MedlinePlus Medical Encyclopedia: Hemoglobin derivatives

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Hemoglobin derivatives

Contents of this page:
Illustrations Alternative names Definition How the test is performed How to prepare for the test How the test will feel	Why the test is performed Normal Values What abnormal results mean What the risks are Special considerations

Illustrations

Blood test

Alternative names Return to top

Methemoglobin; Carboxyhemoglobin; Sulfhemoglobin; Carbon monoxide poisoning

Definition Return to top

This is a blood test to detect and measure the percentage of abnormal hemoglobin derivatives that result from drugs such as nitroglycerin or poisoning by carbon monoxide.

How the test is performed Return to top

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

The samples are then sent to the lab where the percentage of total hemoglobin vs. derivatives is evaluated.

How to prepare for the test Return to top

If your child is to have this test performed it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.

How the test will feel Return to top

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

Why the test is performed Return to top

Hemoglobin is the substance in red blood cells that transports oxygen and carbon dioxide between the lungs and body tissues.

If certain chemicals or drugs are introduced into the blood stream, they can alter the hemoglobin so it no longer functions as a transport medium. Measuring abnormal hemoglobins can be helpful in diagnosing and monitoring exposure to these agents.

Carboxyhemoglobin is hemoglobin bound to carbon monoxide instead of oxygen or carbon dioxide. Carbon monoxide has a much higher affinity for hemoglobin than does oxygen (210 times more), and high percentages of carboxyhemoglobin in the blood impairs the normal transport of oxygen by the blood.

Sulfhemoglobin results from the union of hemoglobin with medications such as phenacetin or sulfonamides. This form of hemoglobin is unable to transport oxygen, and is untreatable. The only solution is to wait until the affected red blood cells are destroyed as part of their normal life cycle.

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

sulfonamides
chlorates
nitrates
nitrites
aniline
phenacetin

There is also a congenital form of this disorder caused by a deficiency of NADH cytochrome b5 reductase, and another form caused by hemoglobin M disease.

Normal Values Return to top

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

carboxyhemoglobin: 3% (but may be as high as 15% in smokers)
methemoglobin: less than 3%
sulfhemoglobin: undetectable

What abnormal results mean Return to top

As abnormally high levels of hemoglobin derivatives rise, there are increasingly detrimental effects. Since these forms of hemoglobin do not permit the transfer of oxygen, the effects on the body are related to lack of oxygen to the tissues, which can result in tissue death.

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

Carboxyhemoglobin:

20% symptoms of carbon monoxide poisoning begin to appear
30% severe carbon monoxide poisoning present
50-80% results in fatal 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 gm/dl result in cyanosis, but do not produce toxic effects

Note:

lower levels are hemoglobin derivatives produce the same effects in children.
gm/dl = grams per deciliter

What the risks are Return to top

Risks associated with having blood drawn are slight:

excessive bleeding
fainting or feeling light-headed
hematoma (blood accumulating under the skin)
infection (a slight risk any time the skin is broken)
multiple punctures to locate veins

Special considerations Return to top

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.

Update Date: 9/3/2003

Updated by: Michael C. Milone, M.D., Ph.D., Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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