What It Is
A karyotype test is a laboratory test that examines a person's chromosomes, the structures within cells that carry genetic material, to check their number and overall structure.
What It Checks
A karyotype test arranges and examines all of a person's chromosomes under a microscope, checking whether the expected number is present and whether any chromosomes show structural abnormalities, such as missing or extra material, or unusual rearrangements.
Why It's Used
A karyotype test is commonly used to investigate suspected chromosomal conditions, evaluate certain cases of infertility or recurrent pregnancy loss, and, during pregnancy, to analyze samples obtained through procedures like amniocentesis or CVS when a chromosomal condition is suspected.
How It's Done
A karyotype test requires a sample of cells, which can come from a blood sample in most cases, or from other sources such as amniotic fluid during pregnancy. In the laboratory, the cells are grown for a period of time, then treated to capture chromosomes at a specific stage where they're most visible, stained, and examined under a microscope, with images of the chromosomes arranged and analyzed for the final result.
Background
The correct number of human chromosomes was only definitively established in the late 1950s, a discovery that opened the door to karyotype testing as a diagnostic tool. Techniques for preparing and analyzing chromosomes were refined considerably over the following decades, including the development of staining methods that made individual chromosomes and their structure easier to distinguish, and karyotype testing remains a foundational technique in genetic diagnosis today.