🧬 Vitamin Tests Explained: D 25OH, D3 & B12

1. Vitamin D 25-OH (25-Hydroxyvitamin D)

• 🧪 Other Names:
  • 25-OH Vitamin D
  • Calcidiol
  • Main test for assessing Vitamin D status
• ✅ Fasting Required: Yes (8–10 hours preferred)
• 🧠 Target Organs: Bones, immune system, parathyroid glands
• 📊 Function:
  • Regulates calcium and phosphate absorption
  • Essential for bone mineralization
  • Modulates immune function
• 📉 Deficiency Causes:
  • Rickets (children)
  • Osteomalacia / osteoporosis (adults)
  • Fatigue, muscle weakness, immune dysfunction
• ✅ Normal Range:
  • 30–100 ng/mL
  • Deficient: < 20 ng/mL
  • Insufficient: 20–30 ng/mL
• 🧪 Recommended with:
  • Serum calcium, phosphate, PTH
  • Bone density scan (if chronic low levels)
  • Vitamin D3 (active form) in special cases

2. Vitamin D3 (Cholecalciferol)

• 🧪 Functionally: One of the two major forms of Vitamin D (D3 = animal-based; D2 = plant-based)
• 🧠 Biology:
  • Vitamin D3 is converted to 25-OH Vitamin D in the liver → then to active 1,25(OH)₂D in the kidney
• 🧪 Used For:
  • Supplement formulation, not routinely measured in blood
  • Blood testing is not standardized or clinically necessary in most labs
• ⚠️ Note: If someone says “test my Vitamin D3,” they likely mean 25-OH Vitamin D, which is the standard
• 🧪 Occasional measurement in:
  • Complex deficiency cases
  • Patients with kidney disease or disorders of conversion
• ✅ Use 25-OH Vitamin D as the clinical standard test

3. Vitamin B12 (Cobalamin)

• ✅ Fasting Required: Yes (8–10 hours)
• 🧠 Target Organs: Nervous system, red blood cell production, DNA synthesis
• 📊 Function:
  • Supports nerve cell health
  • Prevents megaloblastic anemia
  • Helps energy metabolism and mood regulation
• 📉 Deficiency Symptoms:
  • Fatigue, tingling/numbness (peripheral neuropathy)
  • Memory loss, mood changes, balance issues
  • Macrocytic anemia (large RBCs)
• ✅ Normal Range: 200–900 pg/mL
  • Deficient: < 200 pg/mL
  • Borderline: 200–350 pg/mL
• 🧪 Recommended with:
  • Folic acid (often co-deficient)
  • Homocysteine and Methylmalonic Acid (MMA) (functional markers)
  • CBC (to assess anemia)
  • Intrinsic factor antibodies (in suspected pernicious anemia)

📊 Summary Comparison

🧪 Recommended Profiles