Cashew Nut (Ana o 3) IgE Test

If you or your child has had a reaction after eating cashews, or if a routine allergy panel flagged cashew sensitivity, the single most useful follow-up question is whether the antibodies in the blood are aimed at the specific cashew protein that drives real allergic reactions. That protein is called Ana o 3.

Measuring Ana o 3 IgE (the antibody to Ana o 3) gives a clearer answer than a standard cashew extract test, which often flags people as sensitized even when they can eat cashews without trouble. For families weighing the risks of an oral food challenge or trying to understand the chance of a severe reaction, this number can change the plan.

What This Test Measures

Ana o 3 is a 2S albumin, a small, sturdy storage protein concentrated inside cashew seeds. It survives digestion and heating, which is part of why it can trigger reactions throughout the body when eaten. When your immune system mistakes Ana o 3 for a threat, it produces IgE (immunoglobulin E) antibodies that lock onto it. The blood test counts those Ana o 3-specific IgE antibodies.

A standard cashew test looks at the whole nut extract, a mixture of many proteins. Some of those proteins are mild or cross-react with pollen, which is why people often test positive without ever having a real reaction. Ana o 3 sits at the dangerous core of the nut, and antibodies against it correlate closely with actual clinical allergy.

Why It Matters for Cashew Allergy Diagnosis

In a study comparing children with and without confirmed cashew allergy, Ana o 3 IgE separated the two groups better than the standard cashew extract test (a measure called area under the curve was 0.94 for Ana o 3 versus 0.78 for the extract, where 1.0 would be perfect). At a level around 2.0 kU/L, roughly 95 out of 100 children with that result had a real, clinically confirmed cashew allergy.

A pooled meta-analysis confirmed the pattern. At a cutoff near 0.4 kUA/L, Ana o 3 IgE caught about 96 out of 100 cashew-allergic patients (sensitivity 96%) and correctly cleared about 94 out of 100 who were not allergic (specificity 94%). In a Greek pediatric cohort, a slightly lower cutoff of 0.16 kUA/L correctly classified about 97% of children with cashew or pistachio allergy.

What this means for you: a clearly elevated Ana o 3 IgE result strongly supports a real cashew allergy, while a low result helps rule one out. That can spare you or your child from a high-risk oral food challenge, which is the traditional way to confirm or exclude the diagnosis.

Anaphylaxis and Severe Reaction Risk

Cashew is one of the most common triggers of severe allergic reactions in children. In a study of 237 children, those whose only sensitization was to Ana o 3 (monosensitization) had a particularly high risk of severe anaphylaxis, including cardiovascular and respiratory symptoms. In a registry of 1,389 anaphylaxis events, cashew was the most frequent trigger in children.

Higher Ana o 3 IgE levels do not perfectly predict how severe a reaction will be on any given day, but a positive Ana o 3 result identifies a group with meaningful risk. If your number is elevated, that is a strong reason to carry an epinephrine auto-injector and have an action plan in place.

Cashew and Pistachio Cross-Reactivity

Cashew and pistachio are botanically close, and their storage proteins look similar to the immune system. In the Greek pediatric study, IgE to Ana o 3 was highly predictive of both cashew and pistachio allergy. If your Ana o 3 result is positive, it is reasonable to treat pistachio as a likely shared risk until proven otherwise, even if pistachio itself has never been tested directly.

Research-Reported Diagnostic Cutoffs

These cutoffs come from pediatric cohorts using the ImmunoCAP blood test for Ana o 3 IgE. They are illustrative orientation, not universal targets. Your lab may use a different assay or report in different units, and adult data are limited. Compare results within the same lab over time for the most meaningful trend.

Source: Lange et al. 2017; Dang et al. 2021; Savvatianos et al. 2015; Riggioni et al. 2023.

What this means for you: a single Ana o 3 number is not a verdict on its own. It is one piece of evidence that gains meaning when combined with your history of reactions, your cashew extract IgE result, and, in some cases, a supervised food challenge.

Tracking Your Trend

Ana o 3 IgE is not a one-and-done measurement. Some children outgrow cashew allergy, and when they do, their Ana o 3 IgE typically falls substantially over months to years. In a pediatric follow-up cohort, large drops in Ana o 3 IgE predicted tolerance on a later food challenge, while persistent or rising levels suggested ongoing allergy.

If your initial result is elevated, retesting every 12 months is a reasonable cadence for tracking whether the allergy is fading. If you are pursuing a treatment such as cashew oral immunotherapy under medical supervision, more frequent monitoring may be appropriate. A clear downward trend over time, especially a drop of 50% or more, is a stronger signal than any single reading.

When Results Can Be Misleading

IgE testing is generally reliable, but a few situations can blur the picture:

• Sensitization without allergy: a detectable Ana o 3 IgE on the low end does not always mean a real reaction will occur. The correlation with clinical allergy is strong but not absolute, especially at borderline values.
• Assay differences: different laboratory platforms can return different numbers for the same sample. Compare your results within the same lab when tracking trends.
• Recent biologic medications: drugs like dupilumab (used for eczema) have been shown in human studies to lower food-specific IgE levels overall. If you are on a biologic that targets allergic inflammation, your number may understate your true allergic profile.
• Very low total IgE: if your overall IgE production is low, all specific IgE values tend to be small, which can make interpretation of borderline Ana o 3 results trickier.

What to Do With an Abnormal Result

If your Ana o 3 IgE is elevated, the next step is not to retest in a panic. It is to bring the result, along with your reaction history, to an allergist. Helpful companion tests often include cashew extract IgE, pistachio IgE, and selected other tree nut components (such as walnut Jug r 1 or hazelnut Cor a 14) to map the broader nut risk. For severity questions, a basophil activation test may be available in specialty centers.

A clearly positive Ana o 3 result, combined with a history of a reaction, usually means the diagnosis is settled and an oral food challenge is unnecessary. A borderline result with no clear history is the situation where a supervised challenge can resolve uncertainty. Either way, an elevated number is a reason to carry epinephrine, build an emergency action plan, and review labels for cashew and pistachio.