Reasons, Procedure & Understanding The Results of a Carboxyhemoglobin Blood Test

Submitted on March 27, 2012

What is Carboxyhaemoglobin?

Carboxyhemoglobin is a complex compound formed when carbon monoxide reacts with the hemoglobin in the blood cells. The delivery of oxygen is drastically constrained when this reaction occurs. Carboxyhemoglobin blood is formed when a person inhales large quantities of carbon monoxide. When carbon monoxide is inhaled in small quantities, there is not much damage but as the amount of inhaled carbon monoxide increases, the toxicity also increases, and the person suffers from carbon monoxide poisoning.

Carbon monoxide gets emitted as a common byproduct, by all appliances that run on fuel. Large quantities of this gas are also found in oil furnaces and smoke. Heaters, refrigerators and dryers also cause emission of carbon monoxide as a byproduct. The gas emissions can be inhaled by anyone, at anytime. For unborn babies, young children and senior citizens, the emissions may be especially threatening.

Symptoms of Carbon Monoxide Poisoning

Since the body contains many hydrocarbons and carbon compounds, the presence of carbon monoxide is not easily detected. Carbon monoxide poisoning has several symptoms, all of which imitate symptoms of flu because of which the condition becomes even harder to detect. However, if you have had dizzy spells and other people around you are also experiencing similar symptoms, blood carboxyhemoglobin toxicity may not be ruled out.

Reasons Why a Carboxyhemoglobin Blood Test is Conducted

A carboxyhemoglobin blood test may be done for several reasons. These tests are usually not performed as routine tests or health screenings. They are usually ordered when carbon monoxide poisoning is suspected. If a person has some other medical conditions, a laboratory test can help determine if the condition of the person is improving or worsening. People who are taking medications for carbon monoxide poisoning may be asked to take regular tests in order to monitor the treatment.


The carboxyhemoglobin test is performed on a blood sample collected from a vein or an artery. The blood is examined to find out traces of carboxyhemoglobin in it. The total time taken to perform the test is usually 24 hours but it may differ from laboratory to laboratory.

Interpretation of Test Results

The results of the test depend largely on the age, medical history, gender, and the specific method used for the test. Whether the blood is drawn from an artery or a vein also affects the test results. The normal results of the test are when the carboxyhemoglobin is less than 2.3% in adults. For adults who smoke, the normal values range between 2.1%-4.2% and for those who smoke heavily, normal results range from 8%-9%.