Medical Tests |
 |
 |
A B C D E F G H I J K L M N O P Q R S T U V W X All Medical Tests
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 a sample of blood, bone marrow, amniotic fluid, or tissue from the placenta, the organ that develops during pregnancy to feed a growing baby.
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 venipuncture (having blood drawn), 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 an abnormal appearance of the body that suggests a genetic abnormality.
The bone marrow or blood test can be done to identify the Philadelphia chromosome, which is found in about 85% of those 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), denoted 46, XX
- Males: 44 autosomes and 2 sex chromosomes (XY), denoted 46, XY
What abnormal results mean
Abnormal results may be due to:
- Down syndrome
- Klinefelter syndrome
- Philadelphia chromosome
- Trisomy 18
- Turner syndrome
This list is not all-inclusive.
Additional conditions under which the test may be performed:
- Chronic myelogenous leukemia (CML) or other leukemias
- Multiple birth defects
- Ambiguous genitalia
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: Mosaicism
Your doctor may also order a test called telomeres that looks at the ends of the chromosomes. It is often ordered along with the karyotyping test.
Review Date: 6/24/2007
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician 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. Copyright ©2003 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.
Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Medical Center. Please discuss with your doctor any questions or concerns you may have.
|
