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Test Catalog

Test ID: COHBB    
Carbon Monoxide, Blood

Useful For Suggests clinical disorders or settings where the test may be helpful

Verifying carbon monoxide toxicity in cases of suspected exposure

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Carbon monoxide (CO) poisoning causes anoxia, because CO binds to hemoglobin with an affinity 240 times greater than that of oxygen, thus preventing delivery of oxygen to the tissues. Twenty percent saturation of hemoglobin induces symptoms (headache, fatigue, dizziness, confusion, nausea, vomiting, increased pulse, and respiratory rate). Sixty percent saturation is usually fatal. This concentration is reached when there is 1 part CO per 1,000 parts air.


Carboxyhemoglobin diminishes at a rate of about 15% per hour when the patient is removed from the contaminated environment.


The most common cause of CO toxicity is exposure to automobile exhaust fumes. Significant levels of carboxyhemoglobin can also be observed in heavy smokers. Victims of fires often show elevated levels from inhaling CO generated during combustion. Susceptibility to CO poisoning is increased in anemic persons.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Normal Concentration

Non-Smokers: 0-2%

Smokers: < or =9%

Toxic concentration: > or =20%

Interpretation Provides information to assist in interpretation of the test results

Normal Concentration

Non-Smokers: 0-2%

Smokers: < or =9%

Toxic concentration: > or =20%

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

No significant cautionary statements

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Fourth edition. Edited by CA Burtis, ER Ashwood, DE Bruns, St. Louis, MO, Elsevier Saunders, 2006

2. Vreman HJ, Stevenson DK, Zwart A: Analysis for carboxyhemoglobin by gas chromatography and multicomponent spectrophotometry compared. Clin Chem 1987;33:694-697

3. Kunsman GW, Presses CL, Rodrigues P: Carbon monoxide stability in stored postmortem blood samples. J Anal Toxicol 2000;24:572-578

4. Hampson NB: Stability of carboxyhemoglobin in stored and mailed blood samples. Am J Emerg Med. 2008 Feb;26(2):191-195

5. Operator's Manual, AVOXimeter 4000 Whole Blood Oximeter, AP4001, International Technidyne Corporation,  Edison, NJ, 10/2007