Allergy diagnostics

Allergic history taking

Before ordering any laboratory or instrumental tests, the physician must assess the overall clinical picture of the disease. A detailed patient interview helps narrow down the suspected allergens and select the optimal examination method.

Particular attention in taking an allergic history is paid to the patient's previous reactions to the administration of medical serums and drugs. In addition, the following factors are thoroughly analyzed:

• External exposures: identification of domestic or specific occupational hazards with which the patient regularly comes into contact.
• Genetic factor: assessment of hereditary predisposition to allergic reactions in blood relatives.
• Chronobiology: determination of the seasonality of symptom manifestation (e.g., exacerbations during the flowering period of certain plants).

Skin prick tests

Prick tests are one of the basic instrumental methods for detecting sensitization. Standardized panels of allergens are used for this purpose: food, pollen, domestic, insect-related, and others.

Procedure technique:

1. The test is usually performed on the skin of the forearm or back.
2. Drops of suspected allergens are applied to the skin surface (up to 10–20 antigens per session).
3. A scratch is made through the drop—a light, superficial disruption of the epidermis integrity using a special instrument.

Evaluation of the local reaction (interpretation):

• Negative result: skin changes are completely absent.
• Doubtful result: only minor hyperemia (redness) is observed around the scratch.
• Positive result: a characteristic wheal forms at the application site. The severity of the allergic reaction is directly proportional to the size of this wheal.

Provocation and patch tests

If prick tests are uninformative or further diagnosis is required, other methods are used, the choice of which depends on the type of pathology and the route of antigen entry into the body.

Provocation tests Their main goal is to simulate an allergic reaction upon direct contact of the allergen with the target organ, which in allergology is called the "shock organ". Routes of administration can vary:

• Intranasal — application of the allergen to the nasal mucosa.
• Oral — administration via the gastrointestinal tract.

Patch tests This method is the primary indication for diagnosing contact dermatitis. Special plates with applied allergens are fixed to the patient's skin for an extended period (up to two days). After removing the plates, the physician evaluates the result: the test is considered positive if inflammatory elements (erythema or papules) are detected.

Laboratory diagnostics: cytokines and IgE

Immunological blood testing confirms the allergic nature of the disease. The main laboratory markers are:

• Cytokine profile: activity is assessed by the $T_{H}2$-type. Interleukins IL-3, IL-4, and IL-13 are of particular importance because they stimulate the excessive synthesis of immunoglobulin E.
• Immunoglobulin E (IgE) level: under physiological norms, this protein is practically undetectable in blood serum. During the development of allergic pathology, its concentration increases manifold.

Importance of differential diagnosis The possibility of false-positive results should be considered. A spontaneous increase in IgE levels may indicate the presence of other severe pathologies rather than an allergy. These include:

• Parasitic infestations (parasitoses).
• Fungal infections (mycoses).
• Viral infections (including HIV).
• Oncohematological diseases (e.g., lymphomas).

What else to study on this topic

• Mechanism of type 2 T-helper ($T_{H}2$) activation and interleukin synthesis
• Classification and types of allergen panels
• Pathogenesis of contact dermatitis
• Differential diagnosis of allergy and lymphoma by IgE levels

Other topics in the section "Features of immunity in various locations..."

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.