Kariotype: procedures, processes, and how to read the results

Definition

What is a karyotype?

A karyotype is a test to identify and assess the size, shape and number of chromosomes in a sample of body cells. Additional or missing chromosomes, or the abnormal position of parts of the chromosomes, can cause problems with a person's growth, development, and function.

When do I need a karyotype?

This test may be done:

in couples who have a history of miscarriage
to check for a child or infant who has unusual features or delayed development

Blood or bone marrow tests can be done to identify the Philadelphia chromosome, which is found in 85% of people with chronic myelogenous leukemia (CML). An amniotic fluid test is done to check the developing baby for chromosome problems.

Precautions & warnings

What should I know before undergoing a karyotype?

Since the sex chromosome (XX or XY) is identified during chromosome analysis, this test will also determine the sex of the fetus. Some chromosomal changes are too small or subtle to be detected by a karyotype. Several other test techniques of sorts fluorescent in situ hybridization (FISH) or microarray may sometimes be used to further investigate chromosomal abnormalities. People may have cells in the body with different genetic material. This occurs because of early changes in fetal development that result in specific differences in cell lines and are called mosaics. Examples are some cases of Down syndrome. Affected people may have some cells with an additional third chromosome 21 and some cells with normal pairs.

Process

What should I do before undergoing a karyotype?

You don't need to do anything before undergoing this test. Talk to your doctor about what the test entails, the risks, or the test procedures that will be performed. Since the information you get from a karyotype can have a big impact on your life, you may want to see a genetic specialist (genetysis) or a genetic counselor. This type of counselor is trained to help you understand what the karyotype test results mean to you, such as the risk of having a child with an inherited (genetic) condition such as Down's syndrome. A genetic counselor can help you make an informed decision. Ask for genetic counseling before making a decision about a karyotype.

How is the karyotype test process?

Blood sample from an artery

The healthcare professional who draws blood will:

wrap an elastic belt around your upper arm to stop blood flow. This makes the blood vessel under the bundle enlarge making it easier to insert the needle into the vessel
clean the area to be injected with alcohol
inject a needle into a vein. More than one needle may be required.
Insert the tube into the syringe to fill it with blood
untie the knot from your arm when enough blood is drawn
sticking gauze or cotton on the injection site, after the injection is complete
apply pressure to the area and then put a bandage on

Cell samples from the fetus

For this type of test, cells are collected from the fetus using an amniocentesis or chorionic villus sample.

Cell sample from bone marrow

Bone marrow aspiration may be used for a karyotype.

What should I do after a karyotype?

An elastic band is wrapped around your upper arm and will feel tight. You may not feel anything when you get the injection, or you may feel like you are stung or pinched. You can remove the bandage and cotton in 20-30 minutes. You will be notified when you can get the test results. The doctor will explain what your test results mean. You must follow the doctor's instructions.