Overview of Vitamin D (25-OH)
What is Vitamin D (25-OH)?
Preparation for Vitamin D (25-OH)
- No special preparation required
Why Get Tested for Vitamin D (25-OH)?
To determine vitamin D deficiency when calcium level is low or a person has symptoms of vitamin D deficiency such as bone malformation in children (rickets) and bone weakness, softness, or fracture in adults (osteomalacia).
· Before starting therapy for osteoporosis.
· To monitor the adequacy of treatment in patients who are receiving Vitamin D supplements, calcium, phosphorus, and/or magnesium supplements.
· Diagnose/monitor problems with the parathyroid gland functioning since the parathyroid hormone (PTH) is essential for vitamin D activation.
· Monitor the health status of individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn’s disease and in patients who have undergone gastric bypass surgery.
Understand more about Vitamin D (25-OH)
Two forms of vitamin D can be measured in the blood, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D. The 25-hydroxyvitamin D is the major form found in the blood and is the relatively inactive precursor to the active hormone, 1,25-dihydroxyvitamin D. Because of its long half-life and higher concentration, 25-hydroxyvitamin D is commonly measured to assess and monitor vitamin D status in individuals.
The 25-hydroxyvitamin D test is done to determine the level of Vitamin D in your blood, whether it is low or higher than normal. A low blood level of 25-hydroxyvitamin D can be seen if a person is not getting enough exposure to sunlight or enough dietary vitamin D to meet his or her body's demand or if there is a problem with its absorption from the intestines (cystic fibrosis, Crohn’s disease, who have undergone gastric bypass surgery). Sometimes, drugs used to treat seizure (Phenytoin) can cause Vitamin D deficiency by interfering with transformation to 25-hydroxyvitamin D in the liver. Severe liver and kidney diseases can also cause vitamin D deficiency. A high level of 25-hydroxyvitamin D usually reflects excess supplementation of the vitamin.
What Results of Vitamin D (25-OH) mean?
Low vitamin D level than normal reference range indicating vitamin D deficiency can be because of less sun exposure, dietary deficiency or due to decreased absorption from the intestine.
High vitamin D level than normal reference range indicates vitamin D intoxication and is usually due to excess supplementation of the vitamin.
The normal range of vitamin D is measured as nanograms per milliliter (ng/mL) or nmol/L and can vary from lab to lab.
Reference range (ng/mL)
Mild to moderate deficiency
· The assay measures both vitamin D2 (Ergocalciferol) and vitamin D3 (Cholecalciferol) metabolites of vitamin D.
· There can be seasonal variation in 25 (OH) vitamin D level, with values being 40-50% lower in winter than in summer. It is also influenced by sunlight, latitude, skin pigmentation, sunscreen use, and hepatic function.
· 25 (OH) vitamin D levels can vary with age
· 25 (OH) vitamin D level is increased during pregnancy.
Patient Concerns about Vitamin D (25-OH)
Frequently Asked Questions about Vitamin D (25-OH)