Diagnosing Allergies

Diagnosis is suggested by the clinical history. Consider the following symptoms:

Immediate allergic reactionDelayed allergic reactionNot allergy
Skinurticaria, angioedemaeczema flarerashes which are not itchy, rashes associated with bruising
Gutnausea, vomiting, diarrhoeavomiting, colic, diarrhoea (sometimes with blood)watery diarrhoea with flatus only may suggest lactose intolerance
Respiratory tractcough, stridor, drooling, wheeze, dyspnoeaasthma attackchoking on foods, cough productive of purulent sputum
Circulationfaintness, loss of consciousnesspalpitations

Symptoms in red indicate anaphylaxis

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.