Karyotyping
Alternative Names: Chromosome analysis
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
Why is the Test 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.
How is the Test 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.
Preparation for the Test
There is no special preparation needed.
How will the Test Feel?
How the test will feel depends on whether the sample procedure is having blood drawn (venipuncture), amniocentesis, or bone marrow biopsy.
Karyotyping Risks
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.
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
Normal Results for Karyotyping
- 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:
- 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:
- Ambiguous genitalia
- Chronic myelogenous leukemia (CML) or other leukemias
- Developmental delays
- Multiple birth defects
Related Images
Learn more about Karyotyping
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.
Copyright 2011 A.D.A.M., Inc.
