Biological markers

A biomarker, or biological marker, generally refers to a measurable of some biological state or condition. The term is also occasionally used to refer to a substance whose detection indicates the presence of a living organism.

Biomarkers are often measured and evaluated to examine normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention. Biomarkers are used in many scientific fields.

The widespread use of the term "biomarker" dates back to as early as 1980. The term "biological marker" was introduced in 1950s. In 1998, the National Institutes of Health Biomarkers Definitions Working Group defined a biomarker as "a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention."

In medicine, a biomarker can be a traceable substance that is introduced into an organism as a means to examine organ function or other aspects of health. For example, rubidium chloride is used as a radioactive isotope to evaluate perfusion of heart muscle.

It can also be a substance whose detection indicates a particular disease state, for example, the presence of an antibody may indicate an infection. More specifically, a biomarker indicates a change in expression or state of a protein that correlates with the risk or progression of a disease, or with the susceptibility of the disease to a given treatment.

Other biomarkers can be based on measures of the electrical activity of the brain (using Electroencephalography (so-called Quantitative electroencephalography (qEEG)) or Magnetoencephalography), or volumetric measures of certain brain regions (using Magnetic resonance imaging) or saliva testing of natural metabolites, such as saliva nitrite, a surrogate marker for nitric oxide. One example of a commonly used biomarker in medicine is prostate-specific antigen (PSA). This marker can be measured as a proxy of prostate size with rapid changes potentially indicating cancer. The most extreme case would be to detect mutant proteins as cancer specific biomarkers through Selected Reaction Monitoring (SRM), since mutant proteins can only come from an existing tumor, thus providing ultimately the best specificity for medical purposes.

...
Wikipedia