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Vitamin D (25-Hydroxy) Blood Test

The Vitamin D Blood Test measures 25-hydroxy vitamin D [25(OH)D], the most reliable marker of vitamin D status. Vitamin D supports calcium and phosphorus absorption for bone health and also plays roles in muscle function, immune health, blood pressure, and insulin regulation. Because the active hormone form can appear normal even when stores are low, 25(OH)D is preferred for assessing deficiency.

Why Measure Vitamin D?

  • Bone & muscle support: Assess risks related to bone density and muscle performance.
  • Immune & metabolic context: Gauge status in conditions affecting immunity and glucose regulation.
  • Identify risk groups: Older adults, people with darker skin, individuals with obesity, vegans, and pregnant women may be at higher risk for low vitamin D. 

How the PlexusDx Test Works

  • At-home collection: Finger-prick sample with prepaid return mailer.
  • Fast results: Typically ~2 business days after the lab receives your sample.
  • Direct-to-consumer & HSA/FSA: Order online without a doctor’s order; HSA/FSA accepted. 

Understanding Results

Reference ranges vary by lab. Your clinician considers 25(OH)D alongside calcium, parathyroid function, and clinical history (e.g., absorption disorders) to guide diet, sun exposure, or supplementation.

FAQs

Do I need to fast?
No fasting is typically required; follow the provided kit instructions. 

How can I improve low vitamin D?
Depending on your clinician’s guidance: sensible sun exposure, dietary sources (fatty fish, fortified foods), and/or supplementation.