Biomarker

A biomarker is a characteristic of a biological system that can be measured, compared, and evaluated to determine the health of a living being. Biomarkers can also be used to help determine the progress of an illness or the success of a treatment and to predict the course of an illness in an individual or a group of individuals. Sometimes biomarkers are easy to measure and interpret, while other times more advanced means must be used. Physicians would have a very difficult time diagnosing and treating a patient for any condition without the assistance of biomarkers.

Background

Biomarker is short for biological marker and can refer to any of a host of different aspects of a biological organism that can be measured, compared, and evaluated. Some—for example, taking a pulse measurement to determine heart rate—have existed for nearly as long as humans have attempted to tend to the health of others. Common biomarkers that are assessed at almost every visit to a physician include heart rate, blood pressure, body temperature, weight, and height. A physician assessing the overall health of an individual may also order tests of biomarkers that are detectible in bodily fluids such as blood and urine. These include tests for cholesterol, triglycerides, and blood glucose.

Physicians can use changes in these biomarkers to assess the patient's relative health as well as their health progress over time. For instance, a physician will chart the height and weight of a child at successive visits and match these to a chart that shows the height and weight of many other children of the patient's same age. By comparing the child's growth to the patterns seen in the examinations of many other children, the physician can help to determine if the child's height and weight are appropriate for their age or indicate a possible problem.

Sometimes one of these biomarkers or another procedure will indicate that the patient has a disease. In such cases, the physician can use other biomarkers to determine the status of the illness. For example, if a person's blood pressure reading indicates that the person might have heart disease, the physician can order blood tests and other procedures such as an electrocardiogram. The biomarkers from these tests can help the physician assess the patient's condition and determine what treatment, if any, is needed.

Biomarkers also have uses far beyond routine health care. Scientists have identified markers that can be used to detect or track the status or progression of diseases such as diabetes, heart disease, cancer, multiple sclerosis, Parkinson's disease, Alzheimer's disease, schizophrenia, thyroid disease, and many others. Ways have also been found to test how well a condition is responding to a drug or other therapy.

In some cases, biomarkers can also be used to determine the effects of something in the environment, such as measuring the level of lead or another contaminant in a person's blood to determine if they have been exposed to the substance. A biomarker can also be a substance placed inside the body as an aid to measuring some aspect of its function, such as the use of radioactive iodine to determine how well the thyroid is working. However, the most common usage for the term refers to measuring and evaluating some existing aspect of a biological system to determine its health and/or function.

Overview

Biomarkers that are effective in helping a physician measure health have several characteristics. They are generally easy to measure and do not place either the physician or patient at any significant risk. They perform in a consistent manner regardless of the patient's gender or ethnic background. They show the effects of treatment, improving or worsening depending on medications, diet, etc. Another sign of a good biomarker is that improving it provides a good, cost effective way to better the patient's health. For example, the effects of a lower blood glucose level are so beneficial to the treatment of diabetes that it is worth the cost of treatment to achieve that lower level.

Biomarkers are also objective. This is a key difference between a biomarker and a symptom, although biomarkers can present as symptoms as well. A patient who is having chest pains may take their blood pressure at home. Finding it high, the patient calls the physician and reports that he or she is not feeling well and is experiencing chest pains and high blood pressure. The patient is presenting both as symptoms. However, the chest pains are only a symptom because they cannot be measured in objective terms. People experience pain at different intensities; what some people find bearable is excruciating to others. Pain is therefore a symptom, not a biomarker. A blood pressure reading, on the other hand, meets the requirements of a biomarker because of its consistency (a common baseline number is considered good and deviations from that are generally bad), it is easily measurable, and improvements in blood pressure generally accompany improvements in a patient's health.

These properties of biomarkers also make them useful in developing drugs and other therapies to treat illnesses. For example, for many years, treatments for cancer were aimed at killing the cells in the part of the body where the cancer was located. These treatments would kill indiscriminately, affecting healthy cells as well as those with cancer and often creating additional health concerns for the patient. By identifying certain biomarkers that appear in cancer cells but not in healthy cells, scientists have been able to develop anti-cancer drugs that target the cancer cells but leave the healthy cells alone. Researchers have also identified biomarkers for cancer and other health conditions that allow them to identify these conditions earlier, possibly even before the patient develops symptoms, so preventive treatments can be used. In some cases involving infectious diseases such as influenza, researchers can use these biomarkers to determine how the disease might affect the population and develop immunizations or more effective treatments for the disease.

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