Reactive is a word pathologists use in two different situations. In the first situation, reactive is used to describe cells that look abnormal when examined under the microscope but are not cancer cells. In the second situation, reactive is used to describe the results of a special test such as immunohistochemistry.
1 . Cell that look abnormal when examined under the microscope.
Reactive cells look abnormal. They are called reactive because their abnormal look is caused by something close to the cells. Put another way, the cells are reacting to something around them. Reactive cells are not cancer cells.
Cells can develop a reactive look for many reasons including infection, inflammation, physical stress, and radiation. For example, the cells that line the inside of the stomach may look reactive if the stomach is infected by bacteria (usually a species called H. pylori). Similarly, the cells that line the inside of the esophagus will appear reactive in people who suffer from acid reflux disease.
Reactive is not a diagnosis. Rather it is used to described the cells seen under the microscope. The diagnosis used will depend on where the reactive change is seen (the location in the body) and why it is happening.
2. Results of a special test.
In the second situation, pathologists use the word reactive to describe the results of a special test. The most common test described in this way is called immunohistochemistry. Pathologists often describe cells or tissues that show a positive result as reactive while those that show a negative result as non-reactive.