Lab

Serum Calcium

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Serum Calcium, Corrected Serum Calcium, Ionized Calcium, Free Calcium

  • Physiology
  1. Parathyroid Hormone (PTH) modulates Serum Calcium
    1. PTH rises in response to low calcium
    2. PTH falls in response to high calcium
  2. Vitamin D modulates calcium gastrointestinal absorption
  3. Total body calcium distribution
    1. Skeleton: 98%
    2. Circulating: 2%
      1. Free or ionized Serum Calcium (active): 50%
      2. Albumin-bound Serum Calcium (inactive): 50%
  • Interpretation
  • Normal (normal range varies by individual labs)
  1. Serum Calcium: 8 to 10 mg/dl
  2. Ionized (free) Calcium: 4 to 5.6 mg/dl
  • Interpretation
  • Correcting Serum Calcium for Albumin
  1. No correction needed for Ionized Calcium
  2. Calculation 1
    1. Serum Calcium / (0.6 + (Total Protein/8.5))
  3. Calculation 2
    1. Calcium + ((Normal Albumin - Serum Albumin) x 0.8)
    2. Where normal albumin is often 4.0
  • Interpretation
  • Abnormal
  1. Hypercalcemia
    1. Mild: Serum Calcium 10.5 to 12 mg/dl
    2. Moderate: Serum Calcium 12 to 14 mg/dl
    3. Critical: Serum Calcium 14 mg/dl or higher
  2. Hypocalcemia
    1. Serum Calcium under 8.0 mg/dl