To the Editor,
Precision medicine is increasingly used as an approach to the management
of allergy and anaphylaxis, thanks to progress in diagnostic tests and
biomarkers now allowing thorough characterization of a patient’s
endotype1. Probability-based risk assessment and
diagnostic algorithms have entered the allergists’
toolbox2-4. Allergy tests must therefore offer
reliable, robust, and proficient results in each patient. Focusing onin vitro diagnostics, these requirements have led to the
development of quality assurance (QA) programs for allergy laboratory
assays and their implementation in virtually all clinical laboratories
performing allergy assays. However, full performance targets for allergy
assays have not yet been established, leaving allergists and clinical
scientists without a common body of recommendations for the three
routine assays, namely total serum IgE (tIgE), allergen-specific serum
IgE (sIgE), and serum total tryptase. As an example, not only do
recommendations on the acceptable bias and uncertainty of measurement
(UM) of allergy assays miss from available literature, but there is also
a complete lack of published recommendations on tryptase QA criteria.
The multicentric French network of public clinical laboratories had
previously documented a single-analyte QA strategy and recommendation
for sIgE5. Hence, we set out to define QA criteria for
intra- and interassay variation, analytical accuracy, and UM for sIgE,
tryptase, and tIgE. QA data from 24 French centers were collected,
analyzed, and compared to available literature, prior to issuing
recommendations for QA management programs in allergy testing.
Data were collected from 2016-2018 intralaboratory (internal) QA
controls (IQA) and interlaboratory proficiency testing programs
(external quality assurance, EQA) completed by the participant
centers6. A literature search for English and French
recommendations for allergy assays was performed, including scientific
publications, statements of scientific societies, QA management schemes
from independent QA organisms, and manufacturer documents. According to
the regulated (tIgE) or nonregulated (sIgE, tryptase) analyte
status7, the current work applies to any tIgE system,
but for sIgE and total tryptase it is limited to the ImmunoCAP assay
system, which is in use in all participant centers, is currently
perceived as the reference in vitro diagnostic method for
allergy2, and offers the only EU-cleared tryptase
determination method. Briefly, IQA programs were performed with control
samples provided by the manufacturer and with internal serum pools,
particularly for tryptase determination. EQA programs were from UK NEQAS
(UK National External Quality Assessment Services), Thermo Fisher
Scientific (Uppsala, Sweden), ProBioQual (Lyon, France), and CTCB
(Toulouse, France). All participant laboratories had subscribed to at
least one EQA for each assay. Data analysis was performed stepwise: (1)
definition of three concentration levels (low, medium, and high) within
the dynamic range of each analyte and assignment of measurement results
from each center to the corresponding level; (2) computation and
analysis of intra- and interassay coefficient of variability (CV), bias
from analytical accuracy, and UM for each analyte, concentration level,
and participant; (3) comparison of assay performance of participant
centers with extant recommendations, outlier identification and
establishment of recommendations. Performance evaluation criteria were
defined as follows: CV = 100xSD/mean (SD, standard deviation), bias =
100x[(participant result) – (peer group target result)]/(peer group
target result), UM = √ [u2(IQA) +
u2 (IQA)], with u2(IQA) denoting the variance
(square SD) of all IQA results of the same concentration level, and
u2(EQA) denoting the variance of corresponding EQA
results8.
Comparison of participant centers’ results and available recommendations
(Table 1 ) revealed that actual tIgE assays outperformed most
intra- and interassay CV recommendations, but were in line with bias
recommendations. Actual sIgE assay performance for intra-and interassay
CV matched the available non-manufacturer recommendations from CLSI
(Clinical and Laboratory Standards Institute)9, but
inconsistently attained UK NEQAS standards (Table 1 ). Intra-and
interassay CV for total tryptase determination could only be compared to
manufacturer recommendations, which appeared too stringent for
inter-assay CV. Similarly, actual accuracy bias for tryptase
determination was less performant than the available UK NEQAS standards,
designed for low concentration levels (Table 1 ). For the three
analytes and each concentration level, UM was calculated but due to a
complete lack of available recommendations it could not be evaluated
outside the peer group. Moreover, due to the lack of adequate EQA for
each tryptase level, the UM for low (< 8 µg/L) and medium
(8-20 µg/L) could only be computed for a combined low and medium
concentration level up to 20 µg/L (Table 1 ).
Analysis of data from participant centers and comparison with
international standards (when available) allowed the establishment of
recommended targets for performance evaluation, defined as the
95th percentile of the participants’ results
(Table 2 ). It is noteworthy that UM, a performance criterion
that should be considered whenever clinical interpretation and decision
rely on quantitative results, needs improvement, both in terms of
availability of adequate EQA samples spanning the whole range of analyte
concentrations, and of results from participating centers. The first
step to take is wider availability of IQA and EQA samples of paired
concentration levels. As UM computation is based on the absolute value
of variance, UM of low concentrations of an analyte is unfavorably
impacted by the use of medium or high EQA sample results. In order to
achieve the goal of using adequate pairs of EQA samples for each analyte
level, in the absence of commercially available EQA programs,
interlaboratory exchanges are a simple, cost-effective solution.
In conclusion, we report here the first experience-based performance
results for the most usual in vitro allergy and anaphylaxis
assays, their comparison with available recommendations, and the
establishment of the first recommendations for total tryptase assays and
for the uncertainty of measurement of the three considered analytes:
total serum IgE, allergen-specific serum IgE, and total serum tryptase.
Conceived as a working tool for allergists and clinical scientists, our
report aims at incentivizing further improvement and better use ofin vitro allergy assays for precision medicine.
Anne Sarrat1, Rémy Couderc2,
Marie-Alexandra Alyanakian3, Pol-André
Apoil4, Céline Beauvillain5, Lionel
Chollet6, Pascale Chrétien7, Arnaud
Cirée8, Benoît Cypriani9, Erwan
Dumontet10, Bertrand Evrard11, Lorna
Garnier12, Angélique Grenier13,
Valérie Guérin14, Caroline Hémont15,
Anthony Léon16, Delphine Mariotte17,
Pascale Nicaise-Roland18, Martine
Pernollet19, Stéphanie Rogeau20,
Thierry Tabary21, Béatrice
Uring-Lambert22, Mylène Vivinus23,
Julien Goret1, Joana Vitte24.
1 Laboratoire d’Immunologie et Immunogénétique CHU Bordeaux, Hôpital
Pellegrin, Bordeaux, France
2 CHU Trousseau, Paris, France
3 Laboratoire d’Immunologie, Hôpital Necker-Enfants Malades, AP-HP,
Paris, France
4 Institut Fédératif de Biologie, Hôpital Purpan, CHU Toulouse,
Toulouse, France
5 Laboratoire d’Immunologie, CHU Angers, France
6 LBM CHI Toulon La Seyne sur Mer, Toulon, France
7 Département d’Immunologie, AP-HP, Hôpitaux Universitaires Paris-Sud,
Le Kremlin Bicêtre, France
8 Laboratoire d’Immunologie, CHRU Tours, Tours, France
9 Laboratoire de biochimie CHRU Besançon, Besançon, France
10 CHU Rennes, Pôle Biologie, Rennes, France
11 Service d’Immunologie, CHU Clermont-Ferrand, Clermont-Ferrand, France
12 Laboratoire d’Immunologie, Hospices Civils de Lyon, Centre
Hospitalier Lyon Sud, Pierre-Bénite, France
13 LBM Hôpital Robert Ballanger, CHI Aulnay, France
14 Laboratoire d’Immunologie, Hôpital Robert Debré, AP-HP, Paris, France
15 Laboratoire d’immunologie, CHU Nantes, Nantes, France
16 LBM CH Emile Durkheim, Epinal, France
17 Département d’Immunologie et Immunopathologie, CHU Caen, Caen, France
18 Laboratoire d’immunologie, « Autoimmunité et Hypersensibilités »,
Hôpital Bichat-Claude Bernard, AP-HP, Paris, France
19 Institut de Biologie et de Pathologie, Laboratoire d’Immunologie, CHU
Grenoble Alpes, Grenoble, France
20 CHRU de Lille, Institut d’Immunologie-HLA, Lille, France
21 Laboratoire d’immunologie, CHU Reims, Reims, France
22 Département d’Immunobiologie, Hôpitaux Universitaires de Strasbourg,
Strasbourg, France
23 Laboratoire d’Immunologie, Hôpital de l’Archet, CHU Nice, France
24 Aix Marseille Univ, IRD, University Hospitals of Marseille, MEPHI,
Marseille, France