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Original Article
Phadiatop Assay와 AdvanSureTM AlloScreen의 임상적 유용성 비교
Comparison of Clinical Utility between Phadiatop Assay and AdvanSureTM AlloScreen
성균관대학교 의과대학 강북삼성병원 진단검사의학과
Department of Laboratory Medicine, Sungkyunkwan University School of Medicine, Kangbuk Samsung Hospital, Seoul, Korea
Correspondence to:This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Lab Med Online 2020; 10(4): 301-306
Published October 1, 2020 https://doi.org/10.47429/lmo.2020.10.4.301
Copyright © The Korean Society for Laboratory Medicine.
Abstract
방법: AlloScreen 검사 결과에 따라 분류된 총 218개의 검체를 수집하였다. 흡입알레르겐에 대해 양성을 보이는 61개 검체와 103개의 음성 검체에 대해 Phadiatop test를 시행하였다. 음식 및 흡입알레르겐에 대해 양성을 보이는 54개 검체와 103개의 음성 검체 대하여 Phadiatop Infant test 검사를 시행하였다. Phadiatop과 AlloScreen의 결과가 일치하지 않은 경우, ImmunoCAP (Phadia AB, Sweden)을 사용하여 확인하였다.
결과: AlloScreen과 Phadiatop test 간의 일치율은 93.2% (κ=0.86, P<0.001)이었다. 164개 검체 중 11개(6.7%)가 불일치 결과를 보였다. AlloScreen의 결과가 ImmunoCAP 결과와 일치하지 않았다. AlloScreen과 Phadiatop Infant test 간의 일치율은 97.4% (κ=0.945, P<0.001)이었다. 4개(2.5%)의 검체는 AlloScreen 음성, Phadiatop Infant test 양성이었다. ImmunoCAP 검사에서 3개 검체는 양성으로 확인되었고 1개 검체는 확인되지 않았다.
결론: AlloScreen과 Phadiatop assay는 높은 일치율을 보였으며Phadiatop assay는 빈도가 높은 식품 및 흡입 알레르겐 혼합물에 대한 감작을 정확하게 검출하였다. 따라서 Phadiatop assay는 알레르기 질환에 대한 선별 검사로 권장된다.
Methods: A total of 218 samples classified by AlloScreen results were collected. Phadiatop test was performed on sera from 61 and 103 aeroallergen-positive and -negative subjects. Phadiatop Infant test was performed on sera from 54 and 103 food and aeroallergen-positive and -negative subjects. When the results of AlloScreen and Phadiatop assay were not identical, we confirmed them using ImmunoCAP (Phadia AB).
Results: The concordance rate between AlloScreen and Phadiatop test was 93.2% (κ=0.86, P<0.001). Eleven (6.7%) of 164 specimens showed discrepant results. The results of AlloScreen did not agree with those of ImmunoCAP. The concordance rate between AlloScreen and Phadiatop Infant test was 97.4% (κ=0.945, P <0.001). Four (2.5%) specimens showed negative results in AlloScreen and positive results in Phadiatop Infant test. Three cases were confirmed as positive and one case was not confirmed through ImmunoCAP.
Conclusions: There was excellent agreement between AlloScreen and Phadiatop assay. Phadiatop assay accurately detected sensitization to common food and aeroallergen mixes. Therefore, Phadiatop assay is recommended as a screening test for allergic diseases.
Keywords
INTRODUCTION
Allergic diseases are commonly referred to as “allergy”, and the word was first used by Clemens von Pirquet in 1906 [1]. Allergic diseases are caused by hypersensitivity of the immune system to typically harmless substances in the environment. The underlying mechanism involves the binding of immunoglobulin E antibody (IgE) to an allergen and then to mast cells or basophil receptors, where it triggers the release of inflammatory cytokines, such as histamine [2]. Allergy has various manifestations, ranging from mild symptoms, such as red eye and pruritus, to anaphylaxis, which can lead to death [3]. It is important to identify the culprit allergen a patient is sensitized to, as sensitization varies between patients and allergen avoidance is the best treatment.
Allergy screenings and diagnoses are commonly conducted using the skin-prick test (SPT) and allergen-specific IgE (sIgE) tests [4, 5]. SPT is the most common method for confirming the IgE-mediated underlying mechanism of allergic diseases, as it is easy to perform, sensitive, cost-effective, and provides prompt results [6]. However, SPT has several limitations, such as its qualitative-only nature, unstandardized amount and choice of allergen, interference from antihistaminergic drugs, and subjective interpretation. Measurement of serum sIgE is a convenient method for patients who cannot discontinue the use of a drug that could interfere with SPT [7]. Among
In this study, we compared the clinical utility of Phadiatop assay (Phadiatop test and Phadiatop Infant test) with that of AlloScreen.
MATERIALS AND METHODS
1. Specimens
This study was performed between December 2018 and June 2019. Serum samples were collected from 218 subjects who were requested for MAST allergy screening. Characteristics of the subjects are described in Table 1. We collected 61 samples that were positive for aeroallergens [
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Table 1 . Characteristics of subjects (N=218)
Characteristics Values Age (yr) 40.75 (0.7-82) Sex (male:female) 98:120 Total IgE (IU/L) 129.57±91.57 Diagnosis Allergic rhinitis 9 (4.1) Asthma 7 (3.2) Atopic dermatitis 26 (12) Chronic urticaria 28 (12.9) Other skin diseases 95 (43.5) Other respiratory diseases 22 (10.1) Others 31 (14.2) Values are presented as mean (range), number (%), or mean±standard deviation.
This study was approved by the Institutional Review Board of Kangbuk Samsung Hospital (2018-05-060) and conducted in compliance with the World Medical Association Declaration of Helsinki.
2. Allergy screening tests
We used two types of allergy screening tests, and comparison of characteristics between AlloScreen and Phadiatop assays is presented in Table 2.
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Table 2 . Comparison of characteristics between AlloScreen and Phadiatop assay
Characteristics AlloScreen Phadiatop assay Principle Immunoblot Solid-phase fluorescence immunoassay Degree of automation Semi automation Full automation Number of antigens 62 Not published Minimal sample volume (μL) 100 40 Number of tests per run 24 up to 350 Analysis time per run (hr) 3.5 1.7 Analysis time per sample (min) 8.75 1.0
1) AlloScreen assay
AlloScreen assay is a multiplex test that simultaneously detects total IgE and sIgE responses against multiple allergens. Total IgE is classified into positive and negative with a cutoff of 100 IU/mL. Test strips were read using AdvanSure AlloScreen (LG Life Science, Korea). The software determined the class (0–6) of sIgE concentrations. In this study, samples were considered positive for an allergen if the sIgE concentration was greater than class 1 (sIgE ≥0.35 kU/L) [12].
2) Phadiatop assayPhadiatop assay, a solid-phase fluorescence immunoassay for serum sIgEs using a mixture of relevant allergens, was analyzed quantitatively in a Phadia 250 System (Phadia AB). This assay provides simultaneous graded determinations of sIgEs for multiple allergens. The manufacturer does not reveal the precise composition of allergens included in Phadiatop assay. According to the published reports, Phadiatop Infant test might include egg white, cow’s milk, peanut, wheat, soybean, shrimp, cat epithelium and dander, dog dander, house dust mites, common silver birch, mugwort, and ragweed allergens, whereas Phadiatop test might include
3. ImmunoCAP Allergen-sIgE test
In the case of discrepancies between AlloScreen and Phadiatop assay, we confirmed the results using ImmunoCAP test, which measures sIgE for an individual allergen. Serum samples were analyzed for individual allergen-sIgEs with a Phadia 250 Immunoassay Analyzer (Phadia AB, Sweden). Levels ≥0.35 kUA/L were considered positive.
ImmunoCAP sIgE tests for 16 popular allergens were performed on specimens with negative AlloScreen results and positive Phadiatop assay results. The 16 popular allergens included 9 aeroallergens (
4. Data analyses
We compared the concordance rate and degree of agreement of AlloScreen and Phadiatop assay. Phadiatop test and Phadiatop Infant test were both evaluated for percent positive agreement (PPA) and percent negative agreement (PNA). When the results of AlloScreen test were concordant with those of Phadiatop assay, the results were considered reference results. When the results of AlloScreen and Phadiatop assay were discrepant, the results of ImmunoCAP assay were considered reference results. We used kappa statistics and McNemar test to compare the degree of agreement between the two screening allergy tests. Kappa values of 0.8-1.0 are considered almost perfect [14]. All statistical analyses were performed using the SPSS software, version 24.0 (SPSS Inc, Chicago, IL, USA).
RESULT
A total of 164 samples (61 and 103 samples positive and negative for aeroallergens, respectively) were tested using Phadiatop test and 157 samples (54 and 103 samples positive and negative for food allergens, respectively) were tested with Phadiatop Infant test.
The concordance rate between AlloScreen and Phadiatop test was 93.2% (κ=0.86,
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Table 3 . ImmunoCAP results of discrepant cases (N=14) between AlloScreen and Phadiatop assay (Phadiatop test and Phadiatop Infant test)
No. MAST results ImmunoCAP results, kUA/L (class) AlloScreen (IU/mL) Phadiatop assay (PAU/L) d1 d2 w1 w6 f1 f2 f24 N12 Negative (72.46) Positive (0.38) 0.10 (0) 0.01 (0) 0.21 (0) 0.48 (1) ND ND ND N32 Negative (30.18) Positive (0.40) 0.02 (0) 0.01 (0) 0.00 (0) 0.51 (1) ND ND ND N44 Negative (96.18) Positive (0.68) 0.18 (0) 0.99 (2) 0.00 (0) 0.00 (0) ND ND ND N58 Negative (92.21) Positive (0.43) 0.21 (0) 0.44 (1) 0.00 (0) 0.12 (0) ND ND ND N68 Negative (84.58) Positive (1.87) 0.46 (1) 2.54 (2) 0.04 (0) 0.04 (0) ND ND ND N79 Negative (12.93) Positive (0.88) 0.20 (0) 0.98 (2) 0.00 (0) 0.00 (0) ND ND ND N86 Negative (23.70) Positive (0.35) 0.64 (1) 0.81 (2) 0.01 (0) 0.18 (0) ND ND ND N100 Negative (77.86) Positive (0.37) 0.52 (1) 0.39 (1) 0.00 (0) 0.00 (0) ND ND ND N21 Negative (63.53) Positive (0.38)* ND ND ND ND 0.14 (0) 0.27 (0) 0.03 (0) N60 Negative (56.55) Positive (0.39)* 0.01 (0) 0.02 (0) ND ND 0.17 (0) 0.41 (1) 0.04 (0) N83 Negative (80.27) Positive (0.42)* ND ND ND ND 0.00 (0) 0.03 (0) 1.89 (2) N87 Negative (3.31) Positive (0.42)† 1.10 (2) 2.84 (2) 0.00 (0) 0.00 (0) 0.00 (0) 0.01 (0) 0.01 (0) I18 Positive (248.30)§ Negative (0.31) 0.31 (0)† 0.30 (0) ND ND ND ND 0.10(0) I19 Positive (110.80)∥ Negative (0.30) 0.02 (0)† 0.34 (0) ND ND ND ND 0.03(0) Discrepant cases showed values <0.16 kUA/L by ImmunoCAP assay for the following allergens and data are not described: e1, cat; e5, dog; m6,
Alternaria alternata ; i6, cockroach; t7, oak; f3, fish (cod); f4, wheat; wheat; f14, soybean; f13, peanut. Phadiatop assay values ≥0.35 PAU/L, AlloScreen values >100 IU/mL, and ImmunoCAP values ≥0.35 kUA/L are considered positive. N21 was not confirmed.*These are the results of Phadiatop Infant test. †This is a result of both Phadiatop test and Phadiatop Infant test. †Test for hx2 (house dust mixes) also showed negative results. §Positive result for
D. pteronyssinus (I18). ∥Positive result forD. farinae (I19). d1,D. pteronyssinus ; d2,D. farinae ; w1, ragweed; w6, mugwort; f1, egg white; f2, cow’s milk; f24, shrimp, ND; not done.
The concordance rate between AlloScreen and Phadiatop Infant test was 97.4% (κ=0.945,
As the results of Phadiatop test were completely concordant with the gold standard, both the sensitivity and specificity of Phadiatop test were 100%. The sensitivity and specificity of Phadiatop Infant test were 100% and 99%, respectively.
DISCUSSION
We assessed the clinical utility of Phadiatop test and Phadiatop Infant test in comparison with that of AlloScreen, based on ImmunoCAP assay. No study has compared AlloScreen with Phadiatop or Phadiatop Infant tests. Only one study had compared Phadiatop test to RIDA qLine allergy test (R-Biopharm AG, Darmstadt, Germany), which is a MAST, with ImmunoCAP sIgE test as a reference method [7]. A total of 430 consecutive specimens from patients with allergic symptoms were tested. The concordance rate between the two tests was 80.7% (κ=0.614,
In our study, almost perfect concordance was observed between AlloScreen and Phadiatop test and between AlloScreen and Phadiatop Infant test. There were 11 (6.7%) discrepant results between AlloScreen and Phadiatop test, and 4 (2.5%) discrepant results between AlloScreen and Phadiatop Infant tests. Phadiatop assays, including Phadiatop test and Phadiatop Infant test, were revealed to be more accurate than AlloScreen, as confirmed by ImmunoCAP assay. However, the possibility of false negative results caused by low sIgE levels or false positive results due to nonspecific antibody binding cannot be completely excluded, and thus clinical correlation and confirmation tests such as SPT are necessary. Two results (I18 and I19) that were read as positive by AlloScreen and negative by Phadiatop for
In this study, Phadiatop assay provided accurate information about the possibility of allergic diseases. Phadiatop assay can also be helpful in health screening because it has a similar accuracy to ImmunoCAP assay, the gold standard method. However, Phadiatop assay has less allergens than AlloScreen. Moreover, it cannot identify particular sIgEs, and only detects the presence of sIgE for unspecified allergens. Therefore, further examination and a specialist’s opinion are required for accurate diagnosis and treatment. Phadiatop test may need more than one sampling for confirmation, as it does not detect which allergen was positive. In contrast, AlloScreen provided an sIgE result for each allergen, and thus would be more suitable for young children, in whom blood sampling is difficult.
There are some limitations in our study. First, the number of specimens was relatively small, and thus further studies are needed for more accurate evaluation. Second, false positivity and false negativity of AlloScreen assay were confirmed based on ImmunoCAP test results, not on clinical manifestation or SPT results. Third, as the panel of allergens for Phadiatop assay is not publically available, we performed ImmunoCAP assay only on common allergens. Finally, the cutoff value for sIgE positivity can differ between allergens [15], but values of ≥0.35 PAU/L were considered indicative of sensitization and were coded as positive in our study.
In summary, compared with AlloScreen, Phadiatop assay can be used to test for fewer allergens and did not provide positive results for specific allergens, but more accurately detected the presence of sIgE for common allergens, such as D. pteronyssinus, D. farinae, mugwort, and birch. Therefore, Phadiatop assay may be useful as a one-shot screening test for subjects with suspected allergic diseases.
Conflicts of Interest
None declared.
Acknowledgments
We thank Thermo Fisher Scientific for technical support and for donating the reagents used in this study.
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