Evidence quality
Surrogate marker
A measurement used as a stand-in for a direct patient-important outcome.
What it means
Definition
Surrogate marker. A surrogate marker can be useful when direct outcomes take years to measure. The risk is that improving the marker may not improve how people feel, function or survive.
What it can tell you
It can distinguish indirect biological signals from outcomes that matter directly to patients.
What it cannot tell you
It cannot assume a marker change will translate into symptom, function or survival benefit.
Headline trap
Why this matters in headlines
Lowering a blood-test value does not automatically prove fewer admissions or longer life.