A blood sample is drawn and sent to a genetics laboratory for DNA analysis. Certain locations on the DNA chain are examined for mutations that are known to be linked to specific genetic conditions in defined populations. Carrier screening for genetic diseases can also be done by means of a saliva test. However, whether the sample taken is blood or saliva, an enzyme test, which does require a blood sample, is highly recommended as the most reliable screening for Tay-Sachs disease, which is one of the most serious of the diseases on the panel.
After several weeks, a report is available which shows whether or not the individual has the mutations linked to particular diseases in a given population. The report should be carefully read by a knowledgeable doctor or trained genetic counselor.
A screening report is not a simple yes/no situation. It will tell the doctor or genetics specialist what the chances are that the patient is a carrier of a particular disease based on the mutations tested for, but there is always a residual risk that the patient has an unidentified mutation and may still be a carrier.
For more information on the screening process, watch the video A Genetic Counselor on Screening