Karyotyping

• 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:

  • 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
• What the risks are

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

  See:

  • Amniocentesis
  • Bone marrow biopsy
  • Chorionic villus sampling
  • Venipuncture

  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: 2/20/2009

Reviewed By: Diana Chambers, MS, EdD, Certified Genetics Counselor (ABMG), Charter Member of the ABGC, University of Tennessee, Memphis, TN. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.