Immunological Basis and Status of the Method
In microbiological and infectious practice, the allergic method is not universal. It has an auxiliary status and is used only for a specific, strictly limited range of infections.
The foundation of this type of diagnostics is the ability of the immune system to form specific memory. Upon contact with a pathogen or after the administration of a vaccine strain, the body becomes sensitized. If such a patient is injected with a specific antigen (allergen), a delayed-type hypersensitivity (DTH) reaction develops, which in the Gell and Coombs classification is designated as a type IV reaction. The main way to visualize this reaction is through skin allergy tests.
Technique and Interpretation of Results
For diagnostics, a standardized diagnostic preparation containing antigens of the target microorganism is administered to the patient.
There are two main methods of allergen administration:
- Intradermal — most commonly used. The preparation is injected into the middle third of the flexor surface of the forearm.
- Percutaneous (scarification test) — used less frequently. In this case, the allergen is applied to the skin, after which superficial scratches (scarifications) are made through a drop of the preparation.
Since the mechanism relies on delayed-type hypersensitivity, an immediate reaction does not occur. Results are evaluated strictly in a delayed manner — after 48–72 hours. The main diagnostic criterion confirming organism sensitization is the formation of an inflammatory infiltrate (papule) at the administration site. The physician evaluates the mere presence of the papule and measures its size.
Diagnostic Preparations
Each infectious disease uses its own specific preparation, the name of which is usually derived from the name of the pathogen.
| Preparation | Infectious Disease | Note (Eponymous Test) |
|---|---|---|
| Tuberculin | Tuberculosis | Mantoux test |
| Brucellin | Brucellosis | Burnet test |
| Tularin | Tularemia | - |
| Toxoplasmin | Toxoplasmosis | - |
| Mallein | Glanders | - |
| Anthracin | Anthrax | - |
| Pestin | Plague | - |
| Ornitin | Ornithosis | - |
Allergy to Opportunistic Flora and In Vitro Tests
Sensitization of the body is possible not only to strict pathogens, but also to representatives of normal or opportunistic microflora. The development of DTH to such microbes is of great clinical significance: this allergy often becomes the leading mechanism in the pathogenesis of various chronic diseases. A wide variety of organ systems can be affected: the gastrointestinal tract, respiratory tract, kidneys, skin, and joints.
Allergens that maintain such chronic inflammation can include:
- Staphylococci and streptococci;
- Pneumococci;
- Escherichia (E. coli);
- Proteus;
- Pseudomonas aeruginosa.
In addition to classical skin tests performed in vivo, there are laboratory variations of the allergic method performed in vitro (in vitro). These include the neutrophil damage reaction and the blast transformation reaction with the addition of corresponding allergens.