What a Biomarker Is — and What It Is Not
A biomarker is a measurement that stands in for something we care about. Sometimes the stand-in holds. Often it does not.
Last reviewed September 10, 2026
A biomarker is any measurable indicator of a biological state: blood glucose, blood pressure, an inflammatory protein, a scan finding. Research relies on them because outcomes like heart attacks take years to accumulate.
Surrogate endpoints can mislead
Medicine has a long history of biomarkers moving in the desired direction while patient outcomes did not improve, and occasionally worsened. This is why regulators distinguish validated surrogates from exploratory ones.
A compound that improves a marker has produced a hypothesis about health, not a demonstration of it.
Questions worth asking
Is this marker validated as a surrogate for the outcome being claimed? Was the change large enough to be clinically meaningful, or merely statistically detectable? And was it pre-specified, or found afterwards among many measurements?