What is PPD in Medical Terms?
PPD stands for Purified Protein Derivative. It is a diagnostic tool used to test for exposure to tuberculosis (TB). PPD contains small amounts of the TB bacterium, which is injected into the skin to test for an immune response.
The Importance of PPD Test
TB is an infectious disease caused by the bacteria called Mycobacterium tuberculosis. It mainly affects the lungs, but it can also affect other parts of the body like the brain, bones, kidneys, and spine. TB is a highly contagious disease that spreads through the air when an infected person coughs or sneezes.
PPD to diagnose TB is a crucial tool in the fight against this infectious disease. Early detection of TB is essential to prevent the spreading of the disease and to start appropriate treatment as soon as possible, which can lead to a better prognosis.
How is the Test Performed?
The PPD test involves injecting a small amount of PPD under the skin of the forearm. After about 48-72 hours, the healthcare provider will check the injection site for a reaction.
If the area around the injection site becomes raised or red, this indicates that the person has been exposed to TB before, and their immune system has reacted to the PPD. However, it does not necessarily mean they have TB disease. Further testing is required to confirm if the person has TB disease or not.
Who Should Get Tested with PPD?
The Centers for Disease Control and Prevention (CDC) recommends that certain individuals get tested with PPD. These include:
- People who are at a high risk of getting TB such as those who live or work in close proximity with someone who has TB disease.
- People who have come from a country with a high rate of TB.
- People who have weakened immune systems such as those with HIV or who are undergoing chemotherapy.
- People who work or volunteer in high-risk settings such as healthcare workers or those who work in correctional facilities.
Interpreting PPD Test Results
The results of the PPD test can be either positive or negative. A positive test result indicates that the person has been exposed to TB bacteria in the past, but it does not necessarily mean that they have TB disease. Further testing is required to determine if the person has TB disease or not.
A negative test result indicates that the person has not been infected with TB bacteria or that the response to the bacteria was too weak to be detected by the test. However, false-negative results are possible, especially in individuals with weakened immune systems or those who were recently infected with TB bacteria.
Possible Side Effects of PPD Test
Like any other medical test or procedure, the PPD test has potential side effects. Common side effects include pain, redness, and swelling at the site of the injection.
In rare cases, a severe allergic reaction may occur, leading to difficulty breathing, swelling of the face and throat, and a sudden drop in blood pressure. If a severe allergic reaction occurs, seek medical attention immediately.
Precautions When Getting PPD Test
Before getting a PPD test, inform your healthcare provider if:
- You have any allergies, especially to any of the PPD components.
- You are pregnant or breastfeeding.
- You have a weakened immune system due to a medical condition such as HIV, or if you are taking medications that suppress the immune system.
- You have had a false-positive PPD result in the past.
The PPD test is a crucial tool in diagnosing TB infection. It is a simple and safe diagnostic tool that can help prevent the spread of TB by identifying individuals who have been exposed to TB bacteria. If you think you have been exposed to TB or have any of the risk factors mentioned above, talk to your healthcare provider about getting tested with PPD.
- Q: Why is PPD called a purified protein derivative?
- A: PPD is called a purified protein derivative because it contains a purified extract of Mycobacterium tuberculosis proteins.
- Q: What should I do if I have a positive PPD test result?
- A: If you have a positive PPD test result, your healthcare provider will do additional tests to determine if you have TB disease or not.
- Q: Can the PPD test cause TB infection?
- A: No, the PPD test cannot cause TB infection. It only contains a small amount of purified TB proteins, which is not enough to cause TB infection.
- Q: What is the difference between TB infection and TB disease?
- A: TB infection occurs when a person has been exposed to TB bacteria, but the bacteria are dormant and not active. TB disease occurs when the bacteria become active and cause symptoms.
- Q: Can the PPD test be used to diagnose other types of bacterial infections?
- A: No, the PPD test is only used to test for TB infection. Other types of bacterial infections require different diagnostic tests.
- Centers for Disease Control and Prevention. “Tuberculosis (TB) Testing and Diagnosis.” CDC, 30 June 2020, https://www.cdc.gov/tb/topic/testing/default.htm.
- Mayo Clinic Staff. “Tuberculosis skin test: What you can expect.” Mayo Clinic, 22 June 2019, https://www.mayoclinic.org/tests-procedures/tuberculosis-skin-test/about/pac-20388384.
- Mehta, Surbhi, et al. “Purified Protein Derivative Test (PPD Test-I), False Positive.” StatPearls, 9 Nov. 2020, https://www.ncbi.nlm.nih.gov/books/NBK531469/.