How an allergy result is interpreted
Tests show whether sensitization to an allergen exists. Allergy means sensitization plus reproducible symptoms on exposure.
The result is read in clinical context
An allergy result is always interpreted in clinical context. Allergy tests do not answer the question do I have an allergy on their own. They show whether or not sensitization to a particular allergen exists.
What a positive result means
A positive specific IgE or skin prick test result indicates that the immune system recognises that allergen and has produced an IgE response. This is called sensitization.
Sensitization is not the same thing as allergy. A patient may have positive IgE to a food they tolerate perfectly well, or to an inhalant allergen without relevant symptoms on exposure.
Allergy means sensitization plus compatible, reproducible symptoms on exposure to the allergen. For example, positive IgE to cat is clinically relevant if the patient develops sneezing, runny nose, itchy eyes or cough when entering an environment with cats. If there are no symptoms, the result may represent sensitization alone.
What a negative result means
A negative result does not always rule out allergy. There can be situations in which:
- the test does not include the relevant allergen;
- the extract does not contain the right component;
- the reaction is not IgE-mediated;
- the history points to a different mechanism.
The number is not read mechanically
The numerical value of specific IgE matters, but it is not interpreted mechanically. A higher value can increase the probability of a reaction in certain contexts, but it does not perfectly predict severity.
The physician will take into account the type of allergen, the molecular component, the history of the reaction, the age of the patient, asthma, cofactors and the real exposure.