• Information
  1. Normal Calcium Absorption
  2. Causes of Hypocalcemia
  3. Symptoms
  4. Signs
  5. Replacement
• Resources

A. Normal Calcium Absorption

1. Normal absorption is ~20-30%
2. Requires Dihydroxyvitamin D (DHVD)
   1. Vitamin D converted to 25-OH form in liver, then to dihydroxy form in kidney
   2. DHVD stimulates gut absorption of Ca2+ and HPO4(-2)
3. Decreases with age
4. May increase with food (up to ~500mg elemental calcium per meal)

B. Causes of Hypocalcemia

1. Endocrinopathy
   1. Hypoparathyroidism (permanent or transient)
   2. Vitamin D Deficiency or Resistance (Rickets) [5]
   3. Rule out autoimmune polyendocrinopathy sydnrome
   4. Pseuohypoparathyroidism
2. Renal Disease
   1. Most commonly with chronic renal disease
   2. Renal losses - usually due to loop diuretic effects
3. Pancreatitis
   1. Mainly in severe acute as well as in chronic pancreatitis
   2. Due to calcium saponification
4. Calcium Malabsorption
   1. Usually associated with full metabolic bone disease (MBD)
   2. MBD broadly refers to vitamin D deficiency and hypocalcemia
   3. Frequently seen with a variety of malabsorption syndromes including malignancies
   4. Crohns' Disease
   5. Gluten sensitive enteropathy (Celiac Disease) [2]
5. Defiency of Calcium in Diet [3]
   1. Average American diet intake 800mg/day for an adult
   2. Recommended daily allowance (RDA) are 800mg/d for children 4-8 years old
   3. RDA children 9-18 1300mg/d
   4. RDA adults up to 50 years old 1000mg/d (includes pregnant and lactating women)
   5. RDA adults >50 years old 1200mg/d (including those with osteoporosis)
   6. Should be taken with vitamin D to insure absorption
   7. Vitamin D+calcium supplements increase bone mineral density and reduce fracture risk
6. Other
   1. Rhabdomyolysis
   2. Hypomagnesemia
   3. Septic shock
7. Genetic - mutations in calcium sensing receptor [4]

C. Symptoms

1. Tetany
   1. Most common presentation of severe hypocalcemia
   2. Alkalosis can also cause tetany
2. Muscle Fatigue
3. Paralytic Ileus
4. Bradycardia
5. Hypotension
6. Change in Mental Status
7. Cataracts
8. Soft Tissue Calcium Deposition
   1. A rise in serum calcium X phosphate product >70 leads to soft tissue deposition
   2. Calcium phosphate salts are deposited in soft tissues
   3. This leads to hypocalcemia and potentially organ damage

D. Signs

1. Chvostek's Sign
   1. Tap over facial nerve in front of ear
   2. Positive result is twitching over the facial muscles, especially upper lip
   3. 5-10% of normal population may have a positive test
2. Trousseau's Sign
   1. Blood pressure cuff inflated over upper arm
   2. Positive test: hand flexing at wrist and fingers flexed at MCP and extended at ICP joints
3. Prolonged QT interval on ECG, usually with bradycardia
4. Hypotension may occur

E. Replacement [3]

1. Oral Calcium (often with Vitamin D 200U per tablet)
   1. Several formulations are available
   2. Calcium Carbonate 600mg elemental Ca per tablet, 2 / day - increased side effects
   3. Calcium Citrate 315mg Ca per tablet, 3 / day - well absorbed
   4. Calcium Phosphate 600mg elemental Ca per tablet, 2 / day
2. Calcium Gluconate IV (requires first pass through liver)
3. Calcium chloride should generally not be given as it can cause acute vessel occlusions

Resources

Corrected Serum Calcium for Albumin

References

1. Bushinsky DA and Monk RD. 1998. Lancet. 352(9124):306
2. Shaker JL, Brickner RC, Findling JW, et al. 1997. Arch Intern Med. 157(9):1013
3. Calcium Supplements. 2000. Med Let. 42(1075):29
4. Pearce SHS, Williamson C, Kifor O, et al. 1996. NEJM. 335(15):1115
5. Wharton B and Bishop N. 2003. Lancet. 362(9393):1389