COHBB - Clinical: Carbon Monoxide, Blood

Test Catalog

Test Name

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

The toxic effects of carbon monoxide can be seen above 20% carboxyhemoglobin. It must be emphasized that the carboxyhemoglobin concentration, although helpful in diagnosis, does not always correlate with the clinical findings or prognosis. Factors other than carboxyhemoglobin concentration that contribute to toxicity include length of exposure, metabolic activity, and underlying disease, especially cardiac or cerebrovascular disease. Moreover, low carboxyhemoglobin concentrations relative to the severity of poisoning may be observed if the patient was removed from the carbon monoxide-contaminated environment a significant amount of time before blood sampling.

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 Recommendations for in-depth reading of a clinical nature

1. Langman LJ, Bechtel L, Holstege CP: Clinical toxicology. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Edited by CA Burtis, ER Ashwood, DE Bruns. 5th edition. Elsevier Saunders, St. Louis, MO. 2012 pp 1109-1188

2. Disposition of Toxic Drugs and Chemicals in Man. 10th edition. Edited by RC Baselt. South Beach CA, Biomedical Publications, 2014

3. Instruction Manual: ABL80 FLEX CO-OX analyzer-OSM version, Radiometer Medical ApS, Denmark, 2016