Vitamin D, 25-Hydroxy, Total, Immunoassay

Alternate Test Name: ,25-Hydroxyvitamin D2 

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: 25-hydroxyvitamin D Test, Vitamin D 25-Hydroxyvitamin 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 bones and teeth. 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. 

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. 

Lab tests often ordered with a Vitamin D test: 

Conditions where a Vitamin D test is recommended:

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 may not be able to absorb vitamin D adequately or have had gastric bypass surgery 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? 

Even though 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 source of vitamin D 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.