To prevent a severe allergic reaction, the test is started with a very dilute solution. After 10 minutes, the injection site is measured to look for growth of wheal, a small swelling of the skin. Two millimeters of growth in 10 minutes is considered positive.
In order to avoid a severe allergic response, the examination starts with a highly diluted substance. Ten minutes later, the area where the injection was administered is evaluated to check for an increase in wheal size, which manifests as a small swelling of the skin. A two-millimeter expansion within this timeframe is deemed positive.