Karyotyping is a test using a microscope to identify chromosome abnormalities from malformation or disease. It examines the size, shape, and number of chromosomes in a certain sample of cells. Extra, missing, or abnormal positions of chromosome pieces can cause problems with a person’s growth, development, and body functions.
What is it used for?
A karyotype test may be used to:
- Check an unborn baby for genetic disorders
- Diagnose a genetic disease in a baby or young child
- Find out if a chromosomal defect is preventing a woman from getting pregnant or is causing miscarriages
- Check a stillborn baby (a baby that died late in pregnancy or during birth) to see if a chromosomal defect was the cause of death
- See if you have a genetic disorder that could be passed along to your children
- Diagnose or make a treatment plan for certain types of cancer and blood disorders
What Do Karyotype Tests Look For?
Karyotype tests study your baby’s chromosomes to see if they are normal or not. Humans have 46 chromosomes (23 pairs). Babies inherit 23 from their mom and 23 from their dad.
Sometimes, babies have an extra chromosome, a missing chromosome, or an abnormal chromosome. Karyotype tests will determine if any of these have happened with your baby. The most common things that doctors look for with karyotype tests include:
Down syndrome (trisomy 21) A baby has an extra, or third, chromosome 21. This affects how the baby looks and learns.
Edwards’s syndrome (trisomy 18) A baby has an extra 18th chromosome. Babies usually have many problems, and most don’t survive more than a year.
Patau syndrome (trisomy 13) A baby has an extra 13th chromosome. Babies usually have heart problems and severe mental impairment. Most won’t live for more than a year.
Klinefelter syndrome A boy baby has an extra X chromosome (XXY). He may go through puberty at a slower pace, and he may not be able to have his own children.
Turner syndrome A girl baby has a missing or damaged X chromosome. It causes heart problems, neck problems, and short height.
The test can be performed on almost any tissue, including:
- Amniotic fluid
- Bone marrow
- Tissue from the organ that develops during pregnancy to feed a growing baby (placenta)
- To test amniotic fluid, an amniocentesis is done.
The 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. 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.
Specimen type: Whole blood
Preferred collection container: 10 ml green/green-top (sodium heparin) tube
Specimen required: 3-5 ml whole blood; minimum 1 ml.
Special notes: Clinical history and reason for referral are required with test order.
Specimen processing instructions: Do not centrifuge or refrigerate.
Transport temperature: Room temperature.
Rejection criteria: Frozen specimens unacceptable.