Spirometry and lung function tests These are used to confirm whether asthma is the cause of wheeze, cough or breathlessness. Challenge tests using a spirometer and an allergen is useful for proving that a specific allergen is responsible for inducing asthma and is useful where occupational allergic asthma is suspected. This Is a test for measuring the degree of nasal blockage, and can also be used for challenge tests to confirm whether an allergen causes rhinitis. A good clinical history is vital for diagnosis of an allergy. False positive and negative results are possible, albeit rarely, but a thorough history combined with appropriate tests will confirm which allergens are responsible for an allergic disease.
Blood tests performed by commercial companies are a case in point.
If a blood test showed IgE antibodies to a range of allergens but the patient has no symptoms to the allergens, then the patient has been sensitised to the allergens but is not yet allergic. In my own case, when suffering from urticaria, a RAST measurement of my serum showed that I had antibodies to grass and tree pollen, wheat and aspergillus fumigatus. As yet, I have no symptoms to these allergens, but could have been inappropriately advised to avoid wheat, with all the inconvenience involved when an elimination diet and symptom diary showed that tomatoes were one of the triggers. Although I have been sensitised to these allergens, probably through handling the allergens for testing patients, I do not qualify as allergic to them. The newer non-sedating antihistamines are much more patient friendly and reduce the risks of accidents to users.