Hypocalcemia
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Contents |
Introduction
- Albumin binds 45% of serum Ca+2, thus a low Ca+2 in the face of hypoalbuminemia may not reflect true hypocalcemia. If free (ionized) Ca+2 is normal, then no disorder of calcium metabolism is present. If ionized Ca+2 cannot be measured, a corrected calcium can be estimated by adding 0.8 mg/dL for every g/dL decrease in serum albumin below 4.0 g/dL.
- The percentage of calcium bound to albumin varies, especially in critically ill patients, particularly at extremes of pH & osmolality. Acidemia increases ionized Ca+2 whereas alkalemia dimimishes it. In these conditions the correction formula may not be useful.
Etiology
- (causes of true hypocalcemia)
- renal failure
- hypoparathyroidism
- surgical excision or vascular injury to the parathyroids during neck surgery
- hypomagnesemia (severe)
- hypermagnesemia
- pancreatitis (acute)
- hyperphosphatemic states
- osteoblastic metastases
- pseudohypoparathyroidism ( PTH resistance)
- citrated blood transfusions (multiple)
- idiopathic (common in critically ill patients)
- sepsis syndrome
- hungry bone syndrome
- acute respiratory alkalosis
- pharmacologic causes:
-
- hypocalcemic agents used to treat Paget's disease or hypercalcemia
Clinical-manifestations
- Trousseau's sign
- Chvostek's sign
- mild symptoms include perioral numbness & paresthesias in extremities
- musculoskeletal manifestations
- central nervous system manifestations
- cardiac manifestations:
- manifestations of chronic hypocalcemia
Laboratory
- serum calcium
- serum albumin
- ionized calcium if indicated
- serum Mg+2
- serum creatinine to rule out renal insufficiency
- serum parathyroid hormone ( serum PTH) if true hypocalcemia
- serum 25-hydroxyvitamin D3
- serum 1,25-dihydroxyvitamin D3
- serum phosphorus
Diagnostic-procedures
Differential-diagnosis
-
- hypocalcemia, hyperphosphatemia, elevated serum PTH, normal serum 25-hydroxyvitamin D3
- hypocalcemia, hyperphosphatemia, elevated serum PTH, low serum calcitriol
- hypocalcemia, bone tenderness or fibromyalgia-like syndrome
- impaired PTH secretion/ PTH resistance
- hypocalcemia, magnesium deficiency
- hypocalcemia after parathyroidectomy
Management
- acute
- calcium gluconate (10%) 2 ampules 20 mL IV over 10 minutes, followed by infusion of 60 mL of calcium gluconate in 500 mL D5W (1 mg/mL) at 0.5-2.0 mg/kg/ hr
- correct hypomagnesemia
- monitor ECG in patients taking digoxin, since hypocalcemia potentiates digitalis toxicity
- chronic (see hypoparathyroidism)
- generally well tolerated if mild
- supplemental calcium
- vitamin D or 1,25-dihydroxyvitamin D3 ( calcitriol)
-
- 0.25 ug PO QD (initially)
- 0.5-2.0 mg PO QD (maintenance)
- dose may be increased at 2-4 week intervals
- indicated with renal failure ( hydroxylation of 25-OH vitamin D occurs in the kidney)
- 25-OH vitamin D3 indicated in liver failure (vitamin D hydroxylated to 25-OH vitamin D in liver)
- vitamin D
- if hypercalcemia develops, stop vitamin D, then restart at a lower dose
- calcium acetate ( Phoslo) as needed to maintain serum phosphorus < 6.5 mg/dL
- thiazide diuretics to inhibit urinary Ca+2 excretion
- correct magnesium deficiency
- hypocalcemia difficult to correct if hypomagnesemia
More General Terms
Additional Terms
- calcium (Ca+2) in serum
- Chvostek's sign
- hungry bone syndrome
- hypercalcemia
- hypoparathyroidism
- magnesium (Mg+2) in serum
- pancreatitis
- parathyroid hormone in serum/plasma
- pseudohypoparathyroidism
- renal failure; kidney failure
- Trousseau's sign
References
- Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 495
- Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 665-667
- Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 215-217
- Medical Knowledge Self Assessment Program (MKSAP) 11, 14, 15, American College of Physicians, Philadelphia 1998, 2006, 2009
