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