Predictive genetic testing is genetic testing offered to a person who currently has no signs or symptoms of a particular inherited condition but who is known to be at increased risk of developing it, usually because a specific disease-causing genetic change has already been identified in a relative. The purpose of the test is to determine whether that same change is also present in the at-risk individual, which can clarify future health risk before any illness has appeared.

This is a meaningfully different situation from diagnostic testing, in which a person who already has signs or symptoms undergoes genetic testing to confirm or explain those findings. Because the person undergoing predictive testing is, by definition, healthy at the time of testing, the result carries a different kind of weight: rather than confirming an existing illness, it reshapes a person’s understanding of their future.

A few related terms are sometimes used, each with a slightly different meaning:
• Predictive testing generally refers to testing for conditions where a positive result does not guarantee that the condition will develop, or where the age of onset and severity cannot be precisely predicted, such as many adult-onset conditions with reduced penetrance.
• Presymptomatic testing is sometimes used interchangeably with predictive testing, though some sources reserve it for conditions where, in a person carrying the disease-causing change, the condition is essentially certain to eventually develop, such as Huntington disease.
• Carrier testing, by contrast, identifies whether a person carries a single copy of a genetic change for a condition that only causes disease when two copies are present, and does not by itself predict that person’s own future health.

Because predictive testing can only be performed once the specific genetic change responsible for the condition in that family has already been identified through testing of an affected relative, it is not typically the first step in a family’s genetic evaluation.