Genetic screening and genetic testing are two distinct procedures in medical genetics, though the terms are frequently used interchangeably. This common confusion can obscure the fundamental differences in their purpose, the populations they target, and the clinical meaning of their results. Both procedures analyze an individual’s DNA, RNA, chromosomes, proteins, or metabolites for clinical purposes, but they serve entirely different functions.
Genetic Screening: Population Focus and Risk Assessment
Genetic screening is applied to a large, unselected population or a specific subgroup who are generally healthy and show no symptoms of a genetic disorder. The primary purpose of screening is to identify individuals who have an elevated statistical risk for a condition or who are carriers of a recessive genetic change. Screening is not a diagnostic tool but rather a method for flagging those who may require further, more definitive investigation.
The results of a screening procedure provide a probability or risk score rather than a definitive medical diagnosis. For instance, newborn screening (NBS) is universally performed shortly after birth to assess the risk for over 35 treatable genetic conditions, such as phenylketonuria. Carrier screening is another common example, where prospective parents without a family history may be screened for genetic variants that cause Cystic Fibrosis or Tay-Sachs disease.
Genetic Testing: Individual Focus and Diagnostic Confirmation
Genetic testing, in contrast, is a targeted procedure applied to an individual who is already suspected of having a genetic condition. This individual may be showing specific symptoms, have a known family history of a disorder, or have received a positive result from a previous screening procedure. The goal of testing is to confirm or rule out a suspected genetic diagnosis, provide a prognosis, or guide treatment options.
Diagnostic testing is used to confirm conditions like Huntington’s disease or Muscular Dystrophy in a person exhibiting symptoms. Predictive testing is another form, used in asymptomatic individuals with a strong family history to determine if they possess an adult-onset genetic change, such as BRCA1/2 mutations that confer an increased risk for certain cancers. A specialized application is pharmacogenomic testing, which analyzes specific genetic variants to predict how an individual will metabolize and respond to particular medications, allowing for personalized drug selection and dosage.
Interpreting Results: Understanding Outcomes and Next Steps
The interpretation of results and the subsequent medical actions represent the most significant distinction between screening and testing. When a screening procedure indicates an increased risk, it is referred to as a “positive screen,” and this result is not conclusive evidence of a disorder. Because screening procedures are designed to be highly sensitive to avoid missing anyone at risk, they inherently have a greater potential for false positives, meaning the result suggests a risk that does not actually exist. The next step following a positive screen is nearly always a recommendation for a more definitive diagnostic genetic test, often coordinated with a genetic counselor. This follow-up testing moves from a general risk assessment to a highly detailed analysis, such as gene sequencing, to confirm the presence or absence of the specific pathogenic variant.
Conversely, a positive result from a diagnostic genetic test is generally considered definitive, providing a confirmed diagnosis or highly certain risk prediction. The medical actions that follow a positive test are direct and focused, involving the immediate development of treatment plans, enhanced surveillance protocols, or discussions about prognosis and lifestyle adjustments. However, even diagnostic results can be complex; a finding might be categorized as a Variant of Uncertain Significance (VUS), meaning the laboratory found a genetic change whose connection to a disease is not yet fully understood.