Definition: A serum calcium level < 8.5 mg/dL or an ionized calcium level < 2.0 mEq/L
Background
- Exists in two states
- Free ionized form (approx. 50%)
- Bound to other molecules (primarily albumin)
- Ionized Ca2+ concentration is inversely proportional to pH
- Ca2+ metabolism
- Vitamin D: aids in intestinal Ca2+ absorption
- Parathyroid hormone (PTH)
- Increases renal Ca2+ reabsorption
- Arbitrates Vit D stimulated intestinal Ca2+ absorption
- Mobilizes Ca2+ from bone
- Calcitonin
- PTH antagonist
- Inhibits renal Ca2+ reabsorption
- Inhibits Ca2+ mobilization from bone
- Ca2+ plays numerous critical roles including muscle contraction (skeletal and smooth), clotting factor activity and nerve conduction
Causes
- Hypoalbuminemia (Ca2+ bound to albumin)
- Hypoparathyroidism
- Chronic renal failure
- Electrolyte disorders: Hypomagnesemia, Hyperphosphatemia
- Abnormal cell destruction: tumor lysis syndrome, rhabdomyolysis
- Severe pancreatitis
- Drugs: Calcitonin, phosphate, bisphosphonates
- Tox: HFl acid burn
- Massive blood transfusion (due to citrate in blood products)
Clinical Manifestations
- Cardiac Effects
- Hypotension
- QTc prolongation
- Congestive heart failure
- Cardiovascular collapse (severe hypocalcemia)
- Neuromuscular Effects
- Muscle cramping
- Paraesthesias
- Tetany
- Chvostek’s sign: facial muscle twitching with tapping over facial nerve (commonly seen in patients without hypocalcemia)
- Trousseau’s sign: carpal spasms induced by inflation of a blood pressure cuff 20 mm Hg above systolic BP X 3 minutes
- Other symptoms
- Altered mental status
- Coarse hair
- Cataracts
- Poor dentition
- Dry skin
- Laryngospasm
- Bronchospasm, wheezing
- Fatigue
Diagnosis
- Serum calcium < 8.5 mg/dL
- Correct for hypoalbuminemia:1 g/dL drop in serum albumin below 4 g/dL = 0.8 mg/dL drop in serum calcium
- 50% of serum calcium is protein bound, 50% ionized (free)
- Ionized calcium < 2.0 mEq/L
- More accurate assessment as no correction required
Management
- Asymptomatic/Minimally symptomatic
- Oral supplementation with calcium salts (i.e. calcium carbonate or calcium citrate)
- Disposition: Discharge home with outpatient follow up
- Moderate/Severe Symptoms
- Intravenous calcium supplementation: 100-300 mg Ca2+ raises serum Ca2+ by 0.5 – 1.5 mEq
- Calcium Chloride (CaCl2)
- Standard “ampule”: 10 ml of 10% CaCl2 = 270 mg of Ca2+
- Caustic to veins – should be administered in large peripheral IV or central line preferably
- Calcium Gluconate
- Standard “ampule”: 10 ml of 10% CaGluconate = 90 mg of Ca2+
- For equivalent dosing to CaCl, give 3 “amps” of CaGluconate
- Despite classic teaching, CaCl2 is not more bioavailable than CaGluconate and does not raise serum Ca2+ faster. (Hayes 2013)
- Disposition: Admission to monitored setting if ongoing intravenous repletion (bradycardia and hypertension may occur)
- Consider giving prophylactic calcium supplementation in patients receiving massive transfusions.
- Magnesium supplementation: Concomitant hypomagnesemia is common.
Take Home Points
- Severe hypocalcemia can cause hypotension and QTc prolongation leading to Torsades de Pointes.
- Treat moderate to severe symptoms and any EKG changes with IV calcium salts
- Always search for and treat the underlying cause of hypocalcemia
References
Pfenning CL, Slovis CM: Electrolyte Disorders; in Marx JA, Hockberger RS, Walls RM, et al (eds): Rosen’s Emergency Medicine: Concepts and Clinical Practice, ed 8. St. Louis, Mosby, Inc., 2014, (Ch) 125: p 1636-53.
Hayes BD. (2013, July 2). Mythbuster: Calcium Gluconate Raises Serum Calcium as Quickly as Calcium Chloride [ALiEM]. Retrieved from http://www.aliem.com/posts/
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LITFL: Hypocalcemia
LITFL: Hypocalcaemia