College of American Pathologists
Printable Version

  Lab-based allergy testing on
  the march


cap today

April 2002
Cover Story

Karen Titus

A little knowledge can be a dangerous thing. In the case of allergy testing, however, it may be just enough.

Or too much.

Then again, a lick of learning may not cut it. Or, if it does, it may not matter. Such is the state of in vitro allergy testing these days.

The easiest thing to say about allergy testing is that it’s nothing to sneeze at. Then it starts to get tricky.

Some of the long-standing debates, to be sure, are starting to fizzle out. Though long considered to be less sensitive than skin testing, in vi-tro allergy testing has made great strides in recent years, and plenty of experts suggest the best serological tests offer performance characteristics that are equivalent to skin tests.

"I’m comfortable with that," says Rob Reinhardt, MD, medical affairs director for Pharmacia Diagnostics’ U.S. operations, and a family physician who still practices part time.

"If one is concerned about sensitivity to inhaled allergens and certain other types of allergens, the two methods are pretty much comparable," says Henry Homburger, MD, a consultant in laboratory medicine and director of the Immunology Antibody Laboratory at Mayo Clinic.

Some even suggest that in vitro tests may have a leg up on certain skin tests because they often use standardized allergen extracts—not always the case with skin tests. There’s no standardized skin test extract for latex allergy in the United States, for example, but there is one for its in vitro counterpart, says Hendrik Nolte, MD, PhD, who has an assistant professorship at the University of Copenhagen, Denmark, and a private allergy practice in Avon, Conn. The same is true, he says, for some of the most common allergens, including dust mites, certain grass pollens, and danders and tree pollens, as well as some food, drug, and venom allergens.

"If you’re an advanced allergist," Dr. Nolte says, "you are aware of the fact that certain skin testing extracts are not optimally manufactured."

All of which appears to leave the door wide open for laboratories wanting a piece of the action.

There are compelling reasons for laboratories to do allergy testing. Russell Tomar, MD, who chairs the CAP Diagnostic Immunology Resource Committee, suggests pathologists who don’t do it may be missing the boat. Allergy testing offers "an opportunity to improve services and increase profits," he says.

New knowledge about how allergic diseases develop bolsters that argument. Those who are likely to develop allergies become progressively sensitized to different types of allergens, beginning with food in early childhood, then progressing to dust mites and the more conventional inhalant allergens, like pollen, later on in childhood—the so-called allergy march.

Identifying allergies relatively early on could help phy-sicians moderate allergy development throughout patients’ lives. "The only way primary care physicians have of doing that is in the in vitro test," says Dr. Homburger.

"This has profound implications for how clinicians go about doing this testing," says Dr. Homburger, who notes it’s relatively ineffective to test for a whole host of allergens in very young children; in this same age group, testing for food allergies is critical.

As children grow older, it’s more important to test for conventional inhalants, such as dust mites and mold—"the sorts of things that can produce rhinitis and asthma in what you might call middle-aged children, between 6 or 7 and the early teen years," says Dr. Homburger.

Betts Carpenter, MD, PhD, observes that allergy often goes unrecognized in children with chronic otitis media. "A lot of times, the underlying cause is allergy," says Dr. Carpenter, professor and vice chair of the Department of Pathology, Marshall University School of Medicine, Huntington, W. Va. Moreover, she says, many food allergies present in children progress to asthma if left undetected. Earlier testing "could have an impact on preventing later asthma in children."

Many point to the ETAC studies (Early Treatment of the Atopic Child), published in the late 1990s in the pediatric allergy and immunology journals. The studies looked at young children with atopic dermatitis, and the likelihood that they would develop asthma. Children who tested positive for the presence of allergen-specific IgE antibodies were treated with antihistamines, which reduced either their likelihood of developing asthma or the severity of the disease.

"Asthma definitely fits into this," says Dr. Reinhardt. "A substantial percentage of asthmatics are atopic, and you can’t adequately control their asthma unless you control the atopic part of the equation."

Dr. Homburger also points to a study published in the March 2002 issue of The Journal of Allergy and Clinical Immunology (Vol. 109, No. 3), a large epidemiologic investigation of patients with allergic rhinitis. The data show convincingly that allergic rhinitis predisposes—as an independent risk factor—to the development of asthma in adult life, he says. "Obviously, one cannot hope to prevent such downstream consequences if one does not first recognize who has allergic rhinitis and who does not," Dr. Homburger says. "This is the medical rationale for in vitro testing, since most patients with rhinitis are not managed by allergists unless the disease is first recognized by primary care physicians."

On the flip side, mounting evidence suggests many patients with upper respiratory symptoms—perhaps up to 60 percent—are being treated with antihistamines, nasal steroids, and other allergy medications even though they don’t have allergies. Allergy testing is just as important for ruling out allergic disease, especially during visits to primary care physicians. "Many diseases can give the appearance of an allergic disease," Dr. Homburger says.

Even targeted treatment may not be enough. "Allergy is a fairly common disease. A lot of physicians deal with it by prescribing symptomatic relief," says Jay Weiss, PhD, director of immunoassay development at Esoterix, a national laboratory services company that performs in vitro allergy testing. "So they may never identify what you’re allergic to, and you may never know if there’s any sort of disease progression."

Other recent studies indicate that quantitative measurements of specific IgE to certain foods correlate to the risk of having severe allergic reactions, such as anaphylaxis, says Dr. Nolte. "That has been demonstrated with milk, peanut, and egg, and perhaps soy," he says. "In those instances, it may be possible to use specific IgE absolute values to predict whether the patient will have a more severe reaction."

Outside of that, little published literature shows that allergy testing is predictive. "But there haven’t been a lot of studies done in that area, and I think it’s open for that sort of investigation," Dr. Weiss says.

In Dr. Weiss’ view, allergy testing is underused. "It’s only being used in treatment; it’s not being thought of as a way to prepare for potential disease, as a means for changing behavior so future disease may not arise or become severe."

There is another reason for laboratories to offer in vitro allergy testing—simply put, because they can.

In the past, in vitro allergy testing was labor intensive and needed the guidance of experts, if not a guru. "Up until now, you needed specialized equipment in your lab to be able to run allergy testing, and you had to have one or two techs trained to do the test," says Debra Hovanec-Burns, PhD, director of product support--allergy and infectious disease for -Diagnostic Products Corp., which recently added allergy testing to its Immulite 2000 immunoassay analyzer.

As tests become automated and able to be run on broader platforms, specialized knowledge may become less critical. "Software may be able to incorporate some of that understanding into an instrument," suggests Dr. Weiss.

Guided in part by a 1997 NCCLS document, "Evaluation Methods and Analytical Performance Characteristics of Immunological Assays for Human Immunoglobulin E (IgE) Antibodies of Defined Allergen Specificities" (I/LA20-A, Vol. 17, No. 24), manufacturers have largely put themselves on the same page in terms of standardization and variability. The document was written as much for manufacturers as it was for labs, says Dr. Homburger, one of the authors.

Has the document had the desired effect? "I would say a qualified ’yes,’" says Robert Hamilton, PhD, professor of medicine and pathology, Johns Hopkins University School of Medicine, and another of the document’s authors. The qualification: By the time the guidelines were established, the second-generation methods that are now commercially available were already in place. But no new subsequent assays have been developed, he says, and the number of older, poorly performing assays has dropped, "which suggests the field is moving in the right direction." The document has also helped define quality control guidelines for IgE antibody assays, he says, and served to educate CLIA inspectors unfamiliar with the intricacies of serum IgE antibody testing.

The better methods on the market "perform remarkably well," he adds.

Dr. Homburger agrees. "I think the manufacturers have done quite a good job. There are some really good ones out there," he says, though he tiptoes around the little matter of naming names. "I don’t want to mention particular manufacturers, because there are some real differences."

At last count, there were some 15 different FDA-cleared assay formats available, with clinical laboratories offering their own home-brew assays as well. "There’s a real spectrum out there," says Marshall’s Dr. Carpenter. Not surprisingly, the manufacturers are adept at arguing the strengths of their respective systems.

One commonly cited difference is the matrix used to absorb the antigen. A larger surface area binds more protein, which, in theory, enhances sensitivity, says Dr. Nolte, whose laboratory in Copenhagen runs several different in vitro assays. Matrices with less surface area—so-called two-dimensional systems—would, theoretically, be less sensitive. "But the differences in sensitivity are marginal," he contends. Other differences are evident in the tests’ calibration ranges and size of the solid-phase mass.

Some discrepancies between assays are linked to disparities in the reagents used, rather than technical differences between the assays. "When you compare the assays for the standardized and well-characterized allergens—the tree pollens, some of the grass pollens, and the dust mites—the variation is minor, because everyone is basically using the same extracts," says Dr. Nolte. For foods and some of the more esoteric allergens, however, huge variances occur because the reagents differ. "That’s because the extract and protein profile in these extracts all differ," he says.

Food allergens are difficult to standardize, agrees Emi Zychlinsky, PhD. That’s because of the many proteins involved and their vulnerability to enzymes. "If you’re not careful with your extract, the important proteins are going to be broken down," says Dr. Zychlinsky, director of research and development, Hitachi Chemical Diagnostics; the company has an in vitro test with a panel approach for simultaneous testing of several allergens with one patient sample.

The biological variability of the allergen materials is the biggest obstacle to overcoming calibration problems, according to Dr. Weiss.

"The allergen materials continue to be raw materials that we buy from pollen houses or manufacturers of skin testing reagents. And those materials, from lot to lot, from year to year, can be variable," he explains. Even when manufacturers buy materials from the same vendor, he says, "you can’t expect the materials to give the same values."

"These allergen mixtures are so complex," Dr. Weiss continues. Attempting to purify them would enable manufacturers to produce concentrations that more closely match one another. But what would be lost in the process—the diagnostic ability to detect people with specific IgE to the allergen—hardly makes it worthwhile. "Physicians won’t think the assay is worth being done."

Dr. Weiss identifies another important area for normalizing values across manufacturers—primary calibration. Most if not all manufacturers’ assays are calibrated to the WHO second international reference preparation. "We all use the total IgE curve that uses that same reference, so we are using the same material to calibrate our assays," he says. "I think a lot of things have gotten better with in vitro testing because of that."

That’s not to say the tests are all gold medal winners. "Not all methods are equal," Dr. Homburger concedes, who’s seen his share of methods during his 25 years of experience with in vitro allergy testing. "Pathologists who are going to do this testing need to avail themselves of the CAP Survey data and evaluate the different methods."

Nonetheless, the real incongruity may lie with the tests’ applications, rather than their makeup. The tests themselves now appear to be technically within reach of any good laboratory. Says Dr. Homburger: "I’d like to see these tests evolve more in their use than in their technical characteristics. By that I mean a greater awareness on the part of the primary care physicians about the types of sensitivities that develop early in childhood, those that develop later in childhood, and those that may develop in adulthood," he continues. "So that the appropriate tests are ordered at the proper time." This, more than technological advances in the tests, would improve health care, he says.

Simply knowing that good allergy testing methods are available and may be underused doesn’t give laboratories the green light, however.

Dr. Carpenter is an admitted fan of in vitro allergy testing, and her advocacy sounds like a testimonial at times. In her primary workplace, a community hospital laboratory, in vitro allergy testing "is a very easily instituted test," she says. "It’s in the chemistry laboratory, and all the 11 technicians there can easily run it with very little training. The only thing that takes a little bit of time is learning the software, but it’s pretty much a stand-alone assay system."

"We’ve had a tremendous interest among physicians for running this test," she goes on. "We run it every day, and it’s been very, very successful, and very, very easy to institute. We haven’t had any problems with it."

But it’s probably no coincidence that her fellowship was in immunopathology. "I had the background, so it was easy for me when we started doing this testing," she acknowledges. That’s probably not the norm. The majority of pathologists practicing in community hospitals may have as their only exposure to allergy testing a single rotation during their residency. Indeed, Dr. Carpenter says, her colleagues in the laboratory, as well as her primary care colleagues, benefited greatly from the intensive education provided by the system’s vendor, Pharmacia. "They got everybody up to the level we needed to institute the testing," Dr. Carpenter says.

Lawrence Spatz, PhD, a clinical chemist at Berkshire Medical Center, Pittsfield, Mass., is also quite familiar with the benefits of in vitro allergy testing. Reimbursement is good, interest from clinicians is high, and he likes being able to offer the test in-house. "From a service point of view alone, it makes sense to not send it out," he says.

Berkshire has offered allergy testing for a decade. "It hasn’t been hard to maintain this testing," he says. "And now it’s come to the point where many of these tests are no longer sophisticated. Anyone can put them on their machine and do them."

But his lab, like Dr. Carpenter’s, has benefited from a few perks.

Berkshire’s foray into allergy testing was supported by a pathologist with a keen interest in esoteric testing, along with a cadre of well-trained technologists who could do highly sophisticated testing. "We had a good special chemistry department to begin with," Dr. Spatz says. "When we first started doing this, there was a lot of hands-on work, but we had the staff to do it." Berkshire, it should be noted, enjoys its own school of medical technology, so for years the laboratory has been able to hire cream-of-the-crop MTs. "We have a lab that’s staffed almost entirely by licensed, college-educated med techs, and we have very little turnover," Dr. Spatz says.

All helpful, yes. But lacking immunopathology fellowships and a med tech school, should laboratories still consider doing allergy testing?

Having a few facts in hand is definitely in order.

Dr. Weiss starts with a few basics, beginning with the reminder that even though in vivo and in vitro tests are fairly comparable in terms of quality, they’re distinct tests. "People forget that, I think, when they try to compare the two," he says. Laboratories are testing for circulating IgE antibodies, which have a half-life of only two or three days. Skin tests target antibodies that are bound to mast cells in the skin and share the same half-life as those cells. "They may be there for several months," Dr. Weiss says. As long as a patient chronically produces IgE, the laboratory should be able to detect its presence. If the patient is not chronically exposed to the allergen or a cross-reactant type of allergen, however, a blood test may provide a lower or even negative value, while a skin test could provide a positive value if, for example, the antibody had been produced several months earlier.

"I don’t think the two tests are giving you the same information. So depending on what you’re looking for, both tests have their place," says Dr. Weiss.

Adds Dr. Reinhardt: "Total IgE levels do vary with recent exposures or symptoms, so they’re not a good source by themselves. But in vitro testing can be done at any time, even with seasonal allergies, and specific IgE levels will be readily detectable."

What else do labs need to know?

"They certainly need to know a little about botany, and the difference between plants that are pollinated by the air and plants that are pollinated by insects," Dr. Weiss suggests. "Those usually differentiate allergic-type plants and nonallergic-type plants. They also need to understand how seasons affect pollen-type allergies." Mold allergy is also tricky. When IgE antibodies to mold are measured, sometimes they work out well—and sometimes they don’t. "Pathologists should understand the nature of the mold itself as to why that might be," Dr. Weiss says.

Then there are the food allergies.

Only about 20 percent of food allergies are thought to be mediated by IgE, says Dr. Weiss, a supposition that has prompted intense discussion about other potential food allergy indicators. A negative IgE -doesn’t rule out a food allergy. "You may still have an immune reaction, but it may not be IgE," he says. "How do you find that out? What do you do to identify that? I think you need some special knowledge to help physicians select diets to try to isolate the causes of food allergies."

Even the most basic definitions—allergy versus intolerance, for example—can’t be taken for granted. The former is an immune reaction, of course, while the latter is associated with a metabolic change. But when asked if the distinction is unclear only to a lay audience, Dr. Weiss hesitates. "I don’t know," he says. "You’d be surprised at what people associate with allergies—migraines, diarrhea, bloatedness, all sorts of things that aren’t associated with a standard allergy reaction."

Pathologists who decide to pursue allergy testing should become familiar with the core of important allergens. "There’s probably about 50 of them," estimates Hitachi’s Dr. Zychlinsky. "Maybe even less. But if you’re going to do allergy testing, you need to make sure you have good quality in those allergens."

Also know that allergy testing is beset by cross-reactivities. Someone who is allergic to one mite most likely is allergic to others. "Anybody who wants to work in allergy needs to be very, very conscious of what it is they are putting into their solid phase, because that’s going to be key," says Dr. Zychlinsky.

Dr. Carpenter points to another simple yet important concept that pathologists can explain to clinicians—the difference between total IgE and allergen-specific IgE. Many clinicians mistakenly assume they only need to order the former if they’re concerned about allergy. Yet the majority of patients with allergy may have a normal IgE, or one just barely out of the normal range. "When you look at the specific IgE, though, you may find out that they have two allergens that are taking up the great majority of the IgE. Because you were only looking at the total, you would have missed the two or three things they were allergic to," she says.

It’s an important point even for pathologists who don’t do in-house allergy testing. "If you start noticing send-outs of a clinician who’s ordering just total IgEs, you can easily provide some education," says Dr. Carpenter. "Your clinicians are missing the boat if that’s all they’re looking at."

Much education can also be provided by the vendors themselves. Both Dr. Carpenter and Dr. Spatz say companies such as Pharmacia are adept at informing clinicians about using in vitro allergy testing, which has contributed to their labs’ testing volumes.

Choosing an in vitro system involves the usual amount of tire kicking and numbers crunching that accompanies any instrument selection.

At Berkshire, Dr. Spatz and his colleagues are moving their allergy testing to the Immulite 2000 analyzer, hoping the automated platform will increase the efficiency of the lab’s allergy testing. Dr. Spatz acknowledges being happy with the allergy system he’s been using; the shift is based on economics as much as anything else. "The way the deal has worked for us, by putting the allergy on the same platform as our existing immunoassays, it gives us a big enough volume to go to the bigger instrument [the Immulite 2000]," he says. "I looked at this before with DPC, and couldn’t quite come up to the point of being able to afford the bigger system. Without allergy, we wouldn’t be able to do it."

Other questions will take more time to resolve. "I still need to prove to myself, with the specimens I have, that this will be an adequate substitute in terms of the quality of results," he says.

Dr. Carpenter rounds up the usual subjects: Look at the literature, check with pathologist colleagues who do in vitro testing, study CAP Survey results, and have the leading candidates set up demos.

Finally, everyone agrees that trying to do in vitro allergy testing without the guidance of the CAP Surveys—well, it simply isn’t done.

"We watch those very carefully," says Dr. Spatz.

"You’ve got to use the CAP Surveys," agrees Dr. Carpenter.

The biggest barriers to in vitro testing may be virtual ones. It’s a matter of perception.

Allergies aren’t always taken seriously, for starters. "Most people consider allergy a nuisance disease," says Dr. Carpenter. "It’s not a life-threatening disease, although asthma can certainly be life threatening. So you think, ’If I can just treat this symptomatically, why do I need any more testing?’"

Laboratories have historically been sidestepped even when the need for allergy testing is obvious. Patients with severe allergic symptoms usually get passed along to allergists, whose bread and butter has been skin testing. At the same time, general practitioners often turn to their local specialists for information about new tests-if that specialist is an allergist, and the new method in question is in vitro testing, the deck may be stacked against it. "It’s a turf thing," says Dr. Reinhardt. Ten or 20 years ago, allergists’ sentiments against in vitro testing may have been appropriate, he says. "The older RAST tests weren’t as good and wouldn’t have been useful for primary care. But that’s all changed."

Dr. Carpenter admits she was initially worried about backlash from local allergists when her laboratory started offering in vitro testing. She didn’t need to be.

"Most of the patients who should be getting specific IgE testing, they’re never going to the allergist anyway. Only the most severe cases get referred to the allergists," she says. "We’re not cutting into that market."

Supporters of in vitro allergy testing would like to see laboratories serve as the local specialist. Dr. Homburger is quite eloquent on the subject.

"This is an issue for pathologists, especially clinical pathologists, because they serve as a resource within their hospitals to educate other physicians, especially those in primary care," he says. "Pathologists need to hear about this subject for the very reason that relatively few of them do in vitro allergy testing themselves. Nevertheless, pathologists must stay in touch with this subject if they are to serve as a resource to their clinical colleagues."

Most of those colleagues may not be aware that sound in vitro testing is available. "It’s simply not part of their clinical paradigm," says Dr. Carpenter.

Awareness could grow as new allergy treatments arrive on the market. Anti-IgE, now in phase III clinical trials, is generating considerable excitement. If it proves to be worthwhile, it won’t be cheap. "Payers will be quite demanding in terms of appropriate patient selection," predicts Dr. Reinhardt. "We would hope to see that testing by in vitro testing."

A diagnostic test to uncover circulating allergen-specific IgE antibodies would be one part of the equation, says Dr. Weiss. And anti-IgE therapy might create demand for a total IgE assay that would detect free IgE, to be used for dosing as well as monitoring therapy. Such an assay may not yet exist outside the labs involved in the drug’s clinical trials, however.

Dr. Hamilton sounds a final note of caution. Remember Dr. Hamilton? His involvement with the NCCLS document, his considerable allergy testing experience at Johns Hopkins, and his position as a consultant to the Diagnostic Immunology Resource Committee command a certain respect.

Which is why it comes as a bit of a shock when he says, "I live in an ivory tower. You have to be very careful when you listen to people like me talk."

His point is that pathologists who do allergy testing are in the minority and typically enjoy the advantages that come with working at larger academic centers or reference laboratories. "We’re not affected by the constraints of setting up these assays," he says.

While the overall volume of in vitro allergy testing has increased over the years, it’s being done in fewer laboratories—a point made clear by looking at the number of subscribers to the CAP SE-C Diagnostic Allergy Survey, he says. "Five to 10 years ago there were many, many more IgE antibody testing laboratories."

Consolidation of IgE antibody testing is being driven not only by managed care, he argues, but by the large number of allergen specificities. "It’s so expensive to get into the business, that if you don’t commit yourself totally to it, and be sort of a reference lab where people ask for these esoteric specificities, you’re going to lose money," he says. Moreover, laboratories may find themselves competing with clinicians. "The larger practices are actually setting up small IgE antibody assay labs in their offices," he says.

Yet an even bigger problem looms, Dr. Hamilton says. No matter how much they educate themselves about the subject, pathologists may find that control of allergy testing is out of their hands. "It’s in the hands of third-party payers who really don’t have their primary interest in the quality of the test, but more in the cost of the test," he contends.

"I don’t see how any of this is going to be reversed in the near future," he says.

Indeed, even the most optimistic supporters of in vitro allergy testing subscribe to the long view.

"I think the market is going to go to in vitro. But it will take education; it will take time," says Dr. Zychlinsky.

"I think that’s the way people want it to move. It will probably end up going that way over time," says Dr. Weiss. "But I don’t think it’s going that way rapidly."

Nonetheless, despite the hurdles and hindrances, the warnings and concerns, another allergy march of sorts seems to be taking place. Or perhaps "march" isn’t the best word. Perhaps it’s more of an allergy stroll toward in vitro testing, one with ample detours along the way.

Karen Titus is CAP TODAY contributing editor and co-managing editor.