Clinical Review

ABC of allergies: Diagnosing allergy

BMJ 1998; 316 doi: (Published 28 February 1998) Cite this as: BMJ 1998;316:686
  1. Csaba Rusznak,
  2. Robert J Davies

    Allergy to environmental agents can affect almost every organ of the body. Although allergic rhinitis is the commonest manifestation, the lower respiratory tract, the conjunctiva, the skin, and the gastrointestinal tract are frequently affected by allergic disease.

    Age when certain allergies are likely to occur for first time

    • Neonates—Atopic dermatitis, food allergies (milk, egg, nuts)

    • Early childhood—Asthma (house dust mite, pets)

    • Teenagers—Allergic rhinitis (grass and tree pollens)

    • Early adulthod—Urticaria, angio-oedema (aspirin intolerance)

    • Adulthood—Allergy to venom (bee, wasp); nasal polyps

    Allergic diseases are common, and their prevalence is increasing. Accurate diagnosis of triggering or causative allergens is essential for appropriate advice for avoidance and environmental control measures. Although allergic diseases can occur at almost any age, some allergies are most likely to develop for the first time in particular age groups.

    Taking a clinical history

    • A detailed clinical history is vital for diagnosing an allergy

    • Taking a history requires experience, time, and patience

    • Patients should be allowed to give their own account of their symptoms in their own time

    • Structured questions about the patients' history (with particular emphasis on previous allergic diseases—such as childhood eczema, hay fever, and asthma) should be asked

    • Frequency, severity, duration, and seasonality of symptoms should be ascertained, with particular reference to triggering factors, life threatening events, and effects of avoidance measures

    • Patients should be asked about diet; food exclusion; and intolerance to aspirin, colourings, and preservatives

    • Family history should be explored

    • Home, work, and outdoor environmental risk factors should be discussed

    • Groups at particular risk of allergy—such as healthcare and rubber industry workers and children with spina bifida, in whom latex allergy is particularly prevalent—should be identified

    • Patients should be asked about any treatment they are currently using, particularly about antihistamines, topical and oral corticosteroids, and adrenalin autoinjectors


    An immediate relation between exposure to potential allergens and the development of symptoms makes both the diagnosis and identification of allergy straightforward. In …

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