Celery (Api g 1) IgE

If you get an itchy mouth, swollen lips, or worse symptoms after eating raw celery, especially during or after birch pollen season, this test tells you whether your immune system has built a specific antibody against a major celery protein. That answer can help connect the dots between your pollen allergies and your food reactions.

This test looks for IgE (immunoglobulin E) antibodies aimed at Api g 1, the celery protein most closely related to the main birch pollen allergen. A positive result confirms that your body recognizes this specific celery protein, but it is only one piece of the celery allergy picture, and a negative result does not mean celery is automatically safe for you.

What Api g 1 Actually Is

Api g 1 is the main celery protein in a family called PR-10 (pathogenesis-related class 10) proteins. This family includes the main birch pollen allergen and similar proteins in apple, carrot, hazelnut, and soy. Because these proteins share a similar shape, an immune system trained to react to birch pollen can mistake celery's Api g 1 for the pollen it already knows, which is the basis of birch-related pollen-food syndrome.

This test measures your blood level of IgE antibodies that specifically latch onto Api g 1. IgE is the antibody class that drives classic allergic reactions. A higher level means your immune system has built more of these celery-targeted antibodies, raising the probability of a reaction when you eat celery containing this protein.

Oral Allergy Syndrome and Birch Cross-Reactivity

Api g 1 is most often linked to oral allergy syndrome, where eating raw celery triggers itching or tingling in the mouth, lips, or throat shortly after the first bite. In challenge-confirmed celery allergy, about 59 out of 100 patients had IgE to Api g 1, making it a frequent but not universal driver of celery reactions.

Api g 1 behaves as a heat-labile allergen in practice. The protein itself is fairly stable in isolation, but the celery matrix and pH shifts during cooking promote denaturation and reduce IgE binding, which is why many people with isolated Api g 1 sensitization tolerate cooked celery while reacting to raw. There is a catch: research in people with birch pollen allergy and atopic eczema suggests that cooked PR-10 foods can still drive T-cell-mediated late skin reactions, so cooking does not always make celery completely problem-free if you have eczema.

Severe Reactions Often Involve Different Celery Proteins

Severe systemic reactions to celery, including anaphylaxis, are more strongly linked to other celery components than to Api g 1. Api g 7, a celery defensin, is connected to mugwort pollen-related celery allergy and has been associated with a more severe clinical phenotype. In a separate Italian cohort, co-sensitization to mugwort and ragweed defensins (Art v 1 and Amb a 4) was tied to roughly 7-fold higher odds of systemic food reactions, reinforcing that defensin-driven sensitization carries elevated severity risk. Non-specific lipid transfer proteins (Api g 2 and Api g 6) are another route to systemic, often severe celery reactions.

This matters because Api g 7-driven patients can have strong clinical allergy yet test negative on whole celery extract panels. Studies have shown that defensin-driven celery allergy can be missed entirely by extract-based IgE tests, and even crude celery skin testing can fail to flag these patients reliably. If your symptoms have ever gone beyond your mouth (hives, breathing changes, drop in blood pressure), Api g 1 alone is not enough to fully map your risk, and additional components should be tested.

Reconciling High Sensitization With Few Symptoms

A confusing finding in real-world testing: in one study of pollen-food syndrome, none of the patients with celery symptoms had positive Api g 1 IgE, while nine people who tested positive to Api g 1 had no celery symptoms. This looks like a paradox until you understand that IgE level measures the probability of an allergic reaction, not its certainty. Sensitization is the immune system being primed; allergy is the clinical reaction that actually happens. Your test result is a piece of evidence, not a verdict, and it has to be interpreted alongside what your body actually does when you eat celery.

What a Component Panel Adds Over Extract Testing

Standard celery extract tests can miss a substantial fraction of true celery allergy. Adding component-resolved testing changes the picture meaningfully.

Source: Bauermeister et al. (2009); Ballmer-Weber et al. (2024).

What this means for you: if your only celery test has been an extract-based result, especially a negative one, it does not rule out clinically relevant celery allergy. Asking specifically for component testing including Api g 1 and Api g 7 gives a more precise read on what is driving any reactions.

Why One Reading Is Not Enough

A single Api g 1 IgE number is a snapshot of a moving system. IgE production responds to ongoing pollen exposure, which means levels can shift across birch pollen seasons. Avoidance over months to years and pollen-targeted immunotherapy can also change sensitization profiles over time, though direct evidence specifically tracking Api g 1 IgE through interventions is limited.

A reasonable cadence is to get a baseline now, retest in 6 to 12 months if you are pursuing pollen immunotherapy or making major exposure changes, and at least annually if you have a history of reactions. Trending matters more than chasing a target number, because watching the direction of change while paying attention to symptoms is more informative than any single value.

When Results Can Be Misleading

• Symptoms without positive Api g 1: in real-world testing, people with celery symptoms can have negative Api g 1 IgE because their allergy is driven by Api g 7, lipid transfer proteins, or other components that this single test does not cover.
• Positive Api g 1 without symptoms: sensitization alone is not the same as clinical allergy. A positive result in someone who eats celery without trouble may simply reflect cross-reactivity from birch pollen IgE.
• Recent pollen season: birch pollen exposure can amplify IgE responses to cross-reactive proteins like Api g 1, so a test drawn during or just after peak season may run higher than the same test in winter.
• Lab method differences: different immunoassay platforms can give different absolute numbers for the same sample, so trend lines are most reliable when you stay on the same platform.

What to Do With an Unexpected Result

If your Api g 1 IgE is elevated but you tolerate raw celery without symptoms, you are sensitized but not currently allergic, and avoidance is not automatically required. The decision pathway then centers on your history: have you had oral itching, throat tightness, hives, or anything systemic? Has the pattern changed over time?

If you have had any reaction beyond mild oral symptoms, or if you have birch or mugwort pollen allergy combined with food reactions, the next step is a fuller celery component panel including Api g 7, Api g 2, and Api g 6, plus birch and mugwort pollen components. An allergist or immunologist can interpret this combined pattern, decide whether a supervised food challenge makes sense, and discuss whether you should carry epinephrine. Skin testing alone or a single IgE value should not drive a permanent celery avoidance decision in someone who eats it without symptoms, nor should a negative single result reassure someone whose history includes anaphylaxis.