Sensitization vs allergy
A positive test shows that the immune system has produced IgE antibodies. Allergy means sensitization plus reproducible symptoms on exposure.
What a positive result shows
A positive result on a blood allergy test means that specific IgE antibodies against a particular allergen have been detected: pollen, dust mites, mould, animal dander, foods, venoms or their molecular components.
This result shows that the immune system has recognised that allergen and produced IgE against it. In medical terms, this is called allergic sensitization.
Sensitization is not the same thing as allergy.
The difference, in short
Sensitization
The body has specific IgE antibodies against an allergen, but this does not automatically demonstrate that the allergen causes symptoms.
A person can have positive IgE to a food, a pollen or dust mites and still have no clinically relevant manifestations on exposure.
Allergy
Allergy requires sensitization together with reproducible symptoms on contact with the allergen.
To speak of IgE-mediated allergy there must be both a positive test and a matching clinical story: symptoms that appear shortly after exposure and recur in similar circumstances.
A concrete example
A patient may have positive specific IgE to shrimp, yet eat shrimp without urticaria, angioedema, digestive or respiratory symptoms, or anaphylaxis.
In that case we speak of sensitization without demonstrated clinical allergy.