Karyotype Test

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 an extra or missing chromosome is preventing a woman from becoming pregnant or is
    causing
    miscarriages.
  • Find out whether an extra or missing chromosome 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 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.
  • Put pressure on the site and then put on 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.

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

ByHealthwise StaffPrimary Medical Reviewer Kathleen Romito, MD - Family Medicine Martin J. Gabica, MD - Family Medicine E. Gregory Thompson, MD - Internal Medicine Adam Husney, MD - Family Medicine Specialist Medical Reviewer Siobhan M. Dolan, MD, MPH - Reproductive Genetics

Current as ofFebruary 23, 2018

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