What does an induration of 0-4 mm typically signify in TB skin testing?

An induration of 0-4 mm in a tuberculosis (TB) skin test generally indicates a negative result for TB. This measurement signifies that the immune response to the tuberculin purified protein derivative (PPD) is minimal and falls below the threshold that would suggest an infection or exposure to the bacteria that cause TB.

In the context of TB testing, the size of the induration is assessed against established criteria, which take into account various factors such as the individual's risk for TB exposure and immune status. For those at low risk, an induration of less than 5 mm is typically interpreted as negative.

Other potential outcomes in TB testing would involve larger induration sizes indicating different levels of risk, or possibly necessitating further evaluation based on individual circumstances, but in this case, the 0-4 mm range specifically points to a negative conclusion.