Procedure and product
For mass screening in pediatric practice, the standardized Mantoux test is used. Purified tuberculin is used as the diagnostic agent. It is a specific protein filtrate obtained from a mixture of M. tuberculosis and M. bovis cultures. Notably, these mycobacteria are inactivated (killed) by heating prior to use.
The standard dosage for the test is exactly 2 tuberculin units (TU) contained in 0.1 ml of injection solution. The technique requires strict adherence: the product is administered exclusively intradermally. The injection site is the volar surface of the forearm.
To correctly read the results, exactly 72 hours must elapse. Evaluation is performed by measuring only the transverse diameter of the resulting infiltrate (papule) using a transparent millimeter ruler.
Criteria for evaluating results
The interpretation of the test depends directly on the presence and exact size of the papule or hyperemia (skin redness). After 72 hours, reactions are divided into four main categories:
- Negative reaction: recorded when both papule and hyperemia are completely absent (skin at the injection site is unchanged).
- Doubtful reaction: stated when a small papule measuring 2 to 4 mm is present, or if only hyperemia of absolutely any size is observed, but without the formation of characteristic induration.
- Positive reaction: formation of a papule with a diameter of 5 mm or more.
- Hyperergic (excessive) reaction: diagnosed when the papule size reaches 17 mm or more. This category also includes reactions accompanied by local complications: vesicle formation, necrosis, or inflammation of lymphatic vessels (lymphangitis). The presence of these complications makes the reaction hyperergic regardless of the actual size of the papule itself.
Clinical interpretation and significance
Detecting a positive reaction in a child is not a definitive sign of disease and always requires differential diagnosis. A positive reaction can develop for two reasons:
- Infectious allergy: the result of a true infection of the body with a wild-type strain of tuberculosis mycobacteria.
- Post-vaccination allergy: a normal immune response of the body resulting from prior vaccination or revaccination against tuberculosis (BCG vaccine).
In clinical practice, a special role is played by tuberculin conversion — the initial appearance of a positive reaction following previous negative results. This is an important diagnostic marker of infection. If a hyperergic reaction is detected, it indicates a high probability of an active tuberculous focus in the body.
The main goals of tuberculin skin testing in children are mass screening, early detection of infection, and selection of candidates for revaccination (BCG).
Comparison: Mantoux and Diaskintest
To assess the specific reactivity of the body, two tests are used that complement each other organically. Unlike the screening Mantoux test, Diaskintest (a test with recombinant tuberculosis allergen) has different objectives and composition.
Its mechanism of action is also based on intradermal administration, but the product contains two recombinant proteins. The key difference from purified tuberculin is that these proteins are specific only to actively multiplying Mycobacterium tuberculosis (MTB).
The evaluation criteria for Diaskintest differ:
- Positive reaction: formation of a papule of absolutely any size.
- Hyperergic reaction: papule size of 15 mm or more, as well as the presence of vesicles.
The objectives of using Diaskintest in children are: verification of diagnosis, precise assessment of the activity of the infectious process, and monitoring the effectiveness of specific treatment.
Papule sizes for evaluating the Mantoux test: 0-2-5-17. Negative (0 mm), Doubtful (2-4 mm), Positive (5 mm and more), Hyperergic (17 mm and more).
Class and exam questions
What exactly is measured when evaluating the Mantoux test?
Only the transverse diameter of the resulting infiltrate (papule) is measured. Hyperemia is measured only in the absence of induration.
What can cause a positive test if the child is not sick?
A positive reaction is often a post-vaccination allergy — a normal immune response to prior BCG vaccination or revaccination.
What is the main difference between Diaskintest and tuberculin?
Diaskintest contains recombinant proteins that are specific exclusively to actively multiplying tuberculosis mycobacteria.
What is tuberculin conversion?
This is the initial appearance of a positive reaction in a patient after a series of previous negative results, which is an important marker of infection.
What else to study on this topic
- Differential diagnosis of infectious and post-vaccination allergy
- Tuberculin conversion: pediatrician's tactics
- Indications for BCG revaccination based on tuberculin testing results
- Local complications of hyperergic reactions (lymphangitis, necrosis)
- Use of Diaskintest to monitor the effectiveness of specific treatment
Master the entire topic in the Pediatrics course
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Other topics from the section «Chapter 12. Infectious and parasitic diseases»
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