The sample is placed into a special dish or tube and allowed to grow in the laboratory. Cells are later taken from the new 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 show the arrangement of the chromosomes. This is called a karyotype.
Certain problems 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
Follow the health care provider's instructions on how to prepare for the test.
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 can:
Count the number of chromosomes
Look for structural changes in chromosomes
This test may be done:
On a couple that has a history of miscarriage
To examine any child or baby who has unusual features or developmental delays
Chemotherapy may cause chromosome breaks that affect normal karotyping results.
Risks are related to the procedure used to obtain the sample.
In some cases, a problem may occur to the cells growing in the lab dish. Karyotype tests should be repeated to confirm that an abnormal chromosome problem is actually in the body of the person.
Bacino CA. Cytogenetics. In: Kliegman RM, Stanton BF, St. Geme J III, Schor N, Behrman RE, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 76.
Chad Haldeman-Englert, MD, FACMG, Wake Forest 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, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.