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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.

WebMD Medical Reference from Healthwise

Last Updated: March 12, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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