Biomarkers

#A measurement with a defined role

A biomarker is a measurable characteristic that indicates something about a biological process, a disease process or a response to an exposure or treatment. Biomarkers can include substances in blood, genetic features, tissue findings and imaging measurements. Their meaning depends on the context in which they are used.

Calling something a biomarker does not establish that it is useful for every purpose. The measurement needs to be reliable, and evidence must connect it to the question being asked. A marker studied in one condition or population may have a different meaning, or no established role, elsewhere.

#Diagnostic, prognostic and predictive roles

A diagnostic biomarker helps detect or confirm a condition or identify a particular subtype. It may contribute to diagnosis without being sufficient on its own. Some markers occur in several conditions, so a detected or raised result may need interpretation alongside symptoms, examination findings and other tests.

A prognostic biomarker provides information about the likely course of a condition, such as the chance of progression. A predictive biomarker indicates differences in the likely effect of a particular treatment. These roles are distinct: indicating a poorer outlook does not automatically identify which treatment would work better.

#Monitoring and meaningful outcomes

A monitoring biomarker is measured repeatedly to assess disease status or changes during care. A change may reflect treatment effects, disease activity or another influence. Interpretation requires attention to normal fluctuation, measurement variation and the time over which the marker is expected to respond.

Biomarkers do not necessarily measure how a person feels, functions or survives. When a biomarker substitutes for a health outcome in research, strong evidence is needed that changes in it reliably reflect meaningful benefit in that setting. A promising signal is not, by itself, proof of better health outcomes.

#Common misunderstandings

A biomarker result is not automatically a diagnosis. The same measurement may be affected by several conditions, medicines or normal biological variation. A result outside a laboratory’s reference range does not always mean disease, and a result within that range does not rule out every problem.

“Predictive” also does not mean certain. A biomarker may help identify people more likely to benefit from a particular treatment, but it cannot guarantee an individual response. Likewise, a marker associated with a higher chance of illness does not show that the illness will definitely develop.

More testing is not always more useful. A test needs a clear purpose, reliable measurement and evidence that its result can inform care. Finally, improving a biomarker is not necessarily the same as improving health: a change in a laboratory value may not translate into fewer symptoms, better daily functioning or longer life.

#Questions worth asking a clinician

• Which biomarker are you measuring, and what could it tell us about my health?
• How accurate is this biomarker test, and what could cause a misleading result?
• Could my medicines, diet, exercise, or other health conditions affect my biomarker results?
• How would the results change my treatment or the need for further tests?
• Will this biomarker need to be measured again, and what would changes over time mean?