Allergy Test Lab Referral Is Even More Problematic

We’ve already discussed how referring patients out for testing by an allergist can be problematic for both the referred patient and the referring clinic. As explained in discussing how referral is a problematic approach to allergy, referrals generally have two destinations: an immunologist (allergy specialist) to handle the condition completely, or a lab for blood testing alone. Either way, referral is illogical, invites the patient not to return to the primary care clinic, forgoes substantial revenue, often costs the patient extra, and implies that most patients who need it never get tested, or even referred, at all. All that is plenty reason enough for primary care clinics to conduct allergy testing in-house, but if that takes the form of ordering a blood test, there’s even greater downside. First, the test mechanics and cost typically mean the lab test is far less comprehensive. Second, in most cases the testing patients get is different, like apples and oranges, and in-house is better. Third, then what? If the lab test detects allergies, the clinic can only offer avoidance as treatment, or really, lack of treatment. With very limited exceptions, there is nothing a lab, or referring clinic, can do to alleviate patients’ symptoms without relocating or other big life changes.

Start with the baseline understanding of in-clinic skin scratch allergy testing. Right there in the primary care clinic it takes perhaps five minutes to prep the patient, then a fifteen minute wait while results develop, then a few more minutes to record the results. That’s it. An MA can do the whole thing (under legally adequate supervision, of course). This 90 second video demonstrates the process well.

Blood testing is only a secondary, expensive substitute for the gold standard skin scratch test.

The American College of Allergy, Asthma & Immunology states plainly: “Allergy skin testing is the gold standard and is used along with the medical history to find out exactly what things a person is allergic to." Medical history includes symptoms experienced, and how often. That’s why the patient symptom survey is so crucial as a screening tool. The ACAAI published that conclusion years ago and has never wavered from it. It goes on: “Skin testing is the preferred method used by trained allergists, and is usually the most accurate. Blood tests may be ordered in specific situations.” The method preferred by allergists ought to be preferred by primary care physicians as well, and it’s not as though it takes a specially trained scientist with years of experience to properly use a ruler. That’s all it takes to measure a wheal, meaning a bump or welt resulting from a skin scratch exposure to a bit of allergen. Determining the size of that wheal relative to control wheal, in turn, is pretty much all it takes to diagnose allergy. That measurement is even easier when the ruler is specifically adapted to the task. So, because skin testing is the gold standard, and most accurate, blood testing is a lesser choice even before cost comes into the equation.

Then considering cost, which is obviously very important and unavoidable, AAAAI observes that “Skin tests give fast result and usually cost less than allergy blood tests,” too. That’s especially true when compared allergen-for-allergen, or in CMS reimbursement terms, unit for unit. The cost discrepancy, which is vast, at least partially results from the typical, limited capacity of blood testing analyzers (machines), as compared to the ease of placing plastic applicators on the skin as shown in the video, all in one go. The machines usually need to be run several times to accommodate tests for up to 78 or more allergens. Thus, in June 2026 published pricing for testing even just one allergen, such as cat or dog dander, is more than $40, and for multiple-allergen tests such as 18 trees, weeds, molds, and animals, the cost was $215. Those prices are from a bulk reseller of tests by two of the largest national labs. At that bulk rate, blood testing for 78 allergens as in MRS Allergy’s 80 panel would be pushing $1,000.

Blood tests are typically (far) more expensive than skin prick tests

First, what’s a blood test, really. The most commonly used blood test for allergy is a fluoroenzyme immunoassay (FEIA) that relies on a hydrophilic spongy polymer that has allergens or their components bound to its large, exposed, internal surface area. IgE antibodies from the blood sample that are specific to those allergens bind to them, then labeled anti-IgE antibodies bind to the patient’s antibodies. A fluorescent substrate applied to the anti-IgE antibodies produces a quantifiable signal proportionate to the amount of bound IgE, indicating allergies. Clinically, the test results should be compared to the patient’s medical history, which calls for cataloging symptoms experienced in a systematic way: a patient symptom survey again.

Compared to using a piece of plastic to put a bit of allergen just under the surface of a patient’s skin and watching what happens, such complex chemistry and quantification is quite expensive. To give an idea of just how expensive, a 2016 Health Technology Assessment by the National Institute for Health Research (DOI 10.3310/hta20670, apx. 7) found that for the same “no. of allergens tested per person” the material “costs per patient tested” of an “IgE test” was well over an order of magnitude (10x) higher than the cost of a “SPT,” meaning skin prick test.

Blood tests are typically regional, not national.

In light of the greatly higher expense per allergen tested, it stands to reason that IgE tests would be less comprehensive than skin prick testing, assuming the same expenditure. One potential upshot of that observation is that published catalogs indicate the two largest labs do not offer an 80 panel. Instead, they offer panels of typically fewer than 30 allergens that are tuned, slightly, to represent the allergens from different regions of the country. There are twenty such regions, with Alaska, Hawaii, and Puerto Rico representing one region each, the rest composed of groups of states or parts of them. California is part of four regions, for instance, while the Dakotas, Nebraska and Kansas comprise a single region of four states. The accompanying map shows all 20 regions for reference. Those regions’ boundaries and the allergens chosen for each region are reportedly based on a proprietary system created by an IgE test supplier. An 80 panel that comprehensive would need to be assembled from one of the regional bundles plus individual allergens, skyrocketing costs.

Blood tests are typically (far) less comprehensive than skin prick tests

In practice, the cost advantage often translates to skin prick testing being more comprehensive. To illustrate, the largest national labs offer regional panels maxing out below 30 allergens while skin prick test panels, such as MRS Allergy’s national 80 panel, often test for substantially more than double the number of allergens for lower cost. Again, at some level likely related to the large expense of more comprehensive tests, the tests the two largest national labs offer for each region max out at 27, though “reflexes” (allergen components) can be seen to increase that number somewhat. The accompanying graphic is a visual comparison of the difference in comprehensiveness. The blue diamonds indicate allergens that may be included in an 80 panel, or in this instance, that are in fact included in MRS Allergy’s standard 80 panel. Call that the baseline. The narrow green area at the bottom shows where both national labs include those baseline allergens in each of their regional tests. The yellow areas indicate where the labs test for baseline allergens in some regions, but not all of them. For example the labs test for Perennial Grass only in region 12, and for one particular mold only in region 19, whereas the baseline 80 panel skin tests always includes both. The large red area indicates where allergens included in the baseline 80 panel are not included in the national labs’ regional tests at all, anywhere.

Viewed another way, there are more than 40 total allergens, but fewer than 30 in each regional test, and the regional selections are characterized by a core group of about a quarter of the total, then categories of decreasing usage. About ten allergens are common to all 19 tests (or 20, if the national lab offers a Hawaii panel). Use of roughly fourteen more is fairly widely distributed, common to at least half the regions but not all of them. Ten more allergens are only used in four to eight regions, and the rest are used in only three regions at most. Of those, six allergens are unique to a single region each. Nearby is a graphic representation of this allergen distribution by regional test. The thickness of the bands indicates how many regions each allergen, represented by a circle, is used in: thicker band means more regions. Hover over the allergen circle to display the regions where it’s included in one of the national lab’s regional test according to its published catalog.

Baseline, Exceptions, Cross-Reactivity, and Primary Care Physician Judgment

There’s one last wrinkle in the regional testing allergen selection regime: allergens included in regional IgE panels by the national labs but not included in the national skin test baseline represented by the MRS 80 panel. Of those there are fewer than ten. One of them is American elm. That’s a story all by itself. Another is a mold called blomia tropicalis which is highly allergenic but also extremely limited in geographical presence, occurring only in the southern portion of Florida. The rest are likewise restricted to limited geographies, such as mimosa/acacia pollen present only in the Sonoran Desert areas in adjacent corners of California and Arizona.

These differences in allergen panels are artifacts of economics and practicality. Economics, as discussed above, limit the number of allergens in an IgE test. Practicality limits the number of allergens in a skin test. There’s a limit to how many allergens you can reasonably place on a patient at one time. Eighty is plenty, the thinking goes. And yet, there are far, far more than 80 allergens available as test serums. Consequently, some allergens have to be excluded.

National skin test panels such as the MRS 80 Panel make those decisions on the basis of prevalence, of two kinds. First, how prevalent is the allergen across the country? The more common it is, the greater the weight in favor of including it. Second, how many people are actually allergic to it? The more there are, the more weight in favor of including it. Those weights are also adjusted based on cross-reactivity—the idea that another, related allergen might trigger allergic reaction. Mouse epithelium and mouse urine, for instance, are so likely to trigger the same reaction that in the allergen table nearby, they’re treated as equivalents. Allergen sets like apple and birch pollen, or latex and avocados, are cross-reactive but simultaneously (and perhaps intuitively obviously) sufficiently distinct as to warrant separate assessments.

The mathematical conclusions from such analysis are not necessarily obvious. The South Florida mold, blomia tropicalis, exists among the population of South Florida, and that population is huge. Mimosa/acacia pollen is present in Phoenix, the fifth largest metro area population in the USA. Judgment calls are accordingly required in assembling these panels. Where primary care physicians’ judgments differ, additional allergens can be added easily, with or without substituting another allergen out.

Regionality and comprehensiveness have ramifications for treatment

The national labs’ allergen distribution and regional test regime, while very much less comprehensive than the national baseline skin test allergen set, is at least arguably adequate to whatever extent it catches most allergies for most people, but given price differential, skin testing for the same panels would be more cost efficient. A more important and more common problem is the failure to detect patients who would benefit from allergy testing in the first place, which counter-indicates the referral method and cries out instead for in-house deployment of the patient symptom survey as a regular screening tool and to accompany any and all allergy test results as the pertinent medical history. Further still, regional testing and treatment work best only if you don’t leave where you live. If you travel or relocate to another region, however, it can be a problem. Also, some of the allergen choices, such as American Elm, are questionable.

Finally, perhaps it’s obvious that the more comprehensive an allergy test is, the more comprehensive the treatment is likely to be. Likewise, if you’re treated to suppress reaction to allergens that are localized to a particular region, you’re liable to react again once you encounter allergens that are common only to other regions. To illustrate by reference to the stoplight chart, a patient tested and treated in Kansas (region 9) could still be allergically reactive to rough marshelder weed pollen, which isn’t on the region 9 panel, then have issues if she moves to a neighboring state like Missouri (region 8) or Oklahoma (region 10), where it is.