Vitamin-D Selbsttest: which blood markers matter?

For a vitamin D self-test, the key blood marker is 25-hydroxyvitamin D (25(OH)D), also called calcidiol. This is the storage form of vitamin D and the most reliable indicator of overall vitamin D status. Some home tests incorrectly measure only vitamin D3, which is insufficient. The analysis is typically done via dried blood spot and subsequent LC-MS/MS or immunoassay. Important caveats: a single measurement reflects current status but not long-term adequacy; reference ranges vary – the Endocrine Society recommends 30–50 ng/mL (75–125 nmol/L), while the IOM considers 20 ng/mL sufficient. Self-tests can help rule out deficiency, but abnormal results should be confirmed by a physician. Genetic variants like VDR have only minor effects on blood levels and are not included in standard self-tests. The evidence for 25(OH)D as a biomarker is strong (human-strong), but the accuracy of home tests depends on the laboratory. Markers such as calcium or PTH are not measured in typical self-tests, though they are relevant for calcium metabolism. Overall, a vitamin D self-test is a reasonable screening tool, but not a substitute for professional medical evaluation.