Vitamin D (25-Hydroxyvitamin D)
Definition
Most vitamin D blood tests measure the level of 25-hydroxyvitamin D [25(OH)D], formed after conversion in the liver, because this is the most accurate way to see whether the body has enough vitamin D.
Purpose
Ordered in diagnosed bone diseases (osteoporosis, rickets, osteomalacia). Investigated when deficiency symptoms are present (bone pain, muscle weakness, fractures). Checked in high-risk individuals (limited sun exposure, malabsorption disorders, kidney/liver disease, certain medications) and in breastfed infants.
Results
Results are evaluated in four categories:
| Category | Meaning |
|---|---|
| Deficient | Very low level affecting bones and overall health |
| Insufficient | Low level that can weaken bones |
| Sufficient | Adequate for bone and overall health |
| Toxic | Very high level resulting from excessive supplement use |
Normal Values
Laboratory-specific, see the reference range on your report.
Risks and Limitations
Routine vitamin D testing is not recommended for everyone. Physicians decide who should be tested; universal screening is not recommended. This is an important note regarding the decision to include vitamin D in checkup packages.