Karyotyping Health Article

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 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