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Hemoglobin derivatives

Definition

Hemoglobin derivatives are altered forms of hemoglobin, a protein in red blood cells that moves oxygen and carbon dioxide between the lungs and body tissues.

This article discusses the test used to detect and measure the amount of hemoglobin derivatives in your blood.

Alternative Names

Methemoglobin; Carboxyhemoglobin; Sulfhemoglobin

How the test is performed

The test is performed using a small needle to collect a sample of blood from an artery. The sample may be collected from an artery in the wrist, groin, or arm.

Before blood is drawn, the health care provider may test circulation to the hand (if the wrist is the site). After the blood is drawn, pressure applied to the puncture site for a few minutes stops the bleeding.

See also: Blood gases

How to prepare for the test

No special preparation is needed.

If your child is going to have this test, it may help to explain how the test will feel, and even demonstrate on a doll. Explain the reason for the test. Knowing the "how and why" may reduce the anxiety your child feels.

How the test will feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

This test is used to diagnose carbon monoxide poisoning and other changes in hemoglobin that may result from certain drugs. If certain chemicals or drugs get into the blood stream, they can change the hemoglobin so it no longer works properly.

For example, carboxyhemoglobin is an abnormal form of hemoglobin that attaches to carbon monoxide instead of oxygen or carbon dioxide. High amounts of this type of abnormal hemoglobin prevent the normal movement of oxygen by the blood.

Sulfhemoglobin is a rare abnormal form of hemoglobin that cannot carry oxygen. It may result from certain medicines such as phenacetin or sulfonamides.

Methemoglobin occurs when the iron that is part of hemoglobin is changed so that it does not carry oxygen well. Certain compounds introduced into the blood stream can cause this problem:

• Sulfonamides
• Chlorates
• Nitrates
• Nitrites
• Aniline
• Phenacetin

See also: Methemoglobinemia

Normal Values

The following values represent the percentage of hemoglobin derivatives based on total hemoglobin:

• Carboxyhemoglobin: less than 3% (but may be as high as 15% in smokers)
• Methemoglobin: less than 3%
• Sulfhemoglobin: undetectable

What abnormal results mean

High levels of hemoglobin derivatives can lead to significant health problems. The altered forms of hemoglobin do not allow oxygen to be moved properly through the body. This can lead to tissue death.

The following values, except sulfhemoglobin, represent the percentage of hemoglobin derivatives based on total hemoglobin:

Carboxyhemoglobin:

• 10 - 20% symptoms of carbon monoxide poisoning begin to appear
• 30% severe carbon monoxide poisoning present
• 50-80% results in deadly carbon monoxide poisoning

Methemoglobin:

• 10-25% results in cyanosis
• 35-40% results in shortness of breath and headache
• Over 60% results in lethargy and stupor
• Over 70% results in death

Sulfhemoglobin:

• Values of 10 grams per deciliter (gm/dL) cause bluish skin color due to lack of oxygen (cyanosis), but do not cause harmful effects

What the risks are

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Christiani DC. Physical and chemical injuries of the lung. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 94.

Nagel RL. Methemoglobinemias and unstable hemoglobins. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 168.