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%
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
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
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

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 5/10/2008. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.