Vitamin D Test: which blood markers matter?

For a vitamin D test, the key blood marker is 25-hydroxyvitamin D (25(OH)D). This storage form reflects total vitamin D status over weeks and is the standard recommended by the Endocrine Society and the German Nutrition Society (DGE). Some tests also measure 1,25-dihydroxyvitamin D (1,25(OH)2D), the active hormone, but it fluctuates rapidly and is not suitable for assessing overall deficiency – it is only indicated in kidney or calcium metabolism disorders. Additional markers like parathyroid hormone (PTH) and calcium can provide functional context but are rarely included in at-home kits. Caveats: a single measurement is a snapshot; seasonal variation, supplementation, BMI, and skin type affect levels. The evidence for 25(OH)D’s role in bone health is strong (human-strong), but routine screening in healthy adults without risk factors is not universally recommended. MyBody-X’s vitamin D test measures 25(OH)D. Interpretation should be done with a healthcare professional, as reference ranges differ by lab and clinical goal. Marketing claims about ‘optimal’ levels often oversimplify the science.