A prognostic test is a type of medical test that predicts a patients likelihood of developing a disease or experiencing a medical event. Unlike diagnostic tests, which diagnose specific diseases and conditions, prognostic tests predict the likely progress of a disease, such as the likelihood of experiencing repeated flares or the likelihood of developing complications. Prognostic markers, also known as biomarkers, are characteristics that help to identify or categorize people with different risks of specific future outcomes. Prognostic tests can be used to estimate the severity of a disease and help inform treatment-decision making. In some contexts, prognostic tests can also be used to predict beneficial or adverse responses to a treatment, and these are commonly known as predictive tests. Prognostic tests are often incorporated into multivariable regression models or algorithms for analysis.