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Test Code COHBB Carbon Monoxide, Blood

Reporting Name

Carbon Monoxide, B

Useful For

Verifying carbon monoxide toxicity in cases of suspected exposure

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Whole Blood EDTA

Advisory Information

This test is not available for autopsy or cadaver specimens.

Specimen Required

Container/Tube: Lavender top (EDTA)

Specimen Volume: 1 mL

Collection Instructions: Avoid exposure of specimen to atmosphere.

Specimen Minimum Volume

0.1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood EDTA Ambient (preferred) 14 days
  Frozen  14 days
  Refrigerated  14 days

Reference Values

Normal Concentration

Non-Smokers: 0-2%

Smokers: ≤9%

Toxic concentration: ≥20%

Day(s) and Time(s) Performed

Monday through Saturday; 12 a.m.

Test Classification

This test has been cleared, approved or is exempt by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
COHBB Carbon Monoxide, B 20563-3


Result ID Test Result Name Result LOINC Value
8649 Carbon Monoxide, B 20563-3

Clinical Information

Carbon monoxide (CO) is a colorless, odorless, tasteless gas that is a product of incomplete combustion of carbonaceous material. CO poisoning causes hypoxia because CO binds to hemoglobin with an affinity 250 times greater than that of oxygen, thus preventing delivery of oxygen to the tissues, but concentrations greater than 20% are associated with symptoms of toxicity (eg, headache, fatigue, dizziness, confusion, nausea, vomiting, increased pulse and respiratory rate). CO levels greater than 50% are potentially fatal. Common exogenous sources of carbon monoxide include cigarette smoke, gasoline engines, and improperly ventilated home heating units. Small amounts of carbon monoxide are produced endogenously in the metabolic conversion of heme to biliverdin. This endogenous production of carbon monoxide is accelerated in hemolytic anemias.


The toxic effects of carbon monoxide can be seen in levels 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.


An insidious effect of carbon monoxide poisoning is the delayed development of neuropsychiatric sequelae, which may include personality changes, motor disturbances, and memory impairment. These manifestations do not correlate with the length of exposure or with the maximum blood carboxyhemoglobin concentration.


No significant cautionary statements

Clinical Reference

1. Langman LJ, Bechtel LK, Meier BM, Holstege C: In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Sixth edition. Chapter 41: Clinical toxicology. Edited by N Rifai, AR Horvath, CT Wittwer. Elsevier; 2018. pp 832-887

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

Method Description

The ABL80 OSM CO-OX analyzer is a portable, automated analyzer that measures oximetry in whole blood. Total hemoglobin (tHb), oxygen saturation (sO2), carboxyhemoglobin (COHb), and methemoglobin (MetHb) are measured by spectrophotometry. Light passes through a cuvette containing hemolyzed blood sample. The specific wavelengths absorbed and their intensity generates an absorption spectrum used to calculate oximetry parameters.(Instruction manual: ABL80 FLEX CO-OX analyzer-OSM version, Radiometer Medical ApS, 2016)

Analytic Time

Same day/1 day

Reject Due To

Gross hemolysis OK
Gross lipemia OK
Gross icterus OK

Method Name

Carboxyhemoglobin Co-oximetry


If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.