How does cell-free DNA screening differ from diagnostic testing?

Cell-free DNA screening is a prenatal test that analyzes small fragments of fetal DNA circulating in a pregnant person's blood. This form of testing is primarily designed to assess the risk of certain genetic conditions, such as Down syndrome, rather than providing a definitive diagnosis.

The key characteristic of cell-free DNA screening is its high sensitivity, meaning that it can effectively identify a significant proportion of pregnancies at risk for these conditions. However, because it is a screening tool and not a diagnostic tool, it does not provide conclusive results. A positive result suggests an increased risk, prompting further diagnostic testing, such as chorionic villus sampling (CVS) or amniocentesis, to confirm the presence of any genetic abnormalities.

In contrast, diagnostic tests offer conclusive answers about the presence or absence of genetic conditions. They typically involve more invasive procedures to obtain samples directly from the fetus. Screening tests like cell-free DNA are beneficial due to their non-invasive nature and the relative safety for both the mother and the fetus, but they are not definitive and should always be followed up with diagnostic testing if required.

Thus, the essential distinction lies in the nature of the results provided by cell-free DNA screening—it identifies risk without confirming a diagnosis.