Biomarkers are any measurable characteristics of an organism that reflect a particular physiological state. In medicine, biomarkers are often compounds isolated from serum, urine, or other fluids that can be used as an indicator of the presence or severity of a particular disease state. Biomarkers can also be used to assess the effectiveness of particular therapies in ameliorating the effects of a disease. By using easily obtained and assayed biomarkers to monitor a patient's reaction to a particular drug, it is possible to determine whether treatment is effective for that individual by measuring drug response rate or toxic effects associated with the drug. This information could eventually lead to earlier detection of adverse drug response, reducing the number of costly laboratory tests – and possible other medical interventions – necessary to adjust proper dosage of a drug.
Biomarkers are also important in the development of new drug therapies through the discovery of "druggable targets." In addition to identifying drug targets, biomarkers have the potential to speed development of new disease therapies through the use of "progression" markers to delineate the development and course of a disease. Researchers can use changes in the progression markers to understand if and how a new therapy is successfully slowing – or even reversing – the disease process. Results of studies like these will allow researchers to focus efforts and resources on the most effective therapies, thus reducing the time and cost to bring a new therapy to market and eventually to the patient.
Biomarkers can take many different forms, including particular proteins or peptides (e.g., prostate-specific antigen as an indicator of increased risk for prostate cancer), antibodies (e.g., anti-citrullinated protein antibodies for rheumatoid arthritis), cell types (e.g., white blood cell counts in infection or cancer), metabolites (e.g., phenylalanine in urine of newborns with phenylketonuria), lipids (e.g., cholesterol and other lipid levels in cardiovascular disease), hormones (e.g., thyroid stimulating hormone in Hashimoto's Disease), enzyme levels (e.g., various hepatic enzymes for liver cancer), physiological states such as blood pressure or fever, or imaging studies of particular organs or organ systems (e.g., neural degeneration in Parkinson's Disease). A biomarker can also be a substance introduced into a patient to assess how internal organ systems are functioning, such as radioactive iodine used to measure thyroid function.
Ultimately, biomarkers can be used to detect a change in the physiological state of a patient that correlates with the risk or progression of a disease or with the susceptibility of a disease to a given treatment. Biomarkers hold great promise for personalized medicine as information gained from diagnostic or progression markers can be used to tailor treatment to the individual for highly efficient intervention in the disease process.