Diagnosis is suggested by the clinical history. Consider the following symptoms:
|Immediate allergic reaction||Delayed allergic reaction||Not allergy|
|Skin||urticaria, angioedema||eczema flare||rashes which are not itchy, rashes associated with bruising|
|Gut||nausea, vomiting, diarrhoea||vomiting, colic, diarrhoea (sometimes with blood)||watery diarrhoea with flatus only may suggest lactose intolerance|
|Respiratory tract||cough, stridor, drooling, wheeze, dyspnoea||asthma attack||choking on foods, cough productive of purulent sputum|
|Circulation||faintness, loss of consciousness||palpitations|
Skin prick and blood allergy tests provide supportive evidence for immediate, but not delayed reactions. Both tests can result in false negative and positive results. Where there is doubt a supervised challenge to the allergen is recommended.
More information on skin prick and blood testing can be found in the Resource: Patient leaflet section.