Celery (Api g 2) IgE

If you have reacted to celery, peach, or mugwort pollen and want to know whether you carry a sensitization that has been linked to severe, body-wide allergic reactions, this is the test that gets specific. It measures a single antibody aimed at one celery protein, not a whole vegetable's worth of possible triggers.

Knowing this number changes how you think about future exposures. In Mediterranean populations, sensitization to this protein has been tied to a pattern of allergy that can produce reactions far beyond the mouth, including anaphylaxis in some cases.

What This Test Actually Measures

The test detects IgE antibodies (a type of allergy antibody your immune system makes) in your blood that are aimed specifically at Api g 2, the non-specific lipid transfer protein found in celery stalks. Lipid transfer proteins, often shortened to LTPs, are small, sturdy plant proteins that survive heat, stomach acid, and digestion better than many other food allergens, which is part of why they sometimes produce serious reactions instead of just mild mouth itching.

Your body produces this antibody through a coordinated response involving B cells (immune cells that make antibodies) and helper T cells. Once made, the antibody attaches to mast cells and basophils, which are immune cells positioned in your skin, gut, and airways that release histamine when triggered. On re-exposure to celery, the antibody recognizes the protein and signals these cells to react.

This is not a general celery allergy test. Celery contains several different allergenic proteins, including Api g 1, Api g 4, Api g 5, Api g 6, and Api g 7. This test only sees one of them. That specificity is the point: each protein carries different clinical meaning.

Why This Single Protein Matters

In an Italian study of 786 people already sensitized to lipid transfer proteins, 25.6% had IgE to Api g 2. In a subgroup of 32 patients with LTP-related allergy, 10 reported symptoms after eating celery stalks, and these reactions mainly took the form of oral allergy syndrome (itching and swelling in the mouth and throat).

A larger Italian analysis of 7,176 patients undergoing molecular allergy testing found that sensitization to celery LTPs (Api g 2 and the related Api g 6) was strongly associated with severe systemic reactions, including anaphylaxis. The protein is not just a marker that you might get a tingly mouth from celery. It is a marker that your immune system recognizes a class of allergens with a real track record of producing dangerous reactions.

Cross-Reactivity With Mugwort and Peach

Api g 2 shares structural features with lipid transfer proteins in mugwort pollen (called Art v 3) and peach (called Pru p 3). This means an antibody trained against one of these proteins can recognize the others. In practice, people with IgE to Api g 2 often also have IgE to these pollen and peach proteins, which can show up as allergic reactions to multiple, seemingly unrelated foods.

This cross-reactivity matters because reactions to celery may signal a broader pattern. Patients with the highest IgE response to Api g 2 in the Italian cohort tended to be those with clinical celery-stalk symptoms, suggesting Api g 2 itself drives some of these reactions rather than being only a passive bystander.

Heat and Digestion Resistance

Unlike many food allergens that break down with cooking, Api g 2 is highly resistant to both heat and simulated digestion in laboratory testing. In the original molecular characterization of the protein, thermal denaturation did not reduce IgE binding, and Api g 2 also survived simulated gastrointestinal digestion. This durability is one reason LTPs are linked to systemic rather than purely oral reactions: the protein can reach the gut intact and still be recognized by the immune system.

This means cooking should not be assumed to make celery safe if you are sensitized to Api g 2. Heat exposure in real meals varies, and the way celery is processed in soups, juices, or seasonings does not match controlled laboratory conditions. A positive result warrants caution with celery in all forms until you and a clinician understand your specific pattern.

How This Compares to a Whole-Celery Allergy Test

A standard celery extract IgE test uses a mix of all celery proteins to detect a general response. It cannot tell you which specific protein your antibodies are aimed at. Component tests like Api g 2 break that picture apart, showing which individual molecules your immune system has flagged.

The clinical meaning differs by region and population. In a Mediterranean LTP-sensitized cohort, Api g 2 was a frequent and clinically relevant finding. In a central European celery-allergic cohort of 79 patients, Api g 2 and Api g 6 were described as not particularly relevant, while Api g 7 emerged as the key marker of severe reactions, and a panel of Api g 1.01, 1.02, 4, 5, and 7 reached 92% sensitivity. The takeaway: one component rarely tells the whole story, and Api g 2 results are most meaningful when interpreted alongside other celery and pollen components.

What Elevated and Low Levels Mean

An elevated result indicates your immune system has produced antibodies to Api g 2. In the context of celery symptoms or a known LTP allergy pattern, this points to an LTP-driven mechanism behind your reactions. In the Mediterranean cohort, elevated Api g 2 IgE in patients with clinical celery symptoms was most often linked to oral allergy syndrome, with severe reactions reported in larger LTP-sensitized populations.

A low or undetectable result means little or no sensitization to this specific protein. It does not rule out celery allergy through a different mechanism, since other celery components (especially Api g 7) can drive reactions on their own. The antibody level itself does not predict how severe your reaction will be. IgE quantity is one piece; the quality of the antibody response, how strongly it binds, and how readily your mast cells respond all influence what happens during a real exposure.

Tracking Your Result Over Time

Allergen-specific IgE levels can shift over months and years. Sensitization patterns may evolve, particularly with ongoing pollen exposure or after dietary changes. A single value gives you a snapshot; serial measurements show whether your immune profile is moving in a direction worth acting on.

For most people pursuing this test, a baseline reading followed by a retest in 6 to 12 months is reasonable, especially if you change your celery exposure, start or stop an allergen immunotherapy, or notice a change in your reaction patterns. After that, annual or biennial retesting is sensible if you remain in an active management plan. Tracking is more informative than any single number, particularly because the relationship between IgE level and clinical reactivity is imperfect.

When Results Can Be Misleading

Specific IgE tests can be positive in people who have never had a clinical reaction. In European data on food allergy more broadly, sensitization (a positive blood test) was found in a substantially larger share of people than true challenge-confirmed allergy, with sensitization rates running many times higher than confirmed clinical allergy. A positive Api g 2 result without symptoms does not mean you have a celery allergy. Conversely, a negative result does not fully exclude reactions driven by other celery components, especially Api g 7.

The clinical meaning of an Api g 2 result also depends on geography and your background sensitization profile. The same number carries different weight in a Mediterranean adult with peach and mugwort allergies than in a central European adult whose celery reactions are pollen-driven.

Decision Pathway for an Unexpected Result

If your Api g 2 IgE comes back elevated, the next step is not to panic but to widen the picture. Pair the result with component testing for Api g 1 (the PR-10 protein), Api g 7 (the defensin), and pollen and peach LTPs such as Art v 3 and Pru p 3. This helps establish whether you have an isolated celery sensitization or a broader LTP syndrome that affects multiple foods.

If you have a clear history of reactions, a referral to an allergist for component-resolved diagnostics, possible basophil activation testing, and, where appropriate, a supervised food challenge is the path that yields actionable answers. An allergist can also help you think through whether you should carry epinephrine, given that LTP sensitization sits within the spectrum that can produce systemic reactions. If the result is positive but you have no symptoms, the action is observational: know it, track it, and have a plan if a reaction ever occurs.