Carbon Monoxide Headquarters

Carbon Monoxide Poisoning

The Essentials of Carboxyhemoglobin:

Many errors in clinical medicine revolve around the misunderstanding of COHb - physicians more often than not fail to diagnose CO poisoning when it is actually present. Many more errors in forensic medicine revolve around the misunderstanding of COHb - physicians and others order COHb tests too late which are certain to show low/normal COHb levels when people have obviously been exposed to CO. The litigation of CO poisoning cases in many many instances is thwarted or crippled by a misunderstanding of COHb.


Please Know:

  • Fact - COHb has a short 1/2-life in the body, 4-5 hours. Half is gone in 4-5 hours; in most cases the blood CO level is back to background in 24 hours.

  • Fact - "Back-calculation to time zero (to) can be done by an expert after some hours; beyond that point increasing error may creep in.

  • Fact - Many tests can be run in people suspected of CO poisoning, but the COHb test is among the most important.

    What to Do: -

    If you, your furnace maintenance man, your physician, etc. suspect you have been exposed to CO, INSIST that blood be drawn immediately (venous will be as good as arterial blood and it is a lot less painful to obtain). Once drawn, blood for COHb assay can be stored for days/weeks without loss of testing accuracy. If medical personnel or others tell you the draw time can be delayed, they are wrong! Refer them to this website and the webmaster for re-education.

    Also, VERY IMPORTANT - First: attempt to keep track of exactly how long it was from the time you left the site of the CO exposure until your blood was drawn. Second: keep track of how long and when you were given 100% oxygen by EMS or ER physicians before your blood was drawn. While this may be challenging if you are in an altered state of consciousness from the CO, the numbers are invaluable later in re-constructing your to COHb concentration.

    Please Note: -

    Breathlyzer Equipment can be used to determine blood COHb level with great accuracy. The test does not require that blood be drawn.

    Pulse Oximeters, as found in EMS vans and in hospital ERs, should not be use to determine whether you have abnormally high levels of CO in your blood. They lie!

    There are many Reasons Why Carboxyhemoglobin may be Unexpectantly Low. The first two in the linked list are the most relevant. Do not be the victim of a screw-up in this important diagnostic test.

    * If the blood is drawn many hours after leaving the site of the poisoning, it may be possible to back-calculate to determine the COHb level at to. This depends on the length of time (number of 1/2 lives) between time of blood draw and to, and on the difference in COHb between the measured value and background COHb value.

    ...... last changed 01/17/02

    To COHQ Main Index