PPD是WhatExamination

The itching at the site of the PPD skin test suggests a possible infection with Mycobacterium tuberculosis. It may also indicate prior BCG vaccination or a normal immune response. Further evaluation is needed, including a CT scan, blood tests, and antibody testing to confirm the diagnosis.

It is normal for the site of the PPD skin test to feel itchy. The PPD skin test, also known as the tuberculin test, is a method that uses tuberculin in a skin injection to determine whether the body will produce a hypersensitivity reaction to Mycobacterium tuberculosis. Typically, tuberculin is injected intradermally on the volar surface of the forearm, and the reaction is evaluated after 72 hours.

For the tuberculin skin test (PPD) in pulmonary tuberculosis, a reaction diameter greater than 0.5 cm is considered positive, and greater than 2 cm is considered strongly positive. The larger the induration, the higher the likelihood of active tuberculosis. However, a positive PPD test does not necessarily indicate active tuberculosis. Some individuals who have received the Bacillus Calmette–Guérin (BCG) vaccine may also test positive, as may some individuals previously infected with *Mycobacterium tuberculosis*.

A positive PPD test does not necessarily indicate active pulmonary tuberculosis. A negative PPD skin test suggests no tuberculosis infection; however, a positive or weakly positive result may reflect prior Bacillus Calmette–Guérin (BCG) vaccination or possible TB infection. These results require further evaluation at a hospital, including chest radiography and sputum culture. For patients with strongly positive PPD results…

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Redness and swelling after receiving the PPD injection are generally normal drug reactions, but could also be due to an allergic response; specific circumstances require medical evaluation at a hospital. If a hospital visit is needed, fasting is usually not required, but it's best to avoid applying cosmetics, as they may affect test results. Additionally, maintain a light diet and avoid spicy or other irritating foods.

How to Interpret the PPD Skin Test Result: Criteria for Interpreting the Tuberculosis Skin Test Result - If there is no erythema or pruritus at the injection site, the result is negative. - Erythema measuring ≥0.5 cm but <2 cm at the injection site indicates a positive reaction. - A positive reaction signifies that the body has developed a hypersensitivity response to *Mycobacterium tuberculosis*, indicating prior exposure to tuberculosis; however, it does not necessarily indicate active disease.