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Karyotyping

Definition

Karyotyping is a test to examine chromosomes in a sample of cells, which can help identify genetic problems as the cause of a disorder or disease. This test can:

  • Count the number of chromosomes
  • Look for structural changes in chromosomes

Alternative Names

Chromosome analysis

How the test is performed

The test can be performed on almost any tissue, including:

  • Amniotic fluid
  • Blood
  • Bone marrow
  • Tissue from the organ that develops during pregnancy to feed a growing baby (placenta)

To test amniotic fluid, an amniocentesis is done.

A bone marrow specimen requires a bone marrow biopsy.

The sample is placed into a special dish and allowed to grow in the laboratory. Cells are later taken from the growing sample and stained. The laboratory specialist uses a microscope to examine the size, shape, and number of chromosomes in the cell sample. The stained sample is photographed to provide a karyotype, which shows the arrangement of the chromosomes.

Certain abnormalities can be identified through the number or arrangement of the chromosomes. Chromosomes contain thousands of genes that are stored in DNA, the basic genetic material.

How to prepare for the test

There is no special preparation needed.

How the test will feel

How the test will feel depends on whether the sample procedure is having blood drawn (venipuncture), amniocentesis, or bone marrow biopsy.

Why the test is performed

This test is usually done to evaluate a couple with a history of miscarriages, or to examine any child or baby who has unusual features or developmental delays that suggest a genetic abnormality.

The bone marrow or blood test can be done to identify the Philadelphia chromosome, which is found in about 85% of people with chronic myelogenous leukemia (CML).

The amniotic fluid test is done to check a developing fetus for chromosome abnormalities.

Normal Values

  • Females: 44 autosomes and 2 sex chromosomes (XX), written as 46, XX
  • Males: 44 autosomes and 2 sex chromosomes (XY), written as 46, XY

What abnormal results mean

Abnormal results may be due to a genetic syndrome or condition, such as:

This list is not all-inclusive.

Additional conditions under which the test may be performed:

What the risks are

The risks are related to the procedure used to obtain the specimen.

See:

In some cases, an abnormality may occur as the cells as growing in the lab dish. Karyotype tests should be repeated to confirm that an abnormal chromosome problem is actually in the body of the patient.

Special considerations

Chemotherapy may cause chromosome breaks that affect normal karotyping results.

See also: Mosaicism

Your doctor may also order other tests that go together with a karyotype:

  • Telomere studies -- look at the ends of the chromosomes
  • Microarray -- looks at small changes in the chromosomes
  • Fluorescent in situ hybridisation (FISH) -- looks for small mistakes such as deletions in the chromosomes

Review Date: 12/1/2010
Reviewed By: Chad Haldeman-Englert, MD, Wake Forest University School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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