Alder (Aln g 1) IgE Test · Blood

If your eyes water, your nose runs, or your throat itches in early spring, alder pollen is one of the first culprits worth investigating. This test measures your immune system's IgE (immunoglobulin E, an antibody) response to a single, well-defined protein in alder pollen called Aln g 1, the alder PR-10 (a family of plant defense proteins) major allergen. It gives you a molecular-level answer about whether your symptoms are tied to alder specifically, or to a broader family of related tree pollens.

It also reveals something a standard whole-pollen extract test cannot. Because Aln g 1 belongs to the same protein family as birch Bet v 1 and hazel Cor a 1, a positive result often points to a shared sensitization pattern across multiple trees, and sometimes to certain raw fruits and nuts that share the same protein shape.

What This Test Actually Measures

Aln g 1 (the major alder pollen allergen) is a PR-10 protein, meaning it is a plant defense protein with a shape that closely resembles allergens in birch, hazel, beech, and oak pollen. When your immune system mistakes this protein for a threat, it produces IgE antibodies tuned to recognize it. Those antibodies circulate in your blood and sit on immune cells, ready to release histamine and other chemicals the next time you breathe in alder pollen.

This blood test measures the amount of IgE antibodies in your blood that are specifically tuned to Aln g 1, as opposed to total IgE (which sums every IgE in your blood, allergy-related or not) or whole alder extract IgE (which mixes many alder proteins together). Multiplex platforms used in research, including microarrays and the ALEX2 Allergy Explorer, can measure Aln g 1 alongside dozens of other component allergens from a single blood draw. Capillary fingerstick samples and venous blood samples have shown very high agreement for Aln g 1 (correlation of 0.98), so either source can give a reliable reading.

Why You Should Care About Alder Specifically

Alder trees release pollen earlier than most allergens in the temperate spring, often before birch. If you suspect tree pollen allergy but symptoms start surprisingly early in the season, alder is a likely driver. A direct measurement of Aln g 1 IgE tells you whether your body is primed to react when those first pollen grains hit the air.

In adults with atopic dermatitis (eczema with an allergic component) tested on the ALEX2 multiplex platform, Aln g 1 was among 18 component allergens showing high or very high specific IgE in 75% of participants. In a German cohort of adults with seasonal allergic rhinitis, roughly 45% had detectable IgE to Aln g 1. So the marker is common enough to matter for a broad slice of people with respiratory or skin allergies, not just those who already know they react to trees.

Cross-Reactivity With Birch and Other Trees

This is the single most useful concept for interpreting your result. Aln g 1 shares so much structural similarity with birch Bet v 1 and hazel Cor a 1 that IgE made against one often binds the others. In one classic study, 95% of tree-pollen-allergic patients had IgE patterns compatible with birch as the primary sensitizer, with the alder and hazel reactions explained by cross-recognition rather than independent allergy. Specific IgE to alder pollen (measured by an older extract-based method) tracked extremely closely with birch IgE, with a correlation coefficient of 0.97 (a near-perfect match).

What this means for you: a positive Aln g 1 result rarely points to an isolated alder problem. It usually signals broader sensitization to the entire Fagales tree pollen family (alder, birch, hazel, hornbeam, beech, oak). Testing Aln g 1 alongside Bet v 1 and Cor a 1 can clarify whether birch is the primary driver and alder is along for the ride, or whether your reactivity spans several trees independently.

Pollen Food Allergy Syndrome

PR-10 proteins like Aln g 1 are not only found in tree pollen. Cousin versions appear in apples, pears, cherries, peaches, hazelnuts, almonds, carrots, celery, and soybeans. If your immune system has learned to recognize the PR-10 shape from pollen, it can also react when you eat raw versions of these foods, producing the itching mouth, tingling throat, or swollen lips of pollen food allergy syndrome (also called oral allergy syndrome).

In a study of 600 Japanese children and adolescents, those with higher alder-specific IgE had a markedly increased risk of pollen food allergy syndrome. Alder sensitization carried an odds ratio of 6.20 for developing the condition, meaning sensitized individuals were about six times as likely to experience food-pollen cross-reactions as those without alder sensitization. The more pollens someone was sensitized to, and the higher the IgE levels, the greater the risk.

Atopic Dermatitis and Broader Allergic Disease

Aln g 1 IgE rarely travels alone. In the 100-patient atopic dermatitis study mentioned above, high IgE to Aln g 1 sat within a wider profile of PR-10 sensitization that was linked to more severe skin disease and a higher rate of co-occurring asthma and allergic rhinitis. The researchers did not single out Aln g 1 as an independent driver of severity, but the overall pattern of strong, multi-component IgE was a marker of more complex allergic disease.

In a German birth cohort study, airborne PR-10 IgE including Aln g 1 was a hallmark of the persistent atopic pattern in children, in contrast to weak, transient food-only PR-10 responses seen in non-atopic kids. Early, strong IgE to airborne PR-10 proteins like Aln g 1 may signal a trajectory toward ongoing allergic disease rather than a passing childhood reaction.

What This Result Doesn't Tell You

A positive specific IgE result confirms sensitization, which is your immune system's readiness to react. It does not, by itself, diagnose a clinical allergy. Some people have measurable Aln g 1 IgE in their blood without ever developing symptoms during alder pollen season. The link between a blood result and real-world symptoms is strongest when the lab finding lines up with what your body actually does during exposure.

Higher IgE levels generally suggest a higher likelihood of clinical reactivity, but no single number tells you whether a specific exposure will trigger an attack. The most useful interpretation pairs your IgE pattern with your symptom history and pollen calendar.

Tracking Your Trend

A single Aln g 1 IgE reading captures your immune system at one moment. Allergen-specific IgE levels can drift over months and years as exposure changes, immunotherapy progresses, or general allergic disease evolves. Tracking your number over time gives you something a one-off reading cannot: a trajectory.

Get a baseline reading. If you are starting allergen immunotherapy aimed at tree pollens, or making major changes in pollen exposure (moving to a different climate, planting or removing alder trees nearby), retest in 6 to 12 months to see how your sensitization is moving. Otherwise, at least annual monitoring during periods of active allergic disease gives you data to act on. A meaningful change over time is more informative than crossing or staying below any particular cutoff.

What to Do With an Unexpected Result

If Aln g 1 IgE comes back elevated and your symptoms make sense, the natural next step is broader component-resolved testing of related tree pollens (Bet v 1 for birch, Cor a 1 for hazel) to map your full Fagales sensitization. If you have unexplained mouth itching or throat tingling with raw apples, peaches, hazelnuts, or carrots, the Aln g 1 result helps explain it and points to pollen food allergy syndrome rather than a primary food allergy.

If your IgE is elevated but you have never had symptoms, that is sensitization without clinical allergy. It is worth knowing your baseline, especially heading into spring pollen season, but it does not require treatment on its own. An allergist or immunologist can integrate your result with skin testing and your symptom history to decide whether immunotherapy or symptomatic medication is worth pursuing. If your IgE is low but you still react badly during alder season, a skin prick test or repeat blood test on a different platform can help reconcile the discrepancy.

When Results Can Be Misleading

A few factors can distort an Aln g 1 IgE reading or its interpretation:

• Cross-reactivity confounding: a positive Aln g 1 result can be driven by primary birch sensitization rather than an independent alder allergy. Without testing Bet v 1 in parallel, you may misattribute symptoms.
• Sensitization without symptoms: detectable IgE in blood does not always mean you will react to alder pollen during pollen season. The lab value is one piece of the picture, not the whole diagnosis.
• Assay differences between labs: specific IgE numbers from different platforms (ImmunoCAP, ISAC, ALEX2) are not perfectly interchangeable. Compare serial results on the same platform whenever possible.
• Total IgE skew: a very high total IgE (from eczema or parasitic infection) can produce non-specific signal on some assays. Interpreting a single allergen result without context can overestimate the importance of any one number.