Clerico

A.

Franzini M

Masotti S

Passino C

Prontera C

Storti S

Zucchelli G

FRANZINI, Maria

PASSINO, Claudio

CLERICO, ALDO

MASOTTI, Silvia

Archivio della ricerca della Scuola Superiore Sant'Anna

(This is a sample cover image for this issue. The actual cover is not yet available at this time.)This article appeared in a journal published by Elsevier. The attachedcopy is furnished to the author for internal non-commercial researchand education use, including for instruction at the authors institutionand sharing with colleagues.Other uses, including reproduction and distribution, or selling orlicensing copies, or posting to personal, institutional or third partywebsites are prohibited.In most cases authors are permitted to post their version of thearticle (e.g. in Word or Tex form) to their personal website orinstitutional repository. Authors requiring further informationregarding Elsevier’s archiving and manuscript policies areencouraged to visit:http://www.elsevier.com/copyrightAuthor's personal copyLetter to the EditorEvaluation of analytical performance of a novelimmunoenzymometric assay for cTnIKeywords:cTnIcTnTHealthy subjectsCardiac markersReference valuesTo the EditorWe evaluated the analytical performance of the immuno-enzymometric assay for the cTnI, named ST AIA-PACK cTnI 3rd-Gen,using the automated AIA-2000 platform (Tosoh Corporation, Tokyo,Japan). This method is a two-site immunoenzymometric assay, whichuses a combination of twomonoclonal antibodies, respectively directedto 41–49 and 87–91 amino acids of the cTnI peptide chain, and the ter-nary troponin ITC complex as a calibration antigen [1].Blood samples from patients with cardiac diseases or healthy subjectswere collected in polypropylene tubes without or with lithium heparin.Sampleswere then rapidly centrifuged at 3000 ×g for 10 min andplasmawas then analyzed within 1 h or alternatively, stored at−80 °C.The limits of blank (LoB) and detection (LoD) for cTnI assay weredetermined according to the CLSI EP17-A protocol [2]; the calculatedLoB and LoD values were 3.5 ng/L and 8.7 ng/L, respectively. The assayreproducibility was evaluated in accordance with the CLSI EP5-A2 pro-tocol [3] by repeatedly measuring 3 heparinized plasma samples forconsecutive 20 working days with different cTnI concentrations; theresults are reported in Table 1. The between-runs imprecision proﬁlewas performed by repeatedly measuring in 20 different runs 10 hepa-rinized blood samples collected from healthy subjects and patientswith acute myocardial infarction (mean cTnI concentrations from 13to 17,782 ng/L). The calculated limits of quantitation (LoQ) at 20% CVand 10% CV were 30 and 100 ng/L of cTnI, respectively.We also evaluatedwhether themeasurement in heparinized plasmaand serum samples actually gives similar results. A very close linear re-lationship was found between the cTnI values measured in 105 serum(X-axis) and heparinized plasma (Y-axis) samples of healthy subjectsand patients with cardiac diseases (cTnI plasma=3.10+0.95 cTnIserum; R=0.999). A very close linear regression (R=0.991, n=521,y=58.3+0.602x) was found between the cTnI values measured withthe Tosoh method (Y-axis) and Access AccuTnI method (X-axis),using the UniCell DxI 800 platform (Beckman Coulter, Inc., Fullerton,USA) in 521 heparinized plasma samples of healthy subjects and cardiacpatients (Supplemental File 1). However, Tosoh method showed a meannegative bias (i.e., underestimation) of cTnI value compared to Beckman–Coulter by −30.2% (p=0.0024 by Wilcoxon signed rank test). A closecorrelation (R=0.938, n=521, y=−1067+11.6x) was also foundbetween the cTnI and cTnT values, measured with Tosoh method(X-axis) and Troponin T-hs method (Y-axis), using the automatedCobas e411 platform (Roche Diagnostics, Germany) (SupplementalFile 2).The distribution of cTnI values, measured by the Tosoh method,was evaluated in 452 healthy individuals (M 326, F 126; mean age45.6 years, median 45 years, interquartile range 33.0–58.0 years,range 17–76 years), recruited from laboratory staff, blood donors, orvoluntary subjects, included in screening programs for preventivemedicine. The presence of cardiac or systemic acute or chronic dis-eases was excluded in all subjects by history, accurate clinical exam-ination, ECG, cardiac imaging, and laboratory tests. Furthermore, allsubjects denied the use of drugs for at least two weeks before thesample collection for cTnI assay. The informed consent was obtainedby all subjects enrolled in the study and the screening programs wereapproved by the local ethical committee. The calculated 99th percentileof the cTnI values was 33 ng/L (median 9.0 ng/L, range 0–44 ng/L). Thepercentages of healthy population with values equal or less than LOB(3.5 ng/L) and LOD (8.7 ng/L) valueswere 15.7% and 49.8%, respectively.Quality speciﬁcations [4,5] for troponin measurement recommendan assay imprecision ≤10% CV for the values corresponding to the99th percentile of reference population. Use of troponin assays withintermediate imprecision (from 10% to 20% CV) at the 99th percentile,however, does not lead to signiﬁcant patient misclassiﬁcation, wheninterpreting serial troponin results [4,5].Compared to previous second-generation AIA-Pack assay [4], thethird-generation AIA-Pack assay for cTnI showed an improved analyt-ical sensitivity and reproducibility, especially at very low cTnI concen-trations. Indeed, the LoD and 10% LoQ values of the second-generationassay, as reported in a previous study [1], were 38 ng/L and130 ng/L, re-spectively,while the corresponding values of the third-generation assay,as assessed in the present study, were 8.7 ng/L and 100 ng/L. This im-proved imprecision at lower cTnI concentrations allows the measure-ment of the 99th percentile of reference population (i.e., 33 ng/L) withan imprecision less than 20%, as well as the detection with conﬁdence(measured values above the LoD) of cTnI circulating levels in morethan half of normal subjects. These analytical performances suggestthat the third-generation AIA-Pack Tosoh assay for cTnI should be con-sidered as “clinically acceptable”, according to the scorecard proposedby Apple [4].The third-generation AIA-Pack Tosoh assay for cTnI showed a veryclose agreement throughout all the working range with the AccessAccuTnI Beckam–Coulter method, used for the routine measurementof cTnI in the Authors' laboratory (Supplemental File 1). Moreover, aClinica Chimica Acta 416 (2013) 48–49Table 1Evaluation of assay reproducibility according to the CLSI EP5-A2 protocol.Sample n Mean cTnI concentration (ng/L) Within-run CV (%) Total CV (%)A 20 22 19.62 35.46B 20 52 9.14 18.42C 20 119 4.00 6.500009-8981/$ – see front matter © 2012 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cca.2012.11.018Contents lists available at SciVerse ScienceDirectClinica Chimica Actaj ourna l homepage: www.e lsev ie r .com/ locate /c l inch imAuthor's personal copyclose agreement was also demonstrated between the cTnI measuredby Tosoh methods and those of cTnT measured with ECLIA Rochemethod (Supplemental File 2). These data suggest that the third-generation AIA-Pack assay is suitable for the clinical evaluation ofpatients with cardiac diseases.SponsorshipTosoh Europe N.V. (Tessenderlo, Belgium) kindly supplied allreagents and calibrators used in the study for the measurement ofcTni with AIA-1000 platform.Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.cca.2012.11.018.References[1] Pagani F, Steﬁni F, Toppino M, et al. Multicenter evaluation of the TOSOH AIA-Packsecond-generation cardiac troponin I assay. Clin Chem 2004;50:1707–9.[2] CLSI EP17-A protocol. Protocols for determination of limits of detection and limitsof quantitation; approved guidelines, vol. 24, No. 34; 2004 [Wayne, Pennsylvania].[3] CLSI EP5-A2 protocol. Evaluation of precision performance of quantitative mea-surement methods, vol. 24, No. 25. Approved guideline, Second edition; 2004[Wayne, Pennsylvania].[4] Apple FS. A new season for cardiac troponin assays: it's time to keep a scorecard.Clin Chem 2009;55:1303–6.[5] Apple FS, Collinson PO. IFCC Task Force on Clinical Applications of Cardiac Biomarkers.Analytical characteristics of high-sensitivity cardiac troponin assays. Clin Chem2012;58:54–61.Maria FranziniFondazione Toscana G. Monasterio, Pisa, ItalyScuola Superiore Sant'Anna, Pisa, ItalyConcetta PronteraSilvia MasottiFondazione Toscana G. Monasterio, Pisa, ItalyGiancarlo ZucchelliQualiMedLab, Pisa, ItalySimona StortiFondazione Toscana G. Monasterio, Pisa, ItalyClaudio PassinoAldo Clerico⁎Fondazione Toscana G. Monasterio, Pisa, ItalyScuola Superiore Sant'Anna, Pisa, Italy⁎Corresponding author at: Department of Laboratory Medicine,Fondazione CNR-Regione Toscana G. Monasterio,Scuola Superiore Sant'Anna, Via Trieste 41, 56126 Pisa, Italy.Tel.: +39 0585 493569; fax: +39 0585 493601.E-mail address: clerico@ifc.cnr.it (A. Clerico).2 November 201249Letter to the Editor

Evaluation of analytical performance of a novel immunoenzymometric assay for cTnI.

Evaluation of analytical performance of a novel immunoenzymometric assay for cTnI.

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