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Medical Tests

Blood Test: Hemoglobin

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What It Is

Hemoglobin is a protein in red blood cells that transports oxygen throughout the body. A hemoglobin test is used to determine how much hemoglobin is in the blood.

Why It's Done

The hemoglobin test may be performed as part of a routine health exam or during a time of illness, but it's often done as part of a complete blood count (CBC). The hemoglobin test is primarily used to detect various types of anemia, a common condition that occurs when the amount of healthy red blood cells a person's blood is too low.

Preparation

No special preparation is necessary. However, if your child has had a transfusion in the last 3 months, or if he or she smoked just prior to the test, hemoglobin levels may be altered, so let the doctor know.

On the day of the test, it may help to have your child wear a short-sleeve shirt to allow easier access for the technician who will be drawing the blood.

The Procedure

A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band (tourniquet) is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.

After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.

drawing_blood

heel_prick_illustration

What to Expect

Either method (heel or vein withdrawal) of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.

Getting the Results

Hemoglobin samples are usually analyzed in a lab with a machine that measures the intensity of hemoglobin's red color to determine how much of it is present in the blood. Hemoglobin test results are usually available after a few hours or the next day.

Risks

The hemoglobin test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn:

  • fainting or feeling lightheaded
  • hematoma (blood accumulating under the skin causing a lump or bruise)
  • pain associated with multiple punctures to locate a vein

Helping Your Child

Having a blood test is relatively painless. Still, many children are afraid of needles. Explaining the test in terms your child might understand can help ease some of the fear.

Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.

If You Have Questions

If you have questions about the hemoglobin test, speak with your doctor.

Reviewed by: Steven Dowshen, MD
Date reviewed: February 2011

License

Note: All information is for educational purposes only. For specific medical advice, diagnoses and treatment, consult your doctor.

© 1995–2014 The Nemours Foundation/KidsHealth. All rights reserved.

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