Biomarker

A biomarker is a measurable biological feature that indicates a physiological state, disease process, or response to treatment. It may be a molecule, cell, physiological measurement, or pattern in biological data.

Prostate-specific antigen: A protein measured in blood that can indicate prostate disease, including prostate cancer. Its use in prostate cancer screening illustrates both the value and limits of diagnostic biomarkers.
Biomarker assay: A laboratory or clinical test that measures a biological feature in a specimen or organism. Assay design determines which biomarker forms are detected and how reliably they are quantified.
Surrogate endpoint: A biomarker used in place of a direct measure of how a patient feels, functions, or survives. A biomarker can stand in for a clinical outcome only when evidence supports that substitution.
Reproducibility crisis: Difficulty obtaining consistent results when scientific studies are repeated. Unreliable findings can leave proposed biomarkers unsupported outside their original studies.
Troponin: A group of proteins released into blood when heart muscle is damaged. Elevated cardiac troponin is a standard biomarker for diagnosing acute heart injury.
Analytical validity: The extent to which a test accurately and reliably measures the feature it is designed to measure. A biomarker result is useful only if the assay measures it consistently and accurately.
Risk factor: A characteristic associated with an increased probability of developing a disease or adverse outcome. A risk factor predicts future likelihood, while a biomarker may indicate current biology or treatment response.
Batch effect: Systematic variation in measurements caused by processing samples in different groups or runs. Batch effects can mimic biological differences and undermine biomarker discovery.
Hemoglobin A1c: A form of hemoglobin that reflects average blood glucose over roughly the previous two to three months. It provides a biomarker of longer-term glucose control in diabetes.
Clinical validity: The extent to which a measured feature is associated with a clinical condition or outcome. A biological measurement must correlate with the condition it is meant to indicate.

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