The Elm Story: Ubiquity, Allergenicity, Availability, and Cross-Reactivity

The selection of elm pollens is a highly instructive distinction between the national and regional test panels. For clinics evaluating allergy testing in primary care, it also shows why panel design matters. Keen readers will note that American elm is in every regional panel except Alaska and Hawaii, but is absent from the national 80 panel. Instead, the national panel includes both Chinese and cedar elm, which are both absent from the regional panels. Why?

Considerations for Assembling a Test Panel

Exploring the distinction provides valuable insight into optimizing allergen selection. Deepening understanding in this area doesn’t require extremely technical knowledge. There’s no need to delve into heady concepts like epitopes, avidity, protein morphology, or measurement methods and units few have ever heard of, like 75 kiloDalton protein bands. For present purposes it will suffice to understand the conclusions scientists have drawn from the technical evidence.

Thus, after a bit of thought, it’s pretty intuitive that allergy test optimization must consider how common and potent an allergen actually is, and what it may indicate about other, adjacent allergens. In only slightly more technical terms, geographic prevalence combined with local density matters, along with how many people are how allergic to it. That is one reason point-of-care allergy testing needs more than a generic list of allergens: the panel has to make clinical sense for the patients a practice actually sees.

• A weed or tree that’s present all over the country, but only in vanishingly small numbers, may be less important for testing than one that’s absent from large parts of the country, but where it is present, is all over the place.
• An allergy to pollen A may be more diagnostically important than an allergy to pollen B if pollen A allergy also suggests strong allergies to ten other common pollens, and pollen B allergy doesn’t. Pollen A is said to be highly cross-reactive, while pollen B isn’t.
• Allergen X, a weed or animal that’s all over the place in high numbers, may be less important for testing than a comparatively rare one, allergen Y, if loads of people are strongly allergic to the rare allergen Y and almost no one is allergic to the common allergen X. That’s called allergenicity, with allergy Y being more highly allergenic than allergen X.

And, crucially in this case, it’ll be obvious that all that analysis is only relevant if the pollen in question is available as a test serum. Any reasonably priced test requires allergen in commercially available, commercially reliable, quantities. No allergen, no test, no treatment, even if people commonly suffer badly from the allergy.

Elm Selection

So, elm pollen: consider this interactive prevalence map. Click the buttons at the top to see the rarity or abundance of the three different kinds of elm pollens across the states. You’ll find that American elm is completely absent in the mountain and Pacific west, save for Colorado, and also isn’t in Alaska, Puerto Rico, or Hawaii. Chinese elm, on the other hand, is everywhere in the lower 48 states, and also Hawaii.

From a geographic prevalence standpoint, therefore, if you had to choose only one then Chinese elm is obviously the better one to test nationally, instead of including American elm in multiple regions where it doesn’t grow. It’s quite curious why the national labs’ regional tests include American elm that way, and Chinese elm not at all.

But the national panel doesn’t include just one elm; it includes cedar elm as well as Chinese. If American elm is deprioritized in part because it’s not present in a third of the country, why include cedar elm which is even less geographically present?

First, because of cross-reactivity. Testing for Chinese and cedar captures the vast majority of American elm allergies. That is, while elm allergenicity as a whole hasn’t been studied as thoroughly as some other allergens, it is known to be substantial, and also believed that by including both Chinese and cedar elm, the test is more likely to detect American elm allergies than if only one of Chinese elm or cedar elm were included. The Venn diagram illustrates the overlap, though it’s only conceptual; areas should not be taken to represent clinical data.

Second, because of availability. American elm is more susceptible to a blight called Dutch elm disease which has progressively devastated American elm populations over the past century. Fewer living American elm trees means less pollen available to harvest which threatens commercial availability of that allergen considerably more than Chinese or cedar elm. In fact, a 2025 paper in the Annals of Allergy Asthma & Immunology characterized American elm as a “vanishing allergen” that’s resulting in a “crisis … in allergy treatment.” (Peterson et al, PMID: 40194764 DOI: 10.1016/j.anai.2025.04.001). Including American elm in any panel thus threatens reliable long term availability of that panel substantially more than leaving it out would. Thus, by including Chinese and cedar elm but not American elm, the national panel helps to ensure reliably available testing and treatment serums while limiting the potentially missed allergies to the reactivity sliver in the American elm exclusive area of the diagram, inside the red dashed line.

The Ultimate Consideration: Medical Judgment

As noted earlier, reasonable medical practitioners could reach different, justifiable conclusions about allergen selections. Well, perhaps excepting inclusion American elm in multiple regions where it doesn’t exist to the exclusion of any other kind of elm that really is there—that’s a bit of a headscratcher. Toward that end, substitutions, national panel, or additions, national labs, can be made.

That medical judgment is also why allergy testing should not be treated as a disconnected lab transaction. Primary care teams already see the patient history, symptom patterns, geography, and follow-up needs that make allergen selection meaningful. For practices comparing care models, the distinction between in-clinic allergy testing vs lab referral becomes especially important.

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Peterson RL et al. Vanishing allergen: Addressing the crisis of American elm pollen extracts in allergy treatment. Annals of Allergy, Asthma & Immunology. 2025. PMID: 40194764. DOI: 10.1016/j.anai.2025.04.001

Ahlroth M et al. Cross-reactivity between American and Cedar elm: identification of a 75 kDa shared protein band. Journal of Allergy and Clinical Immunology. 2008. [Molecular basis for Cedar/American elm cross-reactivity referenced in cross-reactivity diagram.]

Dispenza MC et al. Tree pollen allergen sensitization: prevalence, risk factors, and geographic variation in the United States. JACI Global. 2026. PMC12914427

American Elm Shortage Impacts Practices. American Academy of Otolaryngic Allergy member alert. aaoallergy.org/american-elm-shortage

Allergen of the Month — Chinese Elm (Ulmus parvifolia). Annals of Allergy, Asthma & Immunology. 2014. annallergy.org

ImmunoCAP t8 Elm (Ulmus americana). Thermo Fisher Scientific / Phadia allergen encyclopedia. thermofisher.com

ImmunoCAP t45 Cedar Elm (Ulmus crassifolia). Thermo Fisher Scientific / Phadia allergen encyclopedia. thermofisher.com

Regional Respiratory Panel — Region X (Oklahoma, Texas). Quest Diagnostics. questdiagnostics.com