Biomarker (cell)

A biomarker, or biological marker, is defined as a "cellular, biochemical or molecular alteration in cells, tissues or fluids that can be measured and evaluated to indicate normal biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention." Biomarkers characterize disease progression starting from the earliest natural history of the disease. Biomarkers assess disease susceptibility and severity, which allows one to predict outcomes, determine interventions and evaluate therapeutic responses. From a forensics and epidemiologic perspective, biomarkers offer unique insight about the relationships between environmental risk factors.

Three broad classes of biomarkers are prognostic biomarkers, predictive biomarkers and pharmacodynamic biomarkers.

Prognostic biomarkers give intervention-independent information on disease status through screening, diagnosis and disease monitoring. Prognostic biomarkers can signify individuals in the latent period of a disease's natural history, allowing optimal therapy and prevention until the disease's termination. Prognostic biomarkers give information on disease status by measuring the internal precursors that increase or decrease the likelihood of attaining a disease. For example, blood pressure and cholesterol are biomarkers for CVD. Prognostic biomarkers can be direct or indirect to the causal pathway of a disease. If a prognostic biomarker is a direct step in the causal pathway, it is one of the factors or products of the disease. A prognostic biomarker could be indirectly associated with a disease if it is related to a change caused by the exposure, or related to an unknown factor connected with the exposure or disease.

Predictive biomarkers measure the effect of a drug and tell if the drug is having its expected activity, but do not offer any direct information on the disease. Predictive biomarkers are highly sensitive and specific; therefore they increase diagnostic validity of a drug or toxin's site-specific effect by eliminating recall bias and subjectivity from those exposed. For example, when an individual is exposed to a drug or toxin, the concentration of that drug or toxin within the body, or the biological effective dose, provides a more accurate prediction for the effect of the drug or toxin compared to an estimation or measurement of the toxin from the origin or external environment.

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