Comparison of probability curves obtained from 2 quantitative allergen-specific IgE assays: FEIA and 3gAllergy[TM].
Immunoglobulin E (Research)
|Publication:||Name: American Journal of Immunology Publisher: Science Publications Audience: Professional Format: Magazine/Journal Subject: Biological sciences Copyright: COPYRIGHT 2005 Science Publications ISSN: 1553-619X|
|Issue:||Date: April, 2005 Source Volume: 1 Source Issue: 2|
|Topic:||Event Code: 330 Product information; 310 Science & research|
|Product:||Product Code: 2831650 Enzymes for Immunoassay NAICS Code: 325413 In-Vitro Diagnostic Substance Manufacturing SIC Code: 2835 Diagnostic substances|
|Geographic:||Geographic Scope: United States Geographic Code: 1USA United States|
Abstract: The validity and benefit of probability curves in
allergen-specific IgE (sIgE) testing and their applicability to more
than a few allergens are still pending. One study  presented
probability curves for 4 food allergens and proposed decision points to
rule out the need for food challenges in his clinic. Since then, such
cutoffs were reported by Boyano-Martinez  to be dependent on
population, age, allergen and disease. A recent article by Soderstrom
 extended the use of probability curves to 8 inhalant allergens. The
results were allergen dependent and site specific. None of the studies,
however, has addressed the potential impact of IgE specific for
cross-reacting carbohydrate determinants (CCD) on these probability
curves . In this study, we use logistic regression model to compare
the probability curves for food and inhalant allergens using two
quantitative sIgE assays; an FEIA (Pharmacia CAP) and DPC's
automated chemiluminescent IMMULITE[R] 2000. The FEIA yields explicit
results down to 0.35 kU [L.sup.1]; the "third-generation"
IMMULITE 2000 has an analytical sensitivity of 0.1 kU [L.sup.1] and
provides precise quantification down to 0.2 kU [L.sup.1]. In previous
studies [6,7], patients with suspected IgE-mediated allergy were
evaluated according to skin prick tests or food challenges positive or
negative allergen-specific diagnosis. Logistic regression was performed
using the online regression analysis facility at:
http://members.aol.com/johnp71/logistic.html, which is part of the
Interactive Statistical Calculations web site. For inhalant allergens,
almost identical overall probability curves were obtained for the FEIA
and IMMULITE 2000 methods. For food allergen, similar probability curves
were obtained with the two methods. The probability curves were allergen
dependent. The FEIA and IMMULITE 2000 methods gave similar
allergen-dependent profiles, however and in one case (W6), both methods
yielded identical probability curves. The present study demonstrates
that the 2 sIgE assays yield comparable probability curves for the
inhalant and food allergens tested. Because the FEIA method is unable to
yield explicit results below 0.35 kU [L.sup.1], the probability curve
generated is necessarily truncated at this level. Methods for sIgE
measurement that allow for extending probability curves below 0.35 kU
[L.sup.1] can also assess assay performance more definitively at the
traditional 0.35 kU [L.sup.1] cutoff. Thus the third-generation IMMULITE
2000 is a better tool for defining probability curves, as the
applicability of such curves in allergy testing and the potential impact
of IgE to CCD become well understood.
Key words: Fluorescent enzyme immunoassay, IMMULITE[R] 2000 THIRD Generation Allergen-specific IgE, logistic regression, odds ratios, probability curves
Sampson  presented probability curves for four food allergens and proposed decision points, which could be used to eliminate the need for double-blind, placebo-controlled food challenges in his clinic. In his report, the curves illustrate graphically that even a low concentration of food-specific IgE antibodies might be associated with a risk of clinical reactivity. Since then, other investigators  have concluded that cutoff levels, however, depended on population, age, allergens and diseases. Soderstrom et al.  extended the concept of probability curves to inhalant allergens. His study on eight allergens evaluated at four separate clinics deals with the question whether high risk was associated with higher levels of sIgE and whether quantitative results were more useful than qualitative (positive/negative) determinations. He speculated that the concept of probability for an allergic reaction or positive clinical allergy conclusion would be a better diagnostic tool compared with the traditional qualitative measures including class correlation. None of the studies, however, has addressed the potential impact of IgE specific for cross-reacting carbohydrate determinants (CCD) on these probability curves .
The Soderstrom study  has led to many unanswered questions . The implications of obtaining different probability curves among different clinics for the same allergens are not clear. Factors affecting the shapes of the curves are also not entirely known or explained. For instance, why are the curves for D1 and E1 so different at the four clinics?
In previous studies [6,7], patients with suspected IgE-mediated allergy were evaluated according to skin prick tests and food challenges, respectively. The objective of our study was to apply the logistic regression model in order to compare the probability curves for one food (F2), two insects (I1 and I3) and seven inhalant (D1, D2, E1, G3, G6, T3 and W6) allergens, obtained from two quantitative sIgE methodologies: FEIA and IMMULITE 2000 Third Generation, (3gAllergy).
MATERIALS AND METHODS
Logistic regression was performed using the online regression analysis facility at: http://members.aol.com/johnp71/logistic.html, which is part of the Interactive Statistical Calculations web site.
For the two insects and seven inhalant allergens, we used skin prick tests  in clinic 1 as the true status. For F2, we used food challenges in clinic 2  as the true status. The same blood samples were subject to FEIA and 3gAllergy analysis.
In the study performed at clinic 1, almost identical overall probability curves (Fig. 1) were obtained for the FEIA and 3gAllergy methodologies, using the two insects and seven inhalant allergens with N=766 results. Overall model fit gave Chi Square of 308.4 and 253.0, respectively with df=1 and p= 0.0001.
[FIGURE 1 OMITTED]
For the F2 food allergen study done in clinic 2, similar F2 probability curves (Fig. 2) were obtained for the FEIA and 3gAllergy methodologies: N=31 results. Overall model fit gave Chi Square of 19.1 and 17.1, respectively with df=1 and p= 0.0001.
[FIGURE 2 OMITTED]
In agreement with Soderstrom's report, probability curves are allergen dependent. The two FEIA and 3gAllergy methodologies, however gave similar allergen dependent profiles (Fig. 3 and 4). With certain allergens, the 2 methodologies can yield identical (W6) probability curves (Fig. 5).
[FIGURES 3-5 OMITTED]
According to Gallagher, a positive ratio of 1 to 2 alters disease probability by a small and clinically insignificant degree. Positive ratios greater than 10 may have substantial impact on clinical decision making through meaningful revision of disease probability. Table 1 indicates there are no significant differences in the odds ratios among all of the 10 allergens evaluated.
This study demonstrates that probability curves for the two insects, seven inhalant allergens and one food allergen generated via two quantitative sIgE assays are comparable. The FEIA and 3gAllergy probability curves give odds ratios that differ by no clinical significance.
Because the FEIA methodology uses 0.35 kU [L.sup.1] as cut off, the probability curve generated begins at 0.35 kU [L.sup.1] (Fig. 6). Soderstrom commented that different slopes and intercepts in probability curves may indicate different identification patterns of symptoms; a steep curve would indicate symptoms easily linked to an allergen even with low levels of IgE antibodies. A more flat curve in contrast, would indicate a difficulty to link even high levels of IgE antibodies as the trigger of the symptoms. Probability curves extending below 0.35 can provide a more complete curve profile (the I3 probability curves in Fig. 7) and can be useful for the assessment of the true slope and intercept. Thus the 3gAllergy methodology which provides precise quantification down to 0.2 kU [L.sup.1] [9,10] can offer a better tool in defining the probability curve profile.
[FIGURES 6-7 OMITTED]
[1.] Sampson, H.A., 2001. Utility of food-specific IgE concentrations in predicting symptomatic food allergy. J. Allergy Clin. Immunol., 07: 891-6.
[2.] Boyano, M.T., C. Garcia-Ara, J.M. Diaz-Pena, F.M. Munoz, G. Garcia Sanchez and M.M. Esteban, 2001. Validity of specific IgE antibodies in children with egg allergy. Clin. Exp. Allergy, 31: 1464-9.
[3.] Soderstrom, L., A. Kober, S. Ahlstedt, H. de Groot, C.E. Lange, R. Paganelli et al., 2003. A further evaluation of the clinical use of specific IgE antibody testing in allergic diseases. Allergy, 58: 921-8.
[4.] Mari, A., 2002. IgE to cross-reactive carbohydrate determinants: analysis of the distribution and appraisal of the in vivo and in vitro reactivity. Intl. Arch. Allergy Immunol., 129: 286-95.
[5.] Malandain, H., 2004. The clinical use of specific IgE antibody testing--a further word of caution [letter]. Allergy, 59: 359-60; author reply 360-1.
[6.] Markus, O., S. Weissenbacher, J. Rakoski and J. Ring, 2005. Allergen-specific IgE measured by a continuous random-access immunoanalyzer: interassay comparison and agreement with skin testing.
Clin. Chem., 51: 1241-1249.
[7.] Prates, S., 2003. IMMULITE 2000 and cow's milk allergy: a clinical perspective. In: Diagnostic Products Corporation (DPC). Proc. DPC's Intl. Allergy Conf., Jun. 6, Paris, France.
[8.] Gallagher, E.J., 1998. Clinical utility of likelihood ratios. Ann. Emerg. Med., 31: 391-7.
[9.] Li, T.M., T. Chuang, S. Tse, D. Hovanec-Burns, A.S. El Shami, 2004. Development and validation of a third generation allergen-specific IgE assay on the continuous random access IMMULITE 2000 analyzer. Ann. Clin. Lab. Sci., 34: 67-74.
[10.] Li, T.M. et al., 2005. Performance validation of a third generation allergen-specific IgE assay in the clinical laboratory: Interlaboratory and intermethod comparison. Clin. Chim. Acta, 361: 199-205.
T.M. Li, T Chuang, S.M. Li and D. Hovanec-Burns
Invitrogen, Carlsbad, CA and Diagnostic Products Corporation, Allergy and Immunology Los Angeles, CA
Corresponding Author: T M Li, Invitrogen, Carlsbad, CA and Diagnostic Products Corporation, Allergy and Immunology, Los Angeles, CA
Table 1: Comparison of odds ratios between the 2 methodologies Odds Ratios FEIA Immulite 2000 Difference D1 1.0575 1.0738 0.0163 W6 2.2821 2.2489 0.0332 ALL 1.2964 1.1829 0.1135 E1 1.1856 1.0566 0.129 D2 1.8879 1.6615 0.2264 F2 1.4072 1.1047 0.3025 G6 1.7076 1.2677 0.4399 G3 1.7202 1.2015 0.5187 I3 2.6032 2.0257 0.5775 I1 1.1359 3.4914 2.3555 T3 2.0204 4.582 2.5616
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