Celery (Api g 1) IgE Test · Blood

If you get itchy lips, a tingling tongue, or a swollen throat after eating raw celery, this test can help explain why. It looks for a specific kind of immune antibody (called IgE, short for immunoglobulin E) aimed at a single celery protein known as Api g 1.

Api g 1 belongs to a family of plant proteins that closely resemble the main allergen in birch pollen, which is why people with birch pollen allergies often have trouble with celery. The result helps you separate true sensitization from a coincidence, and points you toward the type of celery reaction you are most likely to have.

What This Test Actually Measures

The lab measures IgE (immunoglobulin E) antibodies in your blood that specifically bind Api g 1, the main birch-related celery protein. Api g 1 belongs to a group of plant proteins called PR-10 (pathogenesis-related protein family 10), which look very similar to the major birch pollen allergen Bet v 1.

These antibodies are made by a type of immune cell (B cells that have switched to producing IgE), mostly in lymph nodes and other immune tissues rather than in the blood itself. A positive result means your immune system has been trained to recognize Api g 1, which is what allergists call sensitization. Sensitization is not the same as an allergic illness. It tells you the immune machinery is in place, but symptoms depend on many other factors.

Why Api g 1 Specifically Matters

Celery actually contains several different proteins that can trigger allergic reactions, and they tend to cause different kinds of problems. Api g 1 is the one tied to birch-pollen cross-reactivity, often producing mouth and throat symptoms when you eat raw celery. Other celery proteins, like Api g 7 (a defensin) or Api g 2 and Api g 6 (lipid transfer proteins), are more often linked to whole-body reactions, including severe anaphylaxis.

In adults with celery allergy confirmed by a food challenge (the gold-standard test where you actually eat the food under medical supervision), a majority had IgE against Api g 1. That makes it a major but not universal player. When labs combine Api g 1 with other celery components in a panel, the diagnostic sensitivity for celery allergy rises substantially compared with celery extract alone, without losing accuracy.

Birch-Celery Pollen-Food Syndrome

If you have hay fever in spring and notice your mouth itches after raw celery, carrot, apple, or hazelnut, you may have what allergists call pollen-food syndrome. Your immune system was originally trained on birch pollen, and Api g 1 looks enough like the birch protein that the same antibodies attack it.

These reactions are usually limited to the mouth and throat, a pattern called oral allergy syndrome. They tend to happen with raw celery but often disappear with cooking, because Api g 1 breaks down with heat. There is a catch: even when IgE reactions calm down with cooking, a different arm of the immune system (T cells) can still drive late skin flares in people who also have atopic dermatitis, so cooked celery is not always neutral.

Risk of Severe Reactions

Api g 1 itself is mainly associated with milder, mouth-centered reactions. The proteins more strongly tied to anaphylaxis are Api g 7 (a celery defensin linked to mugwort pollen) and the lipid transfer proteins Api g 2 and Api g 6. Mugwort-related defensin sensitization has been linked to a substantially higher risk of severe systemic reactions in component-level studies.

This matters for how you read your result. A high Api g 1 number does not necessarily mean you are at high risk of going into shock, and a low or negative Api g 1 does not rule out celery allergy. Patients with severe celery anaphylaxis driven by Api g 7 are often negative on routine celery extract testing, which means a normal-looking celery panel can give false reassurance.

How Api g 1 Compares to a Standard Celery Test

A traditional celery allergy test uses an extract made from the whole plant. That extract can miss true allergy in a meaningful share of clinically allergic patients. In studies of people allergic to Api g 7, most were negative to celery extract despite having clear, sometimes severe, reactions. Adding component tests like Api g 1 sharpens the picture by telling you which celery protein your immune system actually targets, and what pattern of reactions you are most likely to have.

What this means for you: if your celery symptoms feel serious, or if you are negative on standard tests but still react, ask about expanding the panel to include Api g 7 and the lipid transfer proteins rather than stopping at extract or Api g 1 alone.

What a Positive or Negative Result Does and Does Not Tell You

A positive Api g 1 IgE shows your immune system is sensitized to a birch-related celery protein. Combined with symptoms after eating raw celery, especially if you also have birch hay fever, that is meaningful. Without symptoms, it just means you carry the antibodies. In real-world multiplex studies of pollen-food syndrome, people with celery symptoms have sometimes been negative for Api g 1, while others with positive Api g 1 results have no celery symptoms at all.

A negative or low Api g 1 does not mean you are safe with celery. Severe celery reactions driven by Api g 7 or lipid transfer proteins can occur with little or no Api g 1 IgE. The test tells you about one protein, not the whole picture.

Tracking Your Trend

A single Api g 1 number is a snapshot of your current sensitization. Antibody levels can drift up or down over time with ongoing pollen exposure, changes in diet, or treatments like allergen immunotherapy. Watching the trend tells you more than any one value, especially if you are considering reintroducing celery, starting immunotherapy for birch pollen, or trying to understand whether your reactions are getting better or worse.

A reasonable approach is a baseline test alongside other relevant components (birch Bet v 1, celery Api g 7, and lipid transfer proteins if relevant for you), a retest in 6 to 12 months if your exposures or symptoms change meaningfully, and a longer interval if everything is stable. Stable trends with stable symptoms are reassuring. A rising number paired with worsening reactions is a flag to revisit your plan.

What to Do With an Out-of-Pattern Result

If your Api g 1 is positive and your symptoms match a birch-celery oral pattern, the next step is usually a conversation with an allergist about expanding the component panel, especially to Api g 7 and the lipid transfer proteins, so you understand your full risk profile. If you have had any reaction beyond mouth itching, such as hives, throat tightness, wheezing, or any episode that needed antihistamines or epinephrine, that is a stronger reason to push for full component testing and to have an action plan in place.

If Api g 1 is negative but you still react to celery, do not assume you are safe. Ask about testing for Api g 7 (defensin) and Api g 2 and Api g 6 (lipid transfer proteins), which are more likely to drive systemic reactions. The gold-standard confirmation in unclear cases is a supervised oral food challenge, and that decision belongs with an allergist who can also build out a written action plan if a true allergy is found.

When Results Can Be Misleading

A few situations can lead you astray with this test:

• Sensitization without symptoms: you can have detectable Api g 1 IgE and eat celery with no problem. The antibodies show your immune system has the machinery to react, not that it will.
• Negative test, real allergy: people allergic to other celery proteins, especially Api g 7, can be negative on extract and on Api g 1 yet still have severe reactions.
• Cross-reactive carbohydrate signals: IgE that binds sugar structures shared across many plants can produce positive results in panels but tends to have low real-world significance compared with Api g 1 itself.
• Symptoms predicted poorly by the number: the size of the IgE value does not reliably predict whether you will react or how severely. Affinity, epitope pattern, and other immune factors matter.

How This Fits Into a Larger Allergy Workup

Api g 1 is most useful when interpreted alongside other components rather than in isolation. A typical fuller picture includes birch Bet v 1 (to confirm the source of the cross-reactivity), Api g 7 (to assess risk of severe celery reactions), and lipid transfer proteins from celery or related foods like peach (Pru p 3) if you have systemic reactions. Multiplex panels like ISAC or ALEX2 can do this in one draw and clarify whether your celery reactivity is birch-driven, mugwort-driven, or part of a broader lipid transfer protein pattern.