Use of test
Abnormalities of chromosome number can cause spontaneous miscarriage, or the birth of a baby with congenital malformations and developmental delay. This is a rapid test of the numbers of selected chromosomes in a sample of the placenta, amniotic fluid, or fetal blood. It is then followed by a diagnostic chromosome analysis by karyotype or microarray. This test provides diagnostic and prognostic information. The standard set of tested chromosomes are 13, 18, 21, X and Y. Other FISH probes can be added on specific request (e.g. 22q11.2).
An abnormal result provides a genetic diagnosis and the basis for genetic counselling. A normal result does not exclude a genetic or heritable disorder.
This is an assay for mutations which may be heritable or de novo. It may raise issues of ethics or consent that are different from most other investigations ordered in the routine care of a patient.
Analysis of the number of selected chromosomes by fluorescent in situ hybridisation (FISH).
Requesting the test
This test is usually requested by an obstetrician or clinical geneticist.
Chorionic villus sample, amniotic fluid, or fetal blood sample are required. An invasive procedure by an obstetrician is necessary to obtain this.
To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.
We recommend that the patient or another adult check the labelling of request forms and sample tubes.
Please include details of any clinical abnormalities in the patient being tested, and the results of chromosome studies in relatives.
1-2 business days for targeted FISH, 15 business days for chromosome studies.
This investigation is provided at no cost for patients having cytogenetic studies of CVS or amniotic fluid following a "high risk" result for the Harmony test through Sonic Genetics.
This test is not rebated by Medicare. The laboratory assumes that the patient or client has provided informed financial consent for the test.