What degree of redness and swelling in a PPD test is considered positive?
Apr 07, 2023
Source: Cainiu Health
Dr. Liu Wan
Introduction
A PPD test result showing induration of 10–19 mm is generally considered positive, while induration of 5 mm or less is considered negative. It should be noted that PPD test results are not absolutely reliable and may sometimes yield false-positive or false-negative outcomes. Therefore, when interpreting PPD test results, doctors need to conduct a comprehensive assessment by considering the patient's medical history, clinical manifestations, and other relevant factors.
In a PPD test, redness and swelling measuring 10–19 mm are generally considered positive, while those within 5 mm are considered negative.
PPD, or skin allergy testing, is a commonly used method to assess an individual's sensitivity to specific allergens. During the PPD test, a healthcare provider applies an allergen to the patient's skin and observes the skin's reaction to determine whether an allergic response occurs.
The results of the PPD test are typically interpreted based on the size and severity of the skin reaction. A positive PPD result usually presents as redness, swelling, itching, or other signs of an allergic reaction, whereas a negative result indicates no observable allergic response. Generally, redness and swelling up to 5 mm in diameter are classified as negative; reactions measuring 10–19 mm are considered positive. When the induration exceeds 20 mm in diameter, or when local blistering, ulceration, or necrosis occurs, the result is classified as strongly positive.
It should be noted that PPD test results are not absolutely reliable and may occasionally yield false-positive or false-negative outcomes. Therefore, when interpreting PPD test results, physicians must also consider the patient’s medical history, clinical symptoms, and other relevant factors for a comprehensive assessment.
