Vitamin D (25(OH) cholecalciferol)

Vitamin D testing is a laboratory study that allows determining the level of 25(OH)-cholecalciferol in the blood.

This indicator reflects the total intake of vitamin D from food, supplements, and sunlight, as well as the body’s ability to absorb and convert it into its active form.

The test helps identify both deficiency and excess of vitamin D, which is important for assessing calcium and phosphorus metabolism and the overall condition of the bone and immune systems.

When to get tested

Determining vitamin D levels is indicated in the following cases:

• frequent colds and viral infections;
• chronic fatigue, apathy, decreased concentration;
• muscle and bone pain, cramps, brittleness of bones;
• growth retardation in children or risk of osteoporosis in adults;
• pathologies of the thyroid and parathyroid glands;
• excess weight, diabetes, autoimmune diseases;
• taking calcium, hormone, or vitamin D supplements for therapy monitoring.

Preparation for the test

Blood for the study is taken from a vein, preferably in the morning, on an empty stomach.

It is recommended not to eat or take vitamin D supplements for 8–12 hours before the procedure.

It is advisable to exclude fatty foods and alcohol a day before the test, as well as to limit physical activity.

Normal values and interpretation

The reference values for 25(OH)D levels may vary in different laboratories, but usually are:

• less than 20 ng/ml — severe deficiency;
• 20–30 ng/ml — insufficiency;
• 30–60 ng/ml — optimal level;
• above 100 ng/ml — possible excess requiring dosage adjustments.

The test results are evaluated by a doctor considering age, body weight, season, concomitant diseases, and supplement intake.

Why monitor vitamin D levels

Monitoring vitamin D is important not only when deficiency is suspected but also during preventive observation.

Excessive intake of supplements can lead to hypercalcemia, kidney and vascular dysfunction.

An optimal level of vitamin D supports bone strength, immunity, hormonal balance, and good mood.

Conclusion

Vitamin D testing is a simple and informative way to assess whether the body is receiving enough of this important nutrient.

Regular checks help adjust diet, supplement dosages, and prevent complications related to both deficiency and excess of vitamin D.