Vitamin D Deficiency

Vitamin D Deficiency Testing and health information

You can order a blood test to measure your levels of vitamin D directly with Ulta Lab Tests. The Vitamin D, 25-Hydroxy, Total and the Vitamin D, 25-Hydroxyvitamin D (D2, D3), LC/MS/MS (QuestAssureD™) are the most common test, followed by the Vitamin D, 1,25-Dihydroxy, LC/MS/MS test.


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Vitamin D Testing comes in two forms when found in the bloodstream: 1,25-dihydroxyvitamin D and 25-hydroxyvitamin D. Specialists concentrate on 25-hydroxyvitamin D when testing a person’s vitamin D levels because of it’s higher concentration and longer half-life. It is responsible for the development of healthy teeth and bones.

The human body can be exposed to vitamin D in two distinct manners – endogenous and exogenous.

Endogenous sources refer to general exposure to vitamin D, such as standing in the sunlight. In contrast, exogenous sources are ingested, such as food and supplements. The sources can vary when it comes to their chemical structures, which is why they are given different names. For example, vitamin D2 (ergocalciferol) is used to highlight plant-based types.

In contrast, vitamin D3 (cholecalciferol) is used to describe animal-based types. With vitamin D2, it is generally ingested through fortified foods, supplements, and/or vitamin preparations. On the other hand, vitamin D3 can be produced by the human body and/or ingested through supplements. When it comes to general efficiency, both vitamin D2 and D3 are efficient. They can easily be converted into 1,25-dihydroxyvitamin D by the liver.

The average test will not break down specific types of vitamin D. It will often refer to them as a singular unit. However, new-age testing methods are starting to incorporate intricate processes to help differentiate between D2 and D3 in the blood.

Vitamin D is responsible for regulating the amount of phosphorus, magnesium, and calcium found in the blood. Therefore, vitamin D is noted for its natural impact on the growth and formation of bones. If the body does not have enough vitamin D over a prolonged period, it can cause bones to soften, break down, or become malformed. As a result, people of all ages end up diagnosed with rickets or osteomalacia. Vitamin D is also noted for assisting with the immune system and strengthening the tissues. With reduced vitamin D levels, the body can become prone to conditions such as cancer and/or autoimmunity.

Research by the Centers for Disease Control and Prevention (CDC) mentions that approximately 25% of the American population is dealing with lower vitamin D levels. In comparison, 8% are noted to be at risk of vitamin D deficiency. It is important to note that the medical rating for “deficiency” is assigned by the Dietary Reference Intake (DRI).

Studies show that a person that’s elderly and/or has a higher BMI (body mass index) is far more prone to vitamin D deficiencies. This can also include individuals that have darker skin pigmentation, may not spend enough time in the sunlight, and/or take medications known for reducing the body’s vitamin D levels. It is necessary to spend at least 5-20 minutes (twice) in the sunlight. If a person is not getting enough sunlight, it is highly recommended to ingest vitamin D through food or supplements.

The Benefit of Getting Tested

It is essential to get out in front of a vitamin D deficiency while adjusting the amount of vitamin D being ingested.

When is it Best to Get Tested?

Vitamin D Testing should be performed as soon as there is a noticeable dip in a person’s phosphorus, parathyroid hormone, and/or calcium levels. This can signal towards an underlying bone condition or disease, which will worsen with a prolonged deficiency. These individuals are at risk of a vitamin D deficiency and should reach out to a qualified medical professional immediately. This test is required before a personalized treatment plan can be administered for osteoporosis. 

A vitamin D test offers:

  • A comprehensive analysis of any underlying bone malformations, bone weakness, and/or abnormalities in calcium/phosphorus/PTH, which is becoming pronounced due to a deficiency
  • Diagnosis of health-related problems associated with a dysfunctional parathyroid gland
  • Screening for individuals at risk of a vitamin D deficiency following the standards set by the National Osteoporosis Foundation and the Institute of Medicine
  • A health status update for relevant medical conditions such as Crohn’s disease and cystic fibrosis, which can cause issues with fat absorption in the human body
  • Monitoring for individuals that have gone through a gastric bypass surgery and may not be absorbing enough vitamin D
  • Guidelines for personalized treatment plans while increasing the amount of calcium, vitamin D, magnesium, and/or phosphorus being ingested

When is Vitamin D Testing Ordered?

25-hydroxyvitamin D

When a blood test reveals abnormalities in a person’s calcium levels and/or the person reveals symptoms associated with a vitamin D deficiency. These symptoms can include bone weakness, bone malformation, fractures (osteomalacia). By testing for 25-hydroxyvitamin D, the specialist can determine how significant the deficiency is.

The test can also be requested if additional factors put the patient at risk of a vitamin D deficiency. This can include a person’s age, amount of exposure to the sun, body mass index, fat malabsorption, breastfeeding, skin pigmentation, and recent gastric bypass surgery. An individual in one or more of these categories can be subjected to a test.

This is a necessary test before a treatment can be set up for osteoporosis.

1,25-dihydroxyvitamin D

When an individual is noted for having some form of kidney disease and/or cannot convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D, this test is administered to determine the cause. In general, this test is not used to determine whether the body has enough calcium. However, it can be used for this purpose. It can also pinpoint the amount of vitamin D in the blood for cases involving lymphoma and sarcoidosis. This has to do with the immune system producing 1,25-dihydroxyvitamin D.

The test may also be administered when vitamin D, phosphorus, calcium, and/or magnesium supplementation is necessary. This can determine how much is needed for the individual’s case.

What do the Test Results Mean?

Vitamin D Testing method is unique in how it is completed and the information it offers. In general, new-age labs will use pre-determined reference intervals during the test. This is done to focus on the lower limit, which looks at the total 25-hydroxyvitamin D in the blood. The upper limit is not tested because toxicity is incredibly rare.

According to the Endocrine Society, a vitamin D deficiency is diagnosed when the 25-hydroxyvitamin D blood level drops below 20 ng/mL (50 nmol/liter).

This also includes a vitamin D insufficiency level of 21-29 ng/ml.

For the U.S. Institute of Medicine, the 25-hydroxyvitamin D level should remain above 20 ng/mL for healthy bone development. It also states that levels beyond 30 ng/mL do not improve a person’s bone health and do not provide enhanced effects. It is important to note, 25-hydroxyvitamin D, and its impact on a person’s overall health varies. In some cases, it is not as clear-cut based on the underlying disorder.

25-hydroxyvitamin D

When there is a lower amount of 25-hydroxyvitamin D in the blood, it can often signal towards inadequate exposure to sunlight and/or reduced vitamin D intake through food sources. It can also signal towards an absorption problem with the person’s intestines. In some cases, certain medications may lead to absorption concerns such as phenytoin (Dilantin).

Studies show that vitamin D deficiency can be associated with certain immune diseases, cancers, and cardiovascular disease.

With a higher amount of 25-hydroxyvitamin D, it may point towards excessive supplementation through food sources or supplements.

1,25-dihydroxyvitamin D

When the amount of 1,25-dihydroxyvitamin D is low, it can lead to health-related issues involving the kidney (i.e., kidney disease). This can often be a sign of early kidney failure in patients.

On the other hand, when the amount of 1,25-dihydroxyvitamin D is high, it means there is too much parathyroid hormone in the blood. This can also mean there is an underlying condition such as lymphoma or sarcoidosis, which can lead to a higher level of 1,25-dihydroxyvitamin D.

When vitamin D and calcium levels are high in the body, they can lead to damaged organs, including the kidney.

When the magnesium levels drop, they can have an added effect on lowering the calcium levels, which impacts parathyroid hormone regulation. This is when it is important to add calcium and magnesium through supplementation.