Feb 12, 2026Biomarker Testing Before Supplementing: B12, Vitamin D, Homocysteine, Ferritin, and CRPSupplementing without baseline testing is guesswork. Vitamin D, B12, folate, ferritin, homocysteine, and hs-CRP are the most actionable starting points. This guide explains what each test reveals, what ranges mean, and which supplements to prioritize based on results.