PPD Skin Test | Mendel–Mantoux test | tuberculin skin test (TST)
Tuberculosis remains a global health concern, and timely detection is pivotal for effective management and control. The PPD test serves as an essential tool in identifying individuals who have been exposed to TB bacteria, allowing for early intervention and preventive measures.
The PPD test involves injecting a small amount of purified protein derivative (PPD) derived from TB bacteria just beneath the skin. This triggers an immune response in individuals who have been exposed to TB.
How the PPD Test Works
Upon administration of the PPD solution, the immune system of an individual who has been exposed to TB will recognize and react to the injected proteins. This reaction is typically seen as a raised bump at the injection site.
PPD Skin Test Test Value
Biological Reference Range
|Size Of Erythema||0-10 mm|
|Size Of Induration||0-10 mm|
How is the PPD skin test performed?
A Nurse injects a tiny amount of tuberculin under the skin usually in forearm, A small, pale bump will form at the injection site. After 48 to 72 hours the doctor examines the skin reaction on the injection site.
Note – Tuberculin is a sterile extract of a purified protein derivative (PPD) made from the bacteria that cause TB (Tuberculosis).
PPD Test Results
The size of the raised bump at the injection site is measured and interpreted by healthcare professionals. A larger bump indicates a stronger immune response, potentially suggesting exposure to TB bacteria.
Significance in Tuberculosis Screening
The PPD test is a valuable tool in screening individuals who might have been exposed to TB. It helps identify latent TB infection, where the bacteria are present but not causing active disease. Timely detection of latent TB is crucial to prevent the progression to active TB disease.
Limitations and Considerations
While the PPD test is a useful screening tool, it has limitations. False-positive results can occur due to factors such as prior vaccination with the Bacille Calmette-Guérin (BCG) vaccine, which is used in some countries to prevent TB.
Public Health Implications
The PPD test contributes to public health efforts by identifying individuals who might be at risk of spreading TB to others. It plays a role in contact tracing and implementing preventive measures to contain the spread of the disease.
PPD Test and Active TB Disease
While the PPD test detects exposure to TB bacteria, it does not differentiate between latent TB infection and active TB disease. Additional tests, such as chest X-rays and sputum tests, are needed to confirm active disease.
Future of Tuberculosis Diagnosis
Advancements in diagnostic techniques, including blood-based tests and molecular assays, are reshaping TB diagnosis. These methods offer higher sensitivity and specificity compared to the PPD test.
The PPD test remains a vital tool in the global fight against tuberculosis. By identifying individuals at risk of TB exposure, it aids in early intervention, preventing the progression to active disease, and contributing to public health efforts to control TB transmission.