Genetic screening is a testing procedure applied either to a large population of individuals (newborn infants, for instance) or to an individual or family thought to be at risk of a particular condition, to look for indications of a genetic disease. A genetic disease is a condition that is passed down from a parent to his or her offspring.
Who is a candidate for the test?
Some genetic screening, such as phenylketonuria (PKU) testing, is done on all newborn babies in this country. PKU, for instance, can be prevented if it is identified early in the child's life. In addition, genetic screening is often done on people from certain ethnic groups. Individuals of Eastern Europen Jewish descent, for example, are often screened for Tay-Sachs disease.
People who have relatives with genetic disease may seek genetic screening to determine if they are at risk for developing the condition as well. They also might want to know whether they can pass it on to their children.
How is the test performed?
Genetic screening is not always a sophisticated test. It may involve looking for certain chemicals in blood or urine. It also may involve DNA testing or chromosome analysis. Usually, a sample of blood or urine is collected and sent to a laboratory for analysis.
Simple tests are done in many laboratories around the country. Newborn population screening is often done in a public health laboratory, using a needleprick sample of the newborn's blood blotted onto filter paper. Sophisticated DNA tests and chromosome analysis are done in genetics laboratories.
What is involved in preparation for the test?
Screening for some compounds in the blood or urine may require fasting or a special diet before the test. DNA tests and chromosome analysis do not require preparation. A person should consult the healthcare professional for specific instructions.
What do the test results mean?
If certain compounds are found in the blood or urine, the screening test is said to be positive. This means that there is reason to believe that a genetic disease may be present. The tests are designed to be as sensitive as possible so as not to miss cases, but there are many false positives. Therefore, a more refined test is used to distinguish those who actually have the condition.
If the refined test, such as a DNA test, is positive, the genetic disease is present and treatment is started. Genetic counseling may be appropriate. Chromosome analysis is also accurate. If the results are positive, there is a risk to pass on a genetic disease and action is taken.
Kelly TE: Clinical Genetics and Genetic Counseling. Year Book Medical Publishers, 1980.