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Screening for Allergy - keeping it simple

IgE-mediated allergy is common - as many as 40% of adults in the UK are immunologically atopic (i.e. with raised serum IgE). About half of these go on to experience clinical atopy - with symptoms that often take them to their doctor. The exact ways in which the clinical syndromes are precipitated are not clear, but whatever the reason, patients are becoming more interested in allergy, with considerable press and advertising. Try counting how many pictures of house dust mites you can see in the average quality daily!

So what does the GP do when confronted with patients with symptoms that could be allergy? How is the decision made whether to seek advice from an allergy clinic?

In a paper published in 1980, Dr Terry Merrett demonstrated that some cheap diagnostic tests and a good history could help make an effective decision. Three pieces of information are needed:-
  • Serum total IgE.
  • Patient questionnaire.
  • Specific tests for pollen, dust mite and cat epithelium (the three most common inhaled allergens).
The paper describes how 95% of patients with IgE antibodies to specific allergens are positive to cat, mite or pollen, as well as other specific allergens. Used in conjunction with either a raised total IgE or a positive symptom score by questionnaire, 265 of 275 patients were correctly identified (96.3% of patients with IgE-mediated disease).

In a control group, only 65 of 150 had two positive scores, and none was positive for pollen, cat or mite. It is possible, then, to screen those patients with specific allergies with high sensitivity, leading to more effective diagnosis, referral and treatment.

This is a good read, with ideas that have stood the test of time. It contains the full patient questionnaire, and computer programmes have been written to generate expert systems reports from the questionnaire.

References:

  1. Merrett et al, Allergy, 1980 35: 491-501.
  2. Pantin et al, Clin Allergy 1978 8: 227-233.

Questions to be Answered

Q: What need is met by this test?
A: Rapid diagnosis of 95% of patients with inhaled allergies.
Q: What happens at present?
A: Not clear - many patients may not be tested, while others may be tested for sensitivity to many different allergens.
Q: Is quality improved?
A: Sensitivity is increased.
Q: What is the capital cost?
A: Nil for clinicians. Allergy testing is available at least at regional level. Computer software for questionnaire is not available.
Q: What is the revenue cost?
A: About £15 per case, much less than multiple allergen testing.
Q: What is the likely cost per million population?
A: No general estimate because of different clinical policies.
Q: Will this increase or decrease the total cost of secondary care?
A: Diagnosis will be reached faster. This will reduce costs in those cases. None of the papers gives adequate costs analysis.
Q: What is the effect on the total cost (primary + secondary)?
A: Will have little effect on primary care costs.

Advice to Purchasers

  • will increase quality or effectiveness
  • cost neutral if other tests done less often
  • Research/review needed for clarification

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