Karyotype is a test to identify and evaluate the size, shape, and number ofchromosomes in a sample of body cells. Extra, missing, or abnormal positions of chromosome pieces can cause problems with a person's growth, development, and body functions.

Why It Is Done

Karyotyping is done to:

Determine whether the chromosomes of an adult have an abnormality that can be passed on to a child.

Determine whether a chromosome defect is preventing a woman from becoming pregnant or causing miscarriages.

Determine whether a chromosome defect is present in a fetus. Karyotyping also may be done to determine whether chromosomal problems may have caused a fetus to be stillborn.

Determine the cause of a baby's birth defects or disability. Help determine the appropriate treatment for some types of cancer. Identify the sex of a person by determining the presence of the Y chromosome. This may be done

when a newborn's sex is not clear.

How To Prepare

No special preparation is needed before having this test.

Talk to your doctor about any concerns you have about the need for the test, its risks, or how it will be done. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

Since the information obtained from karyotyping can have a profound impact on your life, you may want to see a doctor who specializes in genetics (geneticist) or a genetic counselor. This type of counselor is trained to help you understand what karyotype test results mean for you, such as your risk for having a child with an inherited (genetic) condition like Down syndrome. A genetic counselor can help you make well-informed decisions. Ask to have genetic counseling before making a decision about a karyotype test.

How It Is Done

Karyotype testing can be done using almost any cell or tissue from the body. A karyotype test usually is done on a blood sample taken from a vein. For testing during pregnancy, it may also be done on a sample of amniotic fluid or theplacenta.

Blood sample from a vein

The health professional drawing your blood will:

Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.

Clean the needle site with alcohol. Put the needle into the vein. More than one needle stick may be needed. Attach a tube to the needle to fill it with blood.

Remove the band from your arm when enough blood is collected. Apply a gauze pad or cotton ball over the needle site as the needle is removed. Apply pressure to the site and then a bandage.

Cell sample from a fetus

For this type of test, cells are collected from the fetus using amniocentesis orchorionic villus sampling. For more information about amniocentesis, see the topicAmniocentesis or Chorionic Villus Sampling.

Cell sample from bone marrow

Bone marrow aspiration may be used for a karyotype test. For more information about how this test is done, see the topic Bone Marrow Aspiration and Biopsy.

How It Feels

Blood sample from a vein

You may feel nothing at all from the needle puncture, or you may feel a brief sting or pinch as the needle goes through the skin. Some people feel a stinging pain while the needle is in the vein. But many people do not feel any pain, or have only minor discomfort, once the needle is positioned in the vein. The amount of pain you feel depends on the skill of the health professional drawing the blood, the condition of your veins, and your sensitivity to pain.

Risks

Blood sample from a vein

There is very little risk of complications from having blood drawn from a vein.

You may develop a small bruise at the puncture site. You can reduce the risk of bruising by keeping pressure on the site for several minutes after the needle is withdrawn.

In rare cases, the vein may become inflamed after the blood sample is taken. This condition is called phlebitis and is usually treated with a warm compress applied several times daily.

Continued bleeding can be a problem for people with bleeding disorders.Aspirin, warfarin (Coumadin), and other blood-thinning medicines can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your health professional before your blood is drawn.

Results

Karyotype is a test to identify and evaluate the size, shape, and number ofchromosomes in a sample of body cells.

Results of a karyotype test are usually available within 1 to 2 weeks.

Karyotype

Normal: There are 46 chromosomes that can be grouped as 22 matching pairs and 1 pair of sex chromosomes (XX for a female and XY for a male).

The size, shape, and structure are normal for each chromosome.

Abnormal: There are more than or less than 46 chromosomes. The shape or size of one or more chromosomes is abnormal. A chromosome pair may be broken or incorrectly separated.

What Affects the Test

If you are being treated for cancer, the results of a karyotype test may not be accurate. Chromosomes may be damaged by some types of cancer treatment.

What To Think About

Sometimes a karyotype test is combined with other genetic tests to provide more specific information about genetic problems. For more information, see the topic Genetic Test.

If the results of karyotype are abnormal, other family members may be advised to undergo testing. A sample taken by gently swabbing the tissues inside the cheek (called a buccal swab) sometimes is

used for a karyotype test. But results from buccal swabbing are less accurate than other types of karyotype tests.

Since the information obtained from karyotyping can have a profound impact on your life, you may want to see a doctor who specializes in genetics (geneticist) or a genetic counselor. This type of counselor is trained to help you understand what karyotype test results mean for you, such as your risk for having a child with a condition like Down syndrome that is caused by a chromosome problem. A genetic counselor can help you make well-informed decisions. Ask to have genetic counseling before making a decision about a karyotype test.

References