Diagnosis

The principal investigation is the history, in which a story of exposure to allergen followed by allergic rhinitis symptoms is diagnostic, and suggests how to treat or prevent further episodes. Variation in symptoms with respect to the period of the day (e.g., allergy to dust mite is generally worse at night and early in the morning), the season (e.g., pollen allergy), location (e.g., workplace) or other factors, such as administration of drugs, may give important clues to the allergen (1).

Skin prick testing assesses IgE bound to cutaneous mast cells. Its popularity arises from its low cost, simplicity, minimal side effect profile and clearly discernible negative and positive response. It is also easily repeatable.

There is increasing awareness that many patients with either seasonal or perennial symptoms but negative skin tests for allergen sensitivity have local nasal allergy, diagnosable by the presence of allergen-specific IgE in their nasal secretions or a positive nasal allergen challenge or both (2).

Allergen-specific IgE antibody testing, also known as radioallergosorbent testing (RAST), is useful in detecting common allergens like dust mites, pollen and pet dander. It is highly specific but not as sensitive as the skin prick test. It is preferred in situations where:

• percutaneous skin prick testing is not practical or
• a patient is using medication that interferes with skin testing, e.g., antihistamines (3)

Atopy itself is suggested by high serum IgE.

Less commonly used investigation methods include nasal provocation testing.

• nasal cytology (e.g., blown secretions, scraping, lavage, biopsy)
• nasolaryngoscopy
• intradermal skin testing (3)

References:

1. Clinical knowledge summaries, safe practical clinical answers. Allergic rhinitis.
2. Hoyte FCL, Nelson HS. Recent advances in allergic rhinitis. F1000Res. 2018;7:F1000 Faculty Rev-1333; published online 2018 Aug 23.
3. Quillen D, Feller DB. Diagnosing rhinitis: allergic vs. nonallergic. Am Fam Physician 2006;73(9):1583–90.