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.

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

A health professional uses a needle to take a blood sample, usually from an arm.

Cell sample from a fetus

For this type of test, cells are collected from the fetus using amniocentesis or chorionic villus sampling.

Cell sample from bone marrow

Bone marrow aspiration may be used for a karyotype test.

Watch

How It Feels

Karyotype testing is usually done using a blood sample from a vein. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

Blood sample from a vein

There is very little chance of having a problem from this test. A small bruise may form at the site.

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.

Credits

Current as of: July 17, 2020

Author: Healthwise Staff
Medical Review:
Kathleen Romito MD - Family Medicine
Martin J. Gabica MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Siobhan M. Dolan MD, MPH - Reproductive Genetics

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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. Learn how we develop our content.