Tuberculin: Difference between revisions

Latest revision as of 05:25, 16 February 2025

Tuberculin Skin Test[edit]

The tuberculin skin test (TST), also known as the Mantoux test, is a diagnostic tool for tuberculosis (TB). It is used to determine if a person has been exposed to the Mycobacterium tuberculosis bacteria. The test involves the intradermal injection of a purified protein derivative (PPD) of the tuberculin antigen.

Procedure[edit]

The Mantoux test is performed by injecting a small amount of PPD tuberculin into the skin of the forearm. The injection is typically made on the inner surface of the forearm, about 4 inches below the elbow. The site is then observed for a reaction, which is measured in millimeters of induration (swelling) at the site of injection.

Reading the Test[edit]

The test site is examined 48 to 72 hours after the injection. A positive reaction is indicated by a raised, hardened area of induration. The size of the induration is measured and interpreted based on the individual's risk factors and history of exposure to TB.

Interpretation[edit]

The interpretation of the tuberculin skin test depends on the size of the induration and the individual's risk factors:

5 mm or more is considered positive in:

 * HIV-infected persons
 * Recent contacts of TB cases
 * Persons with fibrotic changes on chest radiograph consistent with prior TB
 * Organ transplant recipients
 * Persons who are immunosuppressed for other reasons

10 mm or more is considered positive in:

 * Recent immigrants from high-prevalence countries
 * Injection drug users
 * Residents and employees of high-risk congregate settings
 * Mycobacteriology laboratory personnel
 * Persons with clinical conditions that place them at high risk

15 mm or more is considered positive in any person, including those with no known risk factors for TB.

Limitations[edit]

The tuberculin skin test has several limitations. It cannot distinguish between latent TB infection and active TB disease. Additionally, false-positive results can occur in individuals who have been vaccinated with the Bacillus Calmette-Guérin (BCG) vaccine or exposed to non-tuberculous mycobacteria. False-negative results can occur in individuals with weakened immune systems.

Alternatives[edit]

An alternative to the tuberculin skin test is the interferon gamma release assay (IGRA), a blood test that measures the immune response to specific TB antigens. IGRAs are not affected by prior BCG vaccination and are often used in conjunction with the TST to improve diagnostic accuracy.

Related Pages[edit]

@@ Line 1: / Line 1: @@
-== Tuberculin ==
+== Tuberculin Skin Test ==
-[[File:Mantoux_tuberculin_skin_test.jpg|thumb|A Mantoux tuberculin skin test being administered.]]
+[[File:Mantoux_tuberculin_skin_test.jpg|thumb|right|A healthcare professional administering the Mantoux tuberculin skin test.]]
-'''Tuberculin''' is a protein derivative used in the diagnosis of [[tuberculosis]] (TB). It is primarily used in the [[Mantoux test]], which is a method for detecting [[Mycobacterium tuberculosis]] infection.
+The '''tuberculin skin test''' (TST), also known as the '''Mantoux test''', is a diagnostic tool for [[tuberculosis]] (TB). It is used to determine if a person has been exposed to the [[Mycobacterium tuberculosis]] bacteria. The test involves the intradermal injection of a purified protein derivative (PPD) of the tuberculin antigen.
-== History ==
+== Procedure ==
-Tuberculin was first developed by [[Robert Koch]] in 1890. Initially, it was intended as a treatment for tuberculosis, but it was later found to be ineffective for this purpose. However, it proved useful as a diagnostic tool. The original preparation, known as "old tuberculin," was later refined into "purified protein derivative" (PPD), which is used today.
+The Mantoux test is performed by injecting a small amount of PPD tuberculin into the skin of the forearm. The injection is typically made on the inner surface of the forearm, about 4 inches below the elbow. The site is then observed for a reaction, which is measured in millimeters of induration (swelling) at the site of injection.
-== Composition ==
+=== Reading the Test ===
-Tuberculin is composed of proteins derived from the [[Mycobacterium tuberculosis]] bacterium. The most commonly used form is the purified protein derivative (PPD), which is a standardized preparation that ensures consistent results in diagnostic testing.
+The test site is examined 48 to 72 hours after the injection. A positive reaction is indicated by a raised, hardened area of induration. The size of the induration is measured and interpreted based on the individual's risk factors and history of exposure to TB.
-== Uses ==
+== Interpretation ==
-The primary use of tuberculin is in the [[Mantoux test]], which is a skin test used to determine if a person has been exposed to the tuberculosis bacterium. A small amount of PPD is injected intradermally, and the site is examined after 48 to 72 hours for signs of an immune response, such as induration and redness.
+The interpretation of the tuberculin skin test depends on the size of the induration and the individual's risk factors:
-== Administration ==
+* '''5 mm or more''' is considered positive in:
+  * [[HIV]]-infected persons
+  * Recent contacts of TB cases
+  * Persons with fibrotic changes on chest radiograph consistent with prior TB
+  * Organ transplant recipients
+  * Persons who are immunosuppressed for other reasons
-The Mantoux test is administered by injecting 0.1 mL of PPD into the inner surface of the forearm. The injection should create a small, pale elevation of the skin (a wheal). The test site is then evaluated after 48 to 72 hours for the presence of induration, which is measured in millimeters.
+* '''10 mm or more''' is considered positive in:
+  * Recent immigrants from high-prevalence countries
+  * Injection drug users
+  * Residents and employees of high-risk congregate settings
+  * Mycobacteriology laboratory personnel
+  * Persons with clinical conditions that place them at high risk
-== Interpretation ==
+* '''15 mm or more''' is considered positive in any person, including those with no known risk factors for TB.
-The results of the Mantoux test are interpreted based on the size of the induration and the individual's risk factors for tuberculosis. A larger induration is more likely to indicate a positive result, suggesting TB infection. However, false positives can occur, especially in individuals who have received the [[BCG vaccine]] or have been exposed to non-tuberculous mycobacteria.
 == Limitations ==
-The Mantoux test has several limitations. It cannot distinguish between latent and active TB infection, and it may produce false positive or false negative results. Factors such as [[HIV]] infection, malnutrition, and immunosuppression can affect the test's accuracy.
+The tuberculin skin test has several limitations. It cannot distinguish between latent TB infection and active TB disease. Additionally, false-positive results can occur in individuals who have been vaccinated with the [[Bacillus Calmette-Guérin]] (BCG) vaccine or exposed to non-tuberculous mycobacteria. False-negative results can occur in individuals with weakened immune systems.
-== Related pages ==
+== Alternatives ==
-* [[Tuberculosis]]
+An alternative to the tuberculin skin test is the [[interferon gamma release assay]] (IGRA), a blood test that measures the immune response to specific TB antigens. IGRAs are not affected by prior BCG vaccination and are often used in conjunction with the TST to improve diagnostic accuracy.
-* [[Mantoux test]]
-* [[Robert Koch]]
-* [[BCG vaccine]]
-== References ==
+== Related Pages ==
-* Koch, R. (1890). "The etiology of tuberculosis". Berliner Klinische Wochenschrift.
+* [[Tuberculosis]]
-* Centers for Disease Control and Prevention. "Tuberculin Skin Testing". Retrieved from [CDC website].
+* [[Bacillus Calmette-Guérin]]
+* [[Interferon gamma release assay]]
+* [[Mycobacterium tuberculosis]]
+[[Category:Medical tests]]
 [[Category:Tuberculosis]]
-[[Category:Diagnostic tests]]