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:
The test can be performed on almost any tissue, including:
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.
There is no special preparation needed.
How the test will feel depends on whether the sample procedure is having blood drawn (venipuncture), amniocentesis, or bone marrow biopsy.
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.
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:
The risks are related to the procedure used to obtain the specimen.
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.
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: