Vitamin D test: what the result means (25-OH D)

Vitamin D is made in the skin under UVB sunlight and also comes from food or supplements. The liver converts it into 25-hydroxyvitamin D — the form the test actually measures, because it stays in the blood the longest and best reflects the body's stores. Vitamin D is needed for calcium absorption and bone health; a long-term deficiency is linked to softened bones, muscle weakness, and, in children, rickets. Results are reported in nmol/l or ng/ml (1 ng/ml = 2.5 nmol/l). The cutoffs that count as deficiency or insufficiency differ between organisations, so a doctor reads the result together with calcium, phosphate and parathyroid hormone levels and your individual risk factors. Excess vitamin D occurs almost only from taking very high supplement doses, and it can raise calcium in the blood.

• With bone pain, muscle weakness, or bone conditions that may be linked to vitamin D deficiency
• In higher-risk groups: over 65, obesity, osteoporosis, little sun exposure, digestive conditions with poorer absorption (Crohn's disease, coeliac disease), kidney or liver disease
• When taking medicines that affect vitamin D metabolism
• To monitor supplement treatment — whether the target level has been reached and there's no excess
• Routine preventive screening in healthy people is generally not recommended

A raised vitamin D level (hypervitaminosis D) is almost always caused by taking very high supplement doses — it's practically impossible to reach excess levels from food or sunlight alone. The danger is that too much vitamin D raises calcium in the blood (hypercalcaemia), which can harm the kidneys, blood vessels and other organs.

• Excessive vitamin D supplement doses taken over a longer period
• A dosing mistake — for example, taking a weekly dose every day

Possible symptoms include nausea, vomiting and loss of appetite, weakness, frequent urination and thirst, and kidney problems with long-term excess. Your doctor will typically also check blood calcium to see whether the excess has already caused hypercalcaemia, review every supplement dose and how long you've taken it, check kidney function, and decide when to repeat the test after adjusting the dose.

Low vitamin D is most often linked to too little sun exposure and too little from food, but it can also come from poor absorption (coeliac disease, Crohn's disease), kidney or liver disease that disrupts the conversion of vitamin D into its active form, certain medicines (phenytoin, phenobarbital, rifampicin), and older age. At Lithuania's latitude, the skin makes almost no vitamin D from October to March.

• Too little sun exposure — especially in autumn and winter, working indoors, or covering the skin
• Too little vitamin D from food
• Poor absorption — coeliac disease, Crohn's disease, other digestive conditions
• Kidney or liver disease that disrupts vitamin D conversion
• Certain medicines: phenytoin, phenobarbital, rifampicin
• Older age — the skin produces less
• Obesity — vitamin D gets stored in fat tissue

Possible symptoms include bone pain, muscle weakness, and fatigue; in children, deficiency can affect growth and bone development. Follow-up typically includes calcium, phosphate and parathyroid hormone to see whether the deficiency has already affected bone metabolism, checking for an underlying condition that impairs absorption, reviewing current medicines, and your doctor deciding on the right supplement dose and when to retest based on your result and risk.

At the Medicina practica laboratory, a vitamin D (25(OH)D) test costs from €19.50 (as of September 2026). Your doctor may order it for higher-risk patients based on indications.