Vitamin D Test

About this test

This test measures your blood level of 25-hydroxyvitamin D — the main storage form of vitamin D in the body and the best indicator of your overall vitamin D status. Vitamin D is essential for calcium and phosphorus absorption (which are critical for bone strength), immune system regulation, muscle function, and mood. Many studies also link adequate vitamin D to reduced risk of certain chronic diseases.

Vitamin D deficiency is one of the most common nutritional deficiencies in the world, affecting people of all ages and backgrounds. It is particularly common in people who spend little time outdoors, live in northern climates, have darker skin, are overweight, or are older. Deficiency is straightforward to identify with this test and usually easy to correct with supplementation.

Components

• 25-Hydroxyvitamin D (Total): Reflects your combined vitamin D stores from sun exposure, food, and supplements. Levels are generally interpreted as follows: below 20 ng/mL is considered deficient; 20–29 ng/mL is often considered insufficient; 30–100 ng/mL is generally regarded as sufficient. Levels above 100–150 ng/mL may indicate toxicity from excessive supplementation. Your clinician will recommend the appropriate supplementation dose and follow-up interval based on your result.

Who is this test for?

Vitamin D deficiency is extremely common, especially in people who spend limited time outdoors, live in northern latitudes, have darker skin, are obese, or are over 65. The Endocrine Society recommends testing for individuals at risk of deficiency, including those with bone pain, muscle weakness, fatigue, or a history of falls or fractures. People with conditions that affect fat absorption (such as Crohn's disease or celiac disease) are also at increased risk of low vitamin D.