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Allergy testing is performed
to establish whether atopy is the basis for allergy-like
symptoms
and to identify potential specific etiology, which should
lead to appropriate therapeutic recommendations. Two types
of diagnostic tests are available for measuring allergen-specific
IgE—
in
vitro IgE
blood testing and in vivo skin
testing.
An important diagnostic tool
A careful patient history, in addition to a physical examination,
provides important clues to the physician. In vitro
tests that measure the presence of IgE antibodies can be
used to identify atopic individuals, determine the specific
allergens to which they are sensitive, and assess their
risk for evolution of more serious diseases.1 In
vivo tests
can also be used, although they are dependent on the experience
of the tester and the quality of the extracts used.1 In
addition, this form of testing requires that the patient
discontinue antihistamines and other medications at least
3 days before using,1,2 and
may be hazardous to the highly sensitized patient.1
Blood testing technology
Allergen-specific in vitro blood testing is an easy
procedure that is at least equivalent to skin testing in
efficacy.1,2 It
can be performed in the physician's office lab (CLIA moderate
license) or sent to one of hundreds of reference
labs. With this kind of testing, the patient need not
discontinue medications.
Not all in vitro tests are alike, however. The
most accurate and commonly used technology, ImmunoCAP
Specific IgE blood test, is vastly superior to RAST™
technology, which was first introduced by Pharmacia in 1974.
ImmunoCAP has been cleared by the FDA as a truly quantitative
measure of IgE.
ImmunoCAP Specific IgE blood test provides:
- More true positives than RAST
- Higher sensitivity than RAST
- True negatives (no significant atopy)
- Consistently acceptable coefficient of determination
(R2) values 3
Accuracy of Immunoassays for
Specific IgE
In clinical tests, ImmunoCAP technology has
been demonstrated to be close to an ideal lab determination.
In a key comparison study,3
illustrated above, laboratories evaluated more than 12,000
blinded serum samples containing various levels of specific
IgE, using a number of lab tests in order to compare accuracy
and precision.
ImmunoCAP technology produced the best assessments at 96-98%
of the ideal standard. RAST tests ranged from 65-82%. As
the researchers concluded, ImmunoCAP performed well when
compared with the standard of an ideal assay, although other
assays often did not perform up to this standard.
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