Medical biochemistry test that measures the level of 25-hydroxy vitamin D3 (25-OH D3) in the blood. Used in the assessment of bone metabolism, muscle function, and overall health.
Indication
- Patients with bone pain, muscle weakness, or frequent falls
- Diagnosis and follow-up of osteoporosis and osteomalacia (softening of the bones)
- Individuals with low sun exposure, dark skin, or those who prefer covered clothing
- Presence of chronic kidney/liver disease or malabsorption (celiac disease, Crohn's disease)
- Evaluation during pregnancy, breastfeeding, or the postmenopausal period
- Dose monitoring in patients receiving vitamin D supplementation
Preparation
- Fasting is generally not required; blood is drawn into a tube according to standard practice
- Any vitamin D supplement taken within the past 24 hours should be reported to the laboratory
- Medications used (corticosteroids, anticonvulsants, etc.) should be communicated to the physician
How it's performed
- A venous blood sample is drawn from the arm (approximately 3-5 mL)
- The sample is transferred to a serum tube and centrifuged
- The 25-OH D3 level is measured using the immunoassay (chemiluminescence) method
- Results are reported in ng/mL
- The result is communicated in writing to the physician/patient
Post-procedure
- Results are usually available the same or the next day
- Levels below 20 ng/mL are considered deficiency, and 20-30 ng/mL insufficiency
- If deficiency is identified, the physician plans the dose and duration; follow-up is recommended 8-12 weeks after treatment
- For those on continuous supplementation, an annual measurement may be sufficient
Risks
- Bruising, tenderness, or a small hematoma at the blood draw site
- Rarely, fainting or short-term pain at the injection site
- The test result must be evaluated together with clinical findings; it does not provide a diagnosis on its own
FAQ
Is fasting required before the vitamin D test?
Most laboratories do not require fasting. Even so, it is recommended to follow the laboratory's instructions before your appointment.
What is done if the result is low?
If the level is below 20 ng/mL, the physician may diagnose deficiency and plan supplementation at an appropriate dose and duration. Follow-up after treatment is important.
How often should the test be repeated?
Follow-up at 8-12 weeks is typical for those receiving deficiency treatment; an annual measurement may be sufficient for those on stable supplementation.
Is it covered by insurance?
When ordered with a physician's indication, it is covered by SGK (Turkish social security); details should be confirmed at laboratory check-in.
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