Vitamin D, 25-Hydroxy (Total)

This test measures the total amount of 25-hydroxyvitamin D in your blood, which is the main circulating form of vitamin D and the best indicator of your overall vitamin D status. It includes both vitamin D2 (from some foods and supplements) and vitamin D3 (made in your skin with sunlight and found in certain foods and supplements).

Your body converts vitamin D from sun exposure, diet, and supplements into 25-hydroxyvitamin D in the liver. Levels of this form change slowly and reflect your vitamin D stores over weeks to months. It is different from the active hormone form, which is used by tissues but does not reliably show your overall vitamin D balance.

Vitamin D supports healthy bones and muscles by helping your body manage calcium and phosphate. It also plays a role in immune function and overall well-being. Clinicians use this test to check for low vitamin D, to monitor supplementation, and to evaluate conditions that affect bone health.

You might have this test if you have limited sun exposure, darker skin, are older, have a history of falls or fractures, or have conditions that affect absorption or metabolism such as celiac disease, inflammatory bowel disease, liver disease, or kidney disease. It is also used to guide dosing of supplements and to avoid levels that are too high.

Your healthcare provider will interpret your result in the context of your symptoms, risk factors, and other lab tests. If your level is lower than expected, they may discuss diet, safe sun exposure, or supplementation, and may recheck your level after some time to see how it responds. If your level is higher than expected, they may review supplement doses and look for medical causes.

Follow-up can include checking calcium, phosphorus, parathyroid hormone, kidney function, or other bone health markers. Do not change supplements on your own; review your current intake from all sources with your clinician so you can adjust safely and reach a stable, healthy level.