Biomarker

What is a biomarker?

A biomarker, short for biological marker, is a measured biological characteristic used to indicate a biological process, disease process, or response to an exposure or treatment. Examples include blood glucose, blood pressure, and particular proteins measured in blood or tissue.

A biomarker's meaning depends on its intended use. A measurement useful for monitoring an established disease is not automatically suitable for screening healthy people, choosing treatment, or predicting an individual's outcome.

Examples of biomarkers

• Blood glucose: a measurement used in assessing and monitoring glucose regulation, including diabetes.
• Amyloid-beta and tau: measurements of these proteins are used in Alzheimer’s research and assessment. The National Institute on Aging explains how cerebrospinal-fluid measures and brain imaging can provide evidence about disease-related changes.
• Prostate-specific antigen (PSA): a blood measurement relevant to prostate conditions. The National Cancer Institute notes that both cancer and benign conditions can raise it. A raised value is not, by itself, a cancer diagnosis.

Biomarkers and clinical outcomes

Changing a biomarker does not necessarily mean that a treatment helps people feel better, function better, or live longer. Using a biomarker as a substitute for a clinical outcome requires additional evidence for that specific use. The FDA explains this distinction in Biomarkers and Surrogate Endpoints.