A tree nut allergy is a hypersensitive immune reaction to proteins found in nuts like walnuts, almonds, cashews, and pecans. This reaction is mediated by Immunoglobulin E (IgE) antibodies and can range in severity, sometimes causing anaphylaxis. Accurate diagnosis is fundamental for patient safety due to the seriousness of the condition and the prevalence of tree nuts in the food supply. Diagnosis must be conducted by a medical specialist, typically an allergist, using a combination of patient history and precise testing methods.
The Initial Clinical Assessment
Diagnosis begins with a thorough discussion between the patient and the allergist, focusing on the patient’s medical history. The doctor asks detailed questions about past reactions, including specific symptoms, how quickly they appeared after eating, and the approximate amount of the suspected nut consumed. Symptoms such as hives, swelling, vomiting, or difficulty breathing are relevant factors in this initial evaluation.
A complete history also involves gathering information on the specific type of nut suspected, any family history of food allergies, and the patient’s general health status. This initial phase helps the specialist determine the likelihood of an allergy and which subsequent diagnostic tests are appropriate. A physical examination contributes to the overall clinical picture before any physical diagnostic tests are ordered.
Screening Methods: Skin and Blood Tests
Screening methods are the first line of physical testing, designed to detect specific IgE antibodies, which are allergic response markers. The Skin Prick Test (SPT) is a quick, minimally invasive procedure where a tiny amount of tree nut extract is placed on the skin, typically the forearm. The area is gently pricked with a small lancet, and if the patient is sensitized, a raised, red, itchy bump (a wheal) appears within 15 to 20 minutes. The wheal is then measured to determine the reaction size.
The specific IgE blood test is another screening tool, measuring the amount of tree nut-specific IgE antibodies circulating in the blood. A blood sample is drawn and sent to a laboratory, with results available after a few days. This test is used when a patient cannot stop taking antihistamines, which interfere with SPT results, or when skin conditions prevent a reliable skin test.
Both the SPT and the blood test indicate sensitization—meaning the immune system has produced IgE antibodies to the nut protein. However, they do not definitively confirm a clinical allergy where symptoms would occur upon consumption. These screening tests provide quantitative data, such as a wheal size of 8 millimeters or greater on the SPT or a specific IgE level of 15 kU/L or more, which are highly suggestive of an allergy for certain tree nuts.
However, many individuals with positive results may not experience a clinical reaction when consuming the nut. The allergist must interpret these numerical results alongside the patient’s history. These tests alone cannot predict the severity of a future reaction.
The Definitive Diagnosis: Oral Food Challenge
When the clinical history is ambiguous or screening tests are inconclusive, the Oral Food Challenge (OFC) is the gold standard used to confirm or rule out a clinical tree nut allergy. This test determines if the patient reacts to the actual consumption of the nut, not just the presence of IgE antibodies. The OFC is a complex, risk-intensive procedure that must only be performed under the direct supervision of an allergy specialist in a medical setting with immediate access to emergency equipment.
The procedure involves giving the patient small, gradually increasing doses of the suspected nut over several hours. The nut is often crushed and mixed into a food like yogurt to aid consumption, with the dose increased every 15 to 20 minutes. Medical personnel closely monitor the patient for any signs of an allergic reaction. Reactions can range from mild symptoms like hives to severe anaphylaxis requiring immediate treatment, such as an epinephrine injection.
The challenge is stopped immediately if a reaction occurs, confirming the allergy; otherwise, a negative result indicates the patient can safely consume the nut. This test is valuable for patients avoiding a nut based on a positive screening test but who have never actually consumed it. The OFC provides the most definitive evidence of whether a patient is truly allergic, allowing for the safe reintroduction of the food and reducing unnecessary dietary restrictions.
Interpreting Results and Management
The allergist synthesizes all the information—the patient’s detailed history, the quantitative results from the skin and blood tests, and the outcome of the Oral Food Challenge—to establish a definitive diagnosis. For example, a clear history of a reaction, high specific IgE levels, and a positive OFC confirm a clinical tree nut allergy. Conversely, a positive screening test coupled with a negative OFC means the patient is sensitized but tolerant and does not need to avoid the food.
Following a confirmed diagnosis, the next steps focus on patient management to ensure safety.
Avoidance and Label Reading
The foundation of management is strict avoidance of the identified tree nut and any foods that may contain it. This includes training on how to read food labels carefully to identify hidden allergens.
Emergency Action Plan
Patients are provided with an emergency action plan and a prescription for an epinephrine auto-injector (e.g., EpiPen or Auvi-Q). This device is the first-line treatment for a severe allergic reaction, and patients and their families must receive training on its proper and timely use.