Karyotyping, or chromosome analysis, checks the number and structure of a person's chromosomes to detect abnormalities such as Down syndrome (Trisomy 21).
Karyotyping is the gold-standard test to rule out chromosome abnormalities. It also identifies structural changes such as balanced translocations and confirms the exact chromosome count (ploidy level).
Genetics explained
46Chromosomes in a normal human cell
23Pairs: 22 autosomes + 1 sex chromosome pair
XX / XYFemale / male sex chromosomes
Chromosomes are thread-like structures inside the cell nucleus that carry our genes. Genes influence inherited traits, growth, development and body function through the proteins they produce.
Most body cells contain a full set of chromosomes. Eggs and sperm carry half a set, and at conception the two halves combine to form 46 chromosomes in the developing baby.
When is a karyotype test requested?
- To find the cause of a baby's congenital (present-at-birth) physical abnormalities, such as Down syndrome.
- To check an unborn baby when chromosomal problems such as Down, Patau or Edwards syndrome are suspected.
- For couples with recurrent pregnancy loss, to identify balanced translocation carriers and plan future pregnancies.
- For couples undergoing infertility treatment or PGT-A, when Klinefelter syndrome (47,XXY), Turner syndrome (45,X) or a family history of chromosome abnormalities is suspected.
- For men with abnormal semen parameters, particularly oligospermia or severe oligozoospermia (below 10 million/ml).
- To confirm sex chromosome abnormalities in cases of ambiguous genitalia or discordant sex.
- To diagnose and manage blood cancers caused by acquired chromosome changes, such as chronic myeloid leukaemia (CML).
Test types & sample requirements
| Test | Purpose | Sample | Container | Volume |
|---|---|---|---|---|
| Single blood lymphocyte culture | Detect chromosome abnormalities in adults or children | Peripheral blood | Sodium heparin (green top) | 4 ml |
| Couple blood lymphocyte culture | Husband & wife with recurrent pregnancy loss | Peripheral blood (each partner) | Sodium heparin (green top) | 4 ml each |
| Prenatal karyotyping | Detect abnormalities during pregnancy, incl. Down syndrome | Amniotic fluid / CVS in transport media | Falcon tube, sterile container | 20 ml |
| Products of conception (POC) | After pregnancy loss, spontaneous abortion or miscarriage | Placental / fetal tissue in normal saline | Sterile container | — |
| Postnatal karyotyping | Detect chromosome abnormalities in adults or children | Peripheral blood / bone marrow aspirate | Sodium heparin (green top) | 4 ml |
| Haematologic malignancy karyotyping | Guide diagnosis & treatment in blood cancers | Peripheral blood / bone marrow aspirate | Sodium heparin (green top) | 3 ml |