3gAllergy™ Performance:
Findings of a Newly Published Comparison Study

Third-generation allergen-specific IgE (sIgE) testing on the IMMULITE^® 2000 compares favorably with the second-generation ImmunoCAP^® FEIA and with skin testing, according to a prospective study of 230 patients by Prof. Markus Ollert et al., published in the July 2005 issue of Clinical Chemistry.

Prof. Ollert's study compared IMMULITE 2000 3gAllergy and the Pharmacia ImmunoCAP (CAP) against the clinical results of skin testing. Nine allergens, comprising seven indoor and outdoor inhalant allergens and two insect venoms, were examined in this study as representative of the types of allergen typically screened in high-volume laboratories. He concluded that with 3gAllergy on an IMMULITE 2000, "laboratory testing for sIgE can be performed on a fully automated, random-access system, with an extended working range and with diagnostic accuracy for representative allergens equivalent to or better than that of the semiautomated CAP technology."

Resolution of discordant results
Of the 766 tests performed, IMMULITE 2000 and CAP results were not in agreement for 90 samples using a cutoff of 0.35 kU/L. However, skin testing results confirmed the IMMULITE 2000 assessment in 72% of these cases, compared to only 28% for the CAP (Figure 1).

"The 90 discordant results, when resolved by skin testing, showed better agreement with the IML* (72%) than with the CAP (28%)."¹

* IML = IMMULITE 2000

Insect venoms
Allergy to insect venoms can have serious clinical consequences, including anaphylaxis. Anaphylaxis is characterized by

· Generalized urticaria
· Angioedema
· Loss of blood pressure
· Loss of pulmonary function
· Anaphylactic shock/cardiac arrest.

According to the National Institute of Allergy and Infectious Diseases (NIAID), between 40 and 100 people die each year from anaphylactic reactions to insect stings from yellow jackets, hornets, wasps, bees and fire ants.

Diagnostic parameters for investigating venom allergies include a patient history and physical exam, skin tests and in vitro tests for allergen-specific IgE. Clearly, skin tests must be used with caution and in vitro tests must be highly sensitive, as insect venom allergies can elicit a severe anaphylactic response even if the patient has only a low level of sIgE. Highly successful therapy for venom allergies is available with specific immunotherapy.

Two venom allergens, yellow jacket and honey bee, were included in the study. When compared to skin testing, IMMULITE 2000 had significantly better agreement than CAP (Table 1, Figure 1).

"For both venom allergens, we found a significant difference in favor of the IML."¹

Table 1. Agreement between in vitro sIgE results and in vivo skin test results. (Based on Ollert et al., Table 2 and Figure 3a.)

click image to enlarge

Figure 1. Resolution of in vitro sIgE results discordant by IML and CAP: percentage of skin testing results that confirmed the sIgE result of one assay method or the other. The absence of a bar at G3 for CAP signifies no agreement of skin test results. (Based on Ollert et al., Figure 3b.)

"A substantial fraction of the sIgE concentrations, as measured by the IML, fall in the 0.10–0.35 kIU/L interval."¹

Aeroallergens
Prof. Ollert found that for the seven inhalant allergens tested, 3gAllergy showed statistically significantly better agreement with skin testing than did CAP (Table 1, Figure 1).

Furthermore, a substantial number of results that could not be accurately measured on the CAP because of its 0.35 kU/L detection limit were measurable on the IMMULITE 2000. The measuring range for 3gAllergy is 0.10 to 100 kU/L. In contrast, the CAP system can measure no lower than 0.35 kU/L, with estimated values below 0.35 kU/L achieved, if at all, only by extrapolation. Cumulative distribution analysis (CDA) plots presented in the article and its online supplements illustrate IMMULITE's broader measuring range, which allowed more of the skin-test positive samples to be recorded as positive by the IMMULITE 2000 than by CAP: 92% vs. 82%, respectively.

"Both the highest clinical sensitivity achievable and . . . the highest sensitivity and specificity jointly attainable were always higher for IML than for CAP."¹

Third-generation sensitivity and specificity
ROC analyses showed a greater area under the curve (AUC) for IMMULITE 2000 than for CAP for all nine allergens studied. The increased AUC demonstrates that 3gAllergy has greater diagnostic accuracy than CAP.

Setting a new standard in allergy testing
3gAllergy is the first FDA-cleared third-generation assay for allergen-specific IgE. It is available on the fully automated IMMULITE 2000 and IMMULITE^® 2500 systems to help physicians identify, monitor and manage patients with allergies. With an expanding menu of over 375 specific allergens and allergen panels, the IMMULITE^® systems consolidate in vitro allergen-specific IgE testing with over 75 other immunoassays on a true random-access platform that yields allergy results in about one hour.

Consolidating in vitro allergy testing with other routine and esoteric immunoassays on one platform is an efficient use of laboratory personnel and physical space resources. Because 3gAllergy is performed just like any other immunoassay, it eliminates the need for dedicated equipment or extensive training of staff. Currently in routine use in over 45 countries worldwide, 3gAllergy sets a new standard for in vitro sIgE testing.

3gAllergy has advanced in vitro allergy testing to a new level of precision, with excellent accuracy and lot-to-lot reproducibility. The assay is validated according to NCCLS guidelines and standardized against the WHO 2nd International Reference Preparation (IRP) 75/502. A zero calibrator combined with enzyme-enhanced chemiluminescence and liquid-allergen technology allows for a low-end detection limit of 0.10 kU/L and a functional sensitivity of 0.20 kU/L. This makes 3gAllergy the first assay capable of precisely measuring allergen-specific IgE at these very low concentrations without extrapolation, while maintaining calibration in terms of the WHO IRP.

DPC's proprietary liquid allergens are the key to making sIgE testing on the IMMULITE 2000 and IMMULITE 2500 sensitive, specific and reliable. The soluble polymer-copolymer support for the allergens increases the number of binding sites and their accessibility to allergen-specific IgE antibodies. The proprietary wash technique of the IMMULITE 2000 and IMMULITE 2500 enhances specificity.

Conclusion
Prof. Ollert's study concludes that in vitro testing for sIgE with 3gAllergy on the fully automated, random-access IMMULITE 2000 compares favorably with skin testing and is equivalent to or better than the second-generation CAP technology.

Reference
1. Ollert M, Weissenbacher S, Rakoski J, Ring J. Allergen-specific IgE measured by a continuous random-access immunoanalyzer: interassay comparison and agreement with skin testing. Clin Chem 2005;51:1241-9.