What does a PPD test of 5mm indicate?

A PPD test, or purified protein derivative test, is used to determine if someone has been exposed to the bacteria that cause tuberculosis (TB). The result is measured in millimeters of induration, which is the hardened area of skin at the test site.

A result of 5mm induration indicates a positive response, particularly in individuals who are considered to be at very high risk for TB infection. This group includes individuals such as those with compromised immune systems (like HIV patients), recent contacts of active TB cases, or individuals with certain medical conditions or a history that places them at a higher risk of developing TB. In these cases, even a small induration may warrant further evaluation because it suggests active infection or significant exposure.

In contrast, for individuals who are considered low risk or have no risk factors, a 5mm result would typically be interpreted as negative, indicating that they have not been exposed to TB. Understanding the significance of the measured induration is crucial in assessing the risk of TB infection and determining the necessary follow-up actions.