, have been linked to vitamin D's other roles.

According to the Centers for Disease Control and Prevention, two-thirds of the US population has adequate vitamin D, while one-quarter is at risk of inadequate vitamin D and 8% is at risk of insufficiency, as defined by the Institute of Medicine's Dietary Reference Intake.

The elderly or obese, persons who don't receive enough sun exposure, people with darker skin, and people who take certain drugs for lengthy periods of time are all at risk of insufficiency. Adequate sun exposure is usually defined as two intervals of 5-20 minutes each week. Vitamin D can be obtained through dietary sources or supplements by people who do not get enough sun exposure.

This test has 3 Biomarkers

  • Vitamin D Total which is a combined measurement of Vitamin D, 25-Oh, D2 and Vitamin 25-Oh, D3
  • Vitamin D, 25-Oh, D2 which is a measurement of ergocalciferol Vitamin D, which is Vitamin D obtained through plant sources. 
  • Vitamin D, 25-Oh, D3 which is a measurement of cholecalciferol Vitamin D, which is Vitamin D obtained through animal sources.

Lab tests often ordered with a Vitamin D test:

  • Complete Blood Count
  • CMP
  • Iron and TIBC
  • Calcium
  • Phosphorus
  • PTH
  • Magnesium

Conditions where a Vitamin D test is recommended:

  • Kidney Disease
  • Osteoporosis
  • Lymphoma
  • Cystic Fibrosis
  • Autoimmune Disorders
  • Celiac Disease
  • Malabsorption
  • Malnutrition

Commonly Asked Questions:

How does my health care provider use a Vitamin D test?

Determine whether a deficit or excess of vitamin D is causing bone weakening, deformity, or improper calcium metabolism.

Because PTH is required for vitamin D activation, it can aid in diagnosing or monitoring problems with parathyroid gland function.

Because vitamin D is a fat-soluble vitamin that is absorbed from the intestine like a fat, it can help monitor the health of people with conditions that interfere with fat absorption, such as cystic fibrosis and Crohn's disease.

People who have had gastric bypass surgery and may not be able to absorb adequate vitamin D should be closely monitored.

When vitamin D, calcium, phosphorus, and/or magnesium supplementation is suggested, it can help assess the success of the treatment.

What do my Vitamin D results result mean?

Despite the fact that vitamin D techniques differ, most laboratories use the same reference intervals. Because toxicity is uncommon, researchers have focused on the lower limit and what cut-off for total 25-hydroxyvitamin D shortage implies.

A low blood level of 25-hydroxyvitamin D could indicate that a person isn't getting enough sunlight or dietary vitamin D to meet his or her body's needs, or that there's an issue with absorption from the intestines. Seizure medications, notably phenytoin, might occasionally interfere with the liver's generation of 25-hydroxyvitamin D.

Vitamin D insufficiency has been linked to an increased risk of some malignancies, immunological illnesses, and cardiovascular disease.

Excessive supplementation with vitamin pills or other nutritional supplements frequently results in a high level of 25-hydroxyvitamin D.

We advise having your results reviewed by a licensed medical healthcare professional for proper interpretation of your results.