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Karyotype Test

Test Overview

Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells. Extra or missing chromosomes, 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:

  • Find out whether the chromosomes of an adult have a change that can be passed on to a child.
  • Find out whether a chromosome defect is preventing a woman from becoming pregnant or is causing miscarriages.
  • Find out whether a chromosome defect is present in a fetus. Karyotyping also may be done to find out whether chromosomal problems may have caused a fetus to be stillborn.
  • Find out 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 checking for the presence of the Y chromosome. This may be done when a newborn's sex is not clear.

How To Prepare

You do not need to do anything before you have 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 formmedical 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 the placenta.

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 or chorionic villus sampling.

For more information about amniocentesis, see:

Cell sample from bone marrow

Bone marrow aspiration may be used for a karyotype test. To learn more 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 chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the puncture site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This condition is called phlebitis. You can use a warm compress several times daily to treat this.
  • Ongoing bleeding can be a problem for people who have bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes 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 fewer 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

  • If the results of karyotype are abnormal, other family members may be advised to have the test.
  • 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.
  • Sometimes a karyotype test is combined with other genetic tests to provide more specific information about genetic problems. To learn more, see the topic Genetic Test.

References

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
  • Skirton H, Patch C (2009). Genetics for the Health Sciences: A Handbook for Clinical Healthcare, 2nd ed. Oxfordshire, UK: Scion Publishing.

Credits

By Healthwise Staff
Kathleen Romito, MD - Family Medicine
Siobhan M. Dolan, MD, MPH - Reproductive Genetics
Last Revised November 29, 2012

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

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