Patient's question:
I previously had my child vaccinated with BCG, and today I went to the health station to check if the BCG vaccination was successful. The doctor examined the scab on my baby's left arm, which was 33mm, and then had the baby undergo a PPD skin test. I previously asked a colleague, and she said her doctor only checked the scab on the left arm and did not perform a PPD test.What help I need: How to interpret the results of the PPD test?
Doctor's answer:
Tuberculin is a substance prepared by heating and filtering a culture of Mycobacterium tuberculosis. Using tuberculin for a skin test on the human body can determine whether the subject has been infected with Mycobacterium tuberculosis. The tuberculin test is an important method for detecting latent tuberculosis infection. There are two types of tuberculin antigen preparations used in the test: Old Tuberculin (OT) and Purified Protein Derivative (PPD). For the tuberculin skin test, typically 0.1 milliliters of tuberculin diluent is administered intradermally at the midpoint of the antecubital fossa on the inner forearm, forming a papule size of 6 to 10 millimeters. 48 to 72 hours after injection, the degree of the body's reaction is determined based on the diameter of the induration at the injection site on the forearm: no reaction indicates a negative result, induration diameter less than 5 millimeters is questionable, induration diameter between 5 and 9 millimeters is weakly positive, induration diameter between 10 and 19 millimeters is moderately positive, and induration diameter greater than 20 millimeters is strongly positive. If, in addition to the induration, blisters, necrosis, or lymphangitis appear on the skin surface, it indicates an extremely positive reaction.