What can the Vitamin-D Selbsttest tell you — and what not?

The Vitamin-D Selbsttest (e.g., from MyBody-X) measures 25-hydroxyvitamin D levels from a fingerstick blood sample. It can indicate a possible deficiency or excess but cannot diagnose a medical condition. Home tests are less accurate than venous blood draws in a lab. Vitamin D levels fluctuate seasonally and can be affected by inflammation. The test does not reveal the underlying cause of a deficiency (e.g., kidney function, malabsorption) or assess bone health. For clinical decisions (e.g., suspected osteoporosis), a doctor's evaluation is required. Evidence is based on general lab practice, not product-specific trials. Caveat: Do not self-treat with high-dose vitamin D without medical supervision.