Celery (Api g 6) IgE

If you have unexplained reactions after eating celery, or you carry a diagnosis of celery allergy without a clear culprit, knowing exactly which celery proteins your immune system targets can change how you approach food, pollen seasons, and travel. This test looks at one specific celery protein, called Api g 6, that belongs to a family of plant molecules linked to systemic reactions in some people.

Api g 6 is one of several celery components used in modern allergy diagnostics. The bigger picture is that celery allergy is rarely a single story. It is shaped by which exact proteins your immune system has learned to recognize, and Api g 6 is one piece of that puzzle.

What This Test Actually Measures

This is a blood test for IgE (immunoglobulin E) antibodies that recognize Api g 6, a non-specific lipid transfer protein type 2 (a small, durable plant protein that survives heat and digestion) found in celery tuber. IgE antibodies are the type your immune system makes when it becomes primed to react to a substance, in this case, a specific celery molecule.

A positive result means your immune system has produced antibodies that recognize this particular celery protein. This is called sensitization. Sensitization is not the same as a guaranteed allergic reaction, but it is the immunological starting point for one.

Why Component Testing Matters

Standard celery allergy tests use whole celery extract, which contains a mixture of proteins. Component testing breaks this apart and looks at individual molecules one at a time, including PR-10 proteins (a family of plant proteins linked to birch pollen cross-reactivity, such as Api g 1), profilins (small cytoskeletal proteins like Api g 4), high-molecular-weight glycoproteins (such as Api g 5, whose IgE binding is driven by cross-reactive carbohydrate determinants), defensin-linked proteins (such as Api g 7, homologous to the major mugwort pollen allergen Art v 1), and non-specific lipid transfer proteins (which include both Api g 2, a type 1 lipid transfer protein from celery stalks, and Api g 6, a type 2 lipid transfer protein from celery tuber).

The reason this matters: different protein families carry different clinical meanings. Reactivity to PR-10 proteins often means mild, localized symptoms tied to birch pollen season. Reactivity to defensin-linked proteins like Api g 7 is associated with mugwort pollen cross-reactivity and, in some cohorts, severe reactions. Reactivity to lipid transfer proteins is the family most often linked to systemic reactions in Mediterranean populations. Importantly, Api g 2 (type 1) and Api g 6 (type 2) are immunologically distinct, with limited cross-reactivity between them, so results for one cannot be assumed to predict results for the other.

What the Evidence Says About Api g 6 Specifically

Api g 6 was first characterized by Vejvar and colleagues in 2013, who reported IgE reactivity to Api g 6 in roughly 38% of celery-allergic patients tested, establishing it as a meaningful but less-studied celery allergen. In a Swiss study of celery-allergic patients by Ballmer-Weber and colleagues, a combination of Api g 1.01, 1.02, 4, 5, and 7 reached high sensitivity for diagnosing celery allergy, while the lipid transfer proteins Api g 2 and Api g 6 were described as 'not relevant' in that population. In that cohort, the strongest link to severe anaphylaxis was sensitization to Api g 7, not to Api g 6.

In a separate Italian study of defensin-sensitized patients, Api g 7 was the dominant sensitizer, while the lipid transfer proteins Api g 2 and Api g 6 were detected in a minority of patients. In that cohort, lipid transfer protein sensitization, specifically to Api g 2, was strongly associated with severe systemic reactions; Api g 6 was not separately quantified as an independent risk marker, and the original characterization work found only limited cross-reactivity between Api g 2 and Api g 6.

Severe Reaction Risk

The lipid transfer protein family that includes Api g 6 matters clinically because these proteins are unusually stable. Api g 6 itself has been shown to remain folded at temperatures above 90°C and to resist gastrointestinal digestion, which means it can reach the bloodstream intact and trigger reactions throughout the body rather than just in the mouth. In Mediterranean populations especially, lipid transfer protein sensitization has been linked to systemic reactions, including anaphylaxis.

That said, the available human data have not isolated Api g 6 as an independent risk marker. The clearest signal in current studies is that Api g 2 sensitization is strongly associated with severe systemic reactions, and because Api g 2 (type 1) and Api g 6 (type 2) show limited cross-reactivity, those Api g 2 findings cannot be directly extrapolated to Api g 6.

Cross-Reactivity With Other Foods

Lipid transfer proteins are common across many plant foods, including peach, hazelnut, walnut, peanut, and others. People with sensitization to lipid transfer proteins from one source often react to lipid transfer proteins from unrelated plants. Most of this cross-reactivity evidence concerns type 1 lipid transfer proteins; a positive Api g 6 (type 2) result can still be one signal in a broader pattern of lipid transfer protein sensitization, which is why this test is usually interpreted alongside other component tests rather than in isolation.

Why a Single Reading Is Not the Whole Story

A single positive Api g 6 result tells you about sensitization, not severity. The clinical meaning of your number depends heavily on context: your symptoms, your exposure pattern, your other component results, and whether you live in a region where lipid transfer protein syndromes are common. Without that context, the number alone cannot predict whether you will react, how severely, or to what.

Sensitization patterns can also shift over years as new exposures occur. If you are managing a suspected food allergy or tracking sensitization in a season-dependent pattern, retesting after a year, or sooner if symptoms change, gives you a fuller picture than a one-time snapshot. Retest sooner if you experience a new reaction, start an immunotherapy program, or move to a region with a different pollen profile.

When Results Can Be Misleading

A few realities to keep in mind when interpreting an Api g 6 result:

• Sensitization is not allergy: a positive IgE result means your immune system recognizes the protein, not that you will definitely have a reaction when you eat celery.
• Api g 6 is distinct from Api g 2: although both are lipid transfer proteins, they belong to different subfamilies (type 2 and type 1) with limited cross-reactivity, so an isolated Api g 6 positive result has less well-defined clinical weight than an Api g 2 positive.
• Geographic context matters: lipid transfer protein syndromes are most studied in Mediterranean populations, and the clinical meaning of a positive result in other regions may differ.
• Negative does not rule out celery allergy: a negative Api g 6 does not exclude allergy to celery driven by other components like Api g 1, Api g 4, Api g 5, or Api g 7.

What To Do With an Unexpected Result

A positive Api g 6 result is most actionable when read alongside a broader celery component panel and your clinical history. If you test positive and you have had any reactions to celery, raw or cooked, getting the full set of celery components (Api g 1, 2, 4, 5, 7) gives you a clearer picture of which protein family is driving the response. Pollen component testing for mugwort (Art v 1, Art v 3) and birch (Bet v 1) is often added to map cross-reactivity.

Anyone with a positive lipid transfer protein result and a history of reactions, especially systemic ones, should consider a referral to an allergist for risk stratification and emergency planning. Conversely, a positive Api g 6 in someone with no symptoms and no other lipid transfer protein sensitization is best treated as information to monitor rather than a reason to restrict diet.