InstalabCelery (Api g 2) IgE Test Blood
Should you take a Celery (Api g 2) IgE test?
This test is most useful if any of these apply to you.
About Celery (Api g 2) IgE
If you have ever felt your mouth itch after eating raw celery, broken out in hives at a salad bar, or had a stronger reaction to celery alongside peach or mugwort allergy, this test helps explain what is happening inside your immune system. It looks for IgE antibodies (the immune molecules that drive allergic reactions) directed at one specific celery protein, Api g 2 (a non-specific lipid transfer protein, or nsLTP).
Api g 2 belongs to a family of plant proteins that survive heat and digestion better than most other food allergens, which is why sensitization to them has been tied to more severe, whole-body reactions in some people. Knowing whether your IgE recognizes this specific protein, rather than just celery in general, gives a sharper read on what kind of allergy you have and how it might behave.
What This Test Actually Measures
This is a blood test for IgE antibodies (the immune system's allergy-triggering antibodies) that specifically bind to Api g 2, the lipid transfer protein found in celery stalks. Lipid transfer proteins, or LTPs, are small plant proteins that ferry fatty molecules across plant cell membranes. They are abundant in the skin and outer parts of fruits, vegetables, and pollen, and they are known for being unusually tough.
Most allergy tests use a celery extract, which is a mix of every celery protein at once. Component testing like this one isolates a single protein. That matters because different celery proteins predict very different kinds of allergic reactions. Api g 2 sits in the LTP family, alongside the peach LTP Pru p 3 and the mugwort LTP Art v 3, and IgE against one of these often cross-recognizes the others.
Why Api g 2 Sensitization Matters
Among people in Mediterranean populations who are already sensitized to plant LTPs, about one in four carries IgE against Api g 2. In an Italian study of 786 LTP-sensitized adults, 25.6% had IgE to Api g 2, and many also reacted to mugwort LTP (Art v 3) and peach LTP (Pru p 3). In a separate Italian analysis of 7,176 patients tested for plant defensin allergens, celery LTPs (Api g 2 or the related Api g 6) were detected in 21% of the defensin-sensitized subgroup, and this nsLTP signal was strongly tied to severe systemic reactions.
In that Italian LTP cohort, 10 out of 32 patients with confirmed LTP allergy reacted after eating celery stalks. Most had oral allergy syndrome (itching or swelling limited to the mouth and throat), some had angioedema (deeper swelling), and one had anaphylaxis. Patients with the strongest Api g 2 IgE response in lab cross-blocking tests tended to be the ones with actual celery stalk symptoms.
Reconciling a Counterintuitive Finding
Not every population tells the same story about Api g 2. A central European study of 79 celery-allergic patients concluded that Api g 2 and Api g 6 "were not relevant" in their cohort, and that a different protein, Api g 7 (a defensin-like protein tied to mugwort cross-reactivity), was the main driver of severe anaphylaxis. The same molecule can carry heavy clinical weight in one population and very little in another.
The way to hold both findings together: Api g 2 is a marker of one specific allergic phenotype, the LTP syndrome, which is common in Mediterranean regions and rarer further north. A positive Api g 2 IgE result tells you that you fit the LTP phenotype. It does not, on its own, predict how severe your reactions will be, and a negative result does not rule out celery allergy driven by a completely different celery protein.
The LTP Syndrome Connection
Lipid transfer proteins are the reason a single allergic person can react to peach skin, celery stalks, walnut, hazelnut, and certain pollens. Api g 2 shares structural similarity with Pru p 3 (peach) and Art v 3 (mugwort), and IgE that recognizes one often recognizes the others. In lab experiments, blocking IgE to one of these LTPs partially blocked binding to the others, which is direct evidence of overlapping antibody targets.
There is one practical consequence of LTP biology worth knowing. In the same lab experiments, heating Api g 2 to 95°C for 15 minutes destroyed its ability to bind IgE, while peach LTP held up better. That suggests Api g 2 may be less stable than some of its cousins, though laboratory heat-stability does not always match what happens during real digestion.
How Api g 2 Compares to Other Celery Components
| Celery Component | What It Signals | Typical Clinical Pattern |
|---|---|---|
| Api g 1 (PR-10 protein) | Cross-reactivity with birch pollen | Usually mild, mouth-limited reactions |
| Api g 2 (lipid transfer protein) | LTP syndrome, often Mediterranean | Stalk reactions, sometimes systemic |
| Api g 7 (defensin-like) | Mugwort-celery-spice syndrome | Often severe, including anaphylaxis |
Source: Findings drawn from Gadermaier et al. 2011 (Italian LTP cohort), Ballmer-Weber et al. 2024 (central European celery allergy cohort), and Scala et al. 2025 (Italian molecular allergy study).
What this means for you: a celery extract test can come back positive without telling you which protein is driving it, and a single component result like Api g 2 only shows you one slice of the picture. If you have had real reactions to celery, the most informative workup pairs Api g 2 with other celery components and with mugwort and peach LTPs.
What Elevated Levels Suggest
A positive Api g 2 IgE result means your immune system has produced antibodies against this specific celery protein. It indicates sensitization, which is the immune system's recognition of an allergen, but sensitization is not the same as clinical allergy. Population studies of food allergy in Europe show that 16.6% of people test positive for food-specific IgE while only 0.8% have confirmed food allergy on challenge testing, so a positive lab result without symptoms is common.
What raises the clinical significance of an Api g 2 result is the combination of a positive antibody and a history of real symptoms after eating celery or related foods. Higher antibody levels generally raise the probability of a true reaction, but the strength of the antibody (how tightly it binds) and the breadth of proteins it recognizes matter as much as the absolute number on the report.
When Results Can Be Misleading
A few situations can produce results that do not match what your body actually does with celery:
- Asymptomatic sensitization: you can have IgE to Api g 2 without ever reacting to celery. The lab result alone, without a clinical history, is not a diagnosis.
- Cross-reactivity from pollen exposure: people sensitized to mugwort or peach LTPs can test positive for Api g 2 because the antibodies recognize the shared LTP shape, not because celery is the primary problem.
- Component mismatch: if your celery reactions are actually driven by Api g 7 (the defensin) or Api g 1 (the PR-10 protein), an Api g 2 test alone will miss them and may give false reassurance.
- Geographic variability: Api g 2 carries different weight in different populations. Most evidence comes from Mediterranean cohorts, and the same result may mean less in regions where Api g 7 dominates.
Tracking Your Result Over Time
Specific IgE levels can drift with allergen exposure, pollen seasons, and broader immune changes. A single number is a snapshot, not a verdict. If you are working through a suspected celery or LTP allergy, the more useful pattern is to test, document your symptoms over the next several months, and retest if your symptoms or exposures change. Plan on a baseline measurement, a retest at 6 to 12 months if you are actively changing your diet or trying immunotherapy, and at least annual checks if you are tracking a known sensitization.
Trending across time also helps when other LTPs are involved. If your peach LTP (Pru p 3) and mugwort LTP (Art v 3) IgE are rising alongside Api g 2, your overall LTP phenotype is intensifying, even if no single number crosses a dramatic threshold.
What To Do With an Out-of-Pattern Result
If your Api g 2 IgE comes back positive and you have had reactions consistent with celery or LTP foods, the next step is component-resolved testing for the rest of the picture: Pru p 3 (peach LTP), Art v 3 (mugwort LTP), and the other celery components, especially Api g 1 (PR-10), Api g 4 (profilin), Api g 5, and Api g 7 (defensin). This builds a map of which protein families are driving your symptoms.
If your Api g 2 IgE is positive but you have no symptoms, the result on its own does not warrant restriction. If you have had reactions and Api g 2 is negative, the workup is not finished, because Api g 7 or other components can drive celery allergy independently. In either case, an allergist with experience in component-resolved diagnostics is the right partner, particularly if reactions have ever extended beyond the mouth or required emergency care.