UMEM Educational Pearls

Category: Critical Care

Title: Hypocalcemia

Posted: 2/3/2010 by Evadne Marcolini, MD (Emailed: 2/9/2010) (Updated: 1/18/2022)
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  • Total body calcium consists of about half biologically active (ionized) and half inactive (80% bound to albumin and 20% to other ions)
  • hypocalcemia caused by hypoalbuminemia is physiologically insignificant, and correction factors are not accurate or reliable
  • The best way to measure true active calcium is to order an ionized calcium level

There are several conditions that alter ionized calcium levels, including:

  • alkalosis (increases binding to albumin)
  • gas bubbles in the sample (false lowering of calcium)
  • anticoagulants (must be collected in a red top tube)
  • blood transfusions (binding to citrate)
  • cardiopulmonary bypass
  • drugs (aminoglycosides, cimetidine, heparin, theophylline)
  • fat embolism
  • hypomagnesemia (correcting mg levels may preclude need for Ca repletion)
  • pancreatitis (several mechanisms, poor prognosis)
  • renal insufficiency (impaired phosphate retention)
  • sepsis

The bottom line is to measure ionized calcium, and consider all other factors that can be contributing to hypocalcemia in addition to repleting it.