Evidence-appraisal glossary
Surrogate endpoint
A surrogate endpoint is a substitute measure, such as a lab value or scan finding, used to stand in for an outcome that matters directly to patients, like survival or symptoms. It is easier or faster to measure but does not always predict the real outcome.
Also called: surrogate marker, surrogate outcome, intermediate endpoint.
A surrogate endpoint is a laboratory marker, imaging result, or other intermediate measure used in place of a clinically important outcome such as death, heart attack, or quality of life. Surrogates can make trials shorter and cheaper because they change sooner than hard outcomes. The danger is that improving a surrogate does not guarantee improving the outcome patients care about, and a treatment can move the marker in the right direction while leaving real outcomes unchanged or worse. When reading a study, ask whether the primary endpoint is something patients feel or care about or merely a stand-in, and whether that surrogate has been validated as predicting the real outcome for this kind of treatment. A well-known cautionary example: some drugs suppressed abnormal heart rhythms, a surrogate, yet later trials found they increased deaths. Treat surrogate-based claims as provisional until hard-outcome data confirm the benefit.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.