A history of consistent allergic signs and symptoms after the ingestion of a tree nut is the first step in diagnosing a tree nut allergy. An allergist will use this history in conjunction with a physical exam to guide the choice of additional diagnostic tests.
The skin prick test is the most common diagnostic test and involves introducing the allergen into the skin through a small prick with a special tool. If IgE antibodies to tree nuts are present, the area that was pricked will swell. A swollen area 3 mm or greater in size is usually considered positive for an allergy, although some clinicians prefer an 8 mm or greater standard to decrease the chance of a false positive.[1] Blood tests that detect food-specific IgE antibodies may also be used to aid in the diagnosis.
Although these diagnostic tests are helpful, they do not predict the severity of a person’s allergic reaction, nor are they useful in people without a history of allergic signs and symptoms (given the frequency of false positives). In some cases, an oral food challenge, which consists of gradual consumption of the allergen under direct medical supervision, may be recommended to confirm the allergy.[2][3] Ideally, allergy testing is done yearly because some allergies change or resolve over time.