• measurement of blood concentration of various forms of haemoglobin


  • a device that uses spectrophotometry to measure relative blood concentrations of oxyhemoglobin, carboxyhemoglobin, methemoglobin, and reduced haemoglobin


  • a laboratory test involving a blood sample heated to 37 C and subjected to light of various length and assesses absorption spectra.
  • does not require pulsatile flow
  • measures MetHb, COHb and other forms of Hb
  • uses many other wavelengths


  • measures either venous, arterial or capillary oxygenation


Causes of HIGH Co-oximetery and LOW Pulse Oximetry Readings

  • Poor peripheral perfusion
  • Ambient light
  • Poor probe contact
  • Dyes (e.g. methylene blue)
  • Tricuspid regurgitation (and other causes of venous pulsations)

Causes of LOW Co-oximetry and HIGH Pulse Oximetry Readings

  • COHb
  • MetHb
  • Radiofrequency interference
  • Leukocyte larceny (oxygen consumption by cells in the collection tube, may also occur in situations such as severe thrombocytosis)

FOAM and Web resources

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

One comment

  1. Good article..
    Want to know how meth Hb cause low cooxymeter reading compare to pulse oxymeter. Bcz usually pulse oxy shows low values in meth hemoglobin ema.

    Thank you

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