Jump to ContentJump to Main Navigation
Show Summary Details
More options …

Diagnosis

Official Journal of the Society to Improve Diagnosis in Medicine (SIDM)

Editor-in-Chief: Graber, Mark L. / Plebani, Mario

Ed. by Argy, Nicolas / Epner, Paul L. / Lippi, Giuseppe / McDonald, Kathryn / Singh, Hardeep

Editorial Board: Basso , Daniela / Crock, Carmel / Croskerry, Pat / Dhaliwal, Gurpreet / Ely, John / Giannitsis, Evangelos / Katus, Hugo A. / Laposata, Michael / Lyratzopoulos, Yoryos / Maude, Jason / Newman-Toker, David / Singhal, Geeta / Sittig, Dean F. / Sonntag, Oswald / Zwaan, Laura

4 Issues per year

Online
ISSN
2194-802X
See all formats and pricing
More options …

Analytical assessment of the Beckman Coulter Unicel DxI AccuTnI+3 immunoassay

Giuseppe Lippi / Mariella Dipalo / Paola Avanzini / Alessandro Formentini
  • Service of Transfusion Medicine and Immunohematology, Academic Hospital of Parma, Parma, Italy
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Rosalia Aloe
Published Online: 2014-02-27 | DOI: https://doi.org/10.1515/dx-2013-0039

To the Editor,

The diagnostics of myocardial injury and, especially, of ischemic heart disease strongly relays upon laboratory data [1]. In particular, the assessment of cardiospecific troponin(s) is now almost unavoidable in clinical practice, as for current guidelines and recommendations [2]. It is also noteworthy, however, that specific criteria have been defined for characterising and classifying the different troponin immunoassays that are currently available in the market. These specifically include the calculation of the limit of blank (LOB; i.e., the highest value expectable in replicates of samples containing no analyte), the limit of detection (LOD; i.e., the lowest amount of analyte that can be detected in a sample) [3], the value characterized by optimal imprecision (i.e., coefficient of variation [CV] of 10% or lower), along with the 99th percentile of the upper reference limit (URL) of a reference population of presumably healthy subjects [4, 5].

In a previous article, Zaninotto et al. assessed the analytical performance of the Beckman Coulter AccuTnI (Beckman Coulter, Brea, CA, USA) immunoassay on both Beckman Coulter Unicel DxI and Beckman Coulter Access-2 [6]. In two following investigations, it has then been reported that this method [7, 8], but not its prototype high-sensitivity evolution which is not commercially available so far [9], may suffer from problems of carryover that may ultimately bias test results. To overcome this drawback, the manufacturer has recently released an evolution of this assay that would make it more resistant against carry-over. The processing of reagent material has also been improved, thus resulting in better to lot-to-lot consistency of AccuTnI+3 assay reagents. Therefore, the aim of this study (performed between December the 2nd and the 12th, 2013) was the analytical evaluation of the novel AccuTnI+3 on Unicel DxI, along with evaluation of carry-over.

The detailed characteristics of this immunoassay have been earlier described by Zaninotto et al. in a previous publication [6]. In brief, Unicel DxI AccuTnI is a two-site chemiluminescent immunoassay employing mouse monoclonal anti-human troponin I (TnI) antibody-alkaline phosphatase conjugate and paramagnetic particles coated with mouse monoclonal anti-human TnI antibody. The main differences of this novel version of the immunoassay consist in modifications to the calibrator value assignment to harmonize data of Unicel DxI with those of Access-2, implementation of an algorithm to adjust results for changes in room temperature, along with modifications to the assay protocol file for improvement of mixing and probe wash process.

As regards the analytical evaluation of AccuTnI+3, the value associated with optimal imprecision was calculated by preparation of serial dilutions (i.e., 1:2; 1:4; 1:8 and 1:16) of an EDTA plasma sample with a TnI concentration of 120 ng/L and an EDTA plasma sample with undetectable TnI, 10 replicated measurements of each dilution, calculation of the CV for each dilution and creation of a model fit to estimate the TnI value with 10% CV. The LOB was calculated as the value corresponding to the sum of the mean and the 1.645*standard deviation (SD) of 20 replicates of saline tested in one single run, as for Clinical and Laboratory Standards Institute (CLSI) recommendations [3]. The LOD was calculated as the sum of the LOB and 1.645*SD of 20 replicates of an EDTA plasma sample with the lowest measurable value of TnI, as estimated from the study for calculation of the 10% CV value [3]. The 99th percentile was calculated using 125 EDTA plasma samples obtained from healthy Caucasian blood donors (77 males and 48 females, age range 21–54 years), according to the recommendations of the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) and the CLSI [10]. No subjects had current or past history of ischemic heart disease, cardiac-related medical conditions or non-cardiac-related diseases as established by a health questionnaire. The carryover was calculated testing the sequence A1-A2-B1-B2-B3 and using Broughton’s formula (carryover, %=100×[B1−B3]/[A2−B3]), where A was an EDTA plasma specimen with a very high TnI concentration (i.e., 484,176 ng/L, final value obtained after 1:50 dilution with a TnI negative sample), and B was an EDTA plasma sample with a TnI value close to the diagnostic cut-off (i.e., 60 ng/L) [11]. The study was based on pre-existing EDTA plasma samples obtained after routine analysis was completed and no informed consent or Ethics Committee approval were hence necessary. The investigation was however performed in accord with the Declaration of Helsinki and under the terms of all relevant local legislation. The statistical analysis was performed with Analyse-it (Analyse-it Software Ltd, Leeds, UK).

According to the study protocol described earlier, the value corresponding to 10% CV was 37 ng/L, and thereby lower than that previously reported for the former assay on the same analytical platform (i.e., 58 ng/L) (Figure 1). We also obtained a value of 9 ng/L for the LOB and a value of 13 ng/L for the LOD for the new AccuTnI+3, respectively. The LOD was hence globally comparable to that earlier found for the former method (i.e., 12 ng/mL). The 99th percentile URL calculated from our local population of healthy blood donors was 30 ng/L (95% CI, 26–35 ng/L), and thus virtually identical to that estimated with the former Unicel DxI AccuTnI commercial assay (i.e., 34 ng/L; 95% CI, 95% CI, 30–41 ng/mL). Nevertheless, the number of measurable values (i.e., ≥9 ng/L) obtained in our presumably healthy population with AccuTnI+3 was lower (i.e., 13%) than that reported for the former assay (i.e., 42%). It is noteworthy, however, that 125 individuals may be not sufficient for a reliable determination of the 99th percentile URL, and we can hence conclude that we have performed a rough validation of this threshold with some degrees of uncertainty. Finally, the carry-over was both analytically and clinically negligible with AccuTnI+3, as attested by the very low value (i.e., 0.004%) and the modest percentage bias, which remained lower than the 50% variation that is currently recommended for diagnosing ischemic heart disease during serial testing (80 ng/L in aliquot B1 vs. 60 ng/L in aliquot B3, i.e., 33% increase).

Calculation of troponin I value with 10% coefficient of variation (CV) for Beckman Coulter Unicel DxI AccuTnI+3.
Figure 1

Calculation of troponin I value with 10% coefficient of variation (CV) for Beckman Coulter Unicel DxI AccuTnI+3.

In conclusions, the results of this study attest that the Unicel DxI Accu-TnI+3 immunoassay display an analytical performance that is globally comparable to that of the earlier method, except for an approx. 40% lower TnI value associated with 10% CV. It is also noteworthy that the problem of carry-over that seemed to afflict the former method was apparently eliminated after development of this evolution of the assay.

References

  • 1.

    Lackner KJ. Laboratory diagnostics of myocardial infarction–troponins and beyond. Clin Chem Lab Med 2013;51:83–9.Web of ScienceGoogle Scholar

  • 2.

    Casagranda I, Cavazza M, Clerico A, Galvani M, Ottani F, Zaninotto M, et al. Proposal for the use in emergency departments of cardiac troponins measured with the latest generation methods in patients with suspected acute coronary syndrome without persistent ST-segment elevation. Clin Chem Lab Med 2013;51:1727–37.Web of ScienceGoogle Scholar

  • 3.

    Clinical and Laboratory Standards Institute. Protocols for Determination of Limits of Detection and Limits of Quantitation; Approved Guideline. CLSI document EP17-A. Wayne, PA: Clinical and Laboratory Standards Institute; 2004.Google Scholar

  • 4.

    Lippi G, Cervellin G. Do we really need high-sensitivity troponin immunoassays in the emergency department? Maybe not. Clin Chem Lab Med 2014;52:205–12Web of ScienceGoogle Scholar

  • 5.

    Lackner KJ. Do we really need high-sensitive troponin immunoassays in the emergency department? Definitely, yes! Clin Chem Lab Med 2014;52:201–4.Web of ScienceGoogle Scholar

  • 6.

    Zaninotto M, Mion MM, Novello E, Moretti M, Delprete E, Rocchi MB, et al. Precision performance at low levels and 99th percentile concentration of the Access AccuTnl assay on two different platforms. Clin Chem Lab Med 2009;47: 367–71.Google Scholar

  • 7.

    Dimeski G, Jones B, Brown N. Carryover can be a cause of false-positive results with the Beckman AccuTnI assay. Clin Chem Lab Med 2012;50:1135–6.CrossrefWeb of ScienceGoogle Scholar

  • 8.

    Gould MJ, Wilgen U, Pretorius CJ. Probing indiscretions: contamination of cardiac troponin reagent by very high patient samples causes false-positive results. Ann Clin Biochem 2012;49(Pt 4): 395–8.Web of ScienceGoogle Scholar

  • 9.

    Lippi G, Avanzini P, Musa R, Aloe R, Cervellin G. Carryover does not affect results of Beckman Coulter highly-sensitive-AccuTnI assay on Access 2. Clin Chem Lab Med 2013;51:e141–3.Web of ScienceGoogle Scholar

  • 10.

    Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline – Third Edition. CLSI document C28-A3. Wayne, PA: Clinical and Laboratory Standards Institute; 2008.Google Scholar

  • 11.

    Broughton PM. Carry-over in automatic analysers. J Automat Chem 1984;6:94–5.Google Scholar

About the article

Corresponding author: Prof. Giuseppe Lippi, Laboratory of Clinical Chemistry and Hematology, U.O. Diagnostica Ematochimica, Azienda Ospedaliero-Universitaria di Parma, Via Gramsci, 14, 43126 – Parma, Italy, Phone: +0039-0521-703050, +0039-0521-703791, E-mail: ,


Received: 2013-12-20

Accepted: 2014-01-30

Published Online: 2014-02-27

Published in Print: 2014-06-01


Conflict of interest statement

Authors’ conflict of interest disclosure: The authors stated that there are no conflicts of interest regarding the publication of this article.

Research funding: None declared.

Employment or leadership: None declared.

Honorarium: None declared.


Citation Information: Diagnosis, Volume 1, Issue 2, Pages 195–197, ISSN (Online) 2194-802X, ISSN (Print) 2194-8011, DOI: https://doi.org/10.1515/dx-2013-0039.

Export Citation

©2014 by Walter de Gruyter Berlin/Boston. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License. BY-NC-ND 3.0

Citing Articles

Here you can find all Crossref-listed publications in which this article is cited. If you would like to receive automatic email messages as soon as this article is cited in other publications, simply activate the “Citation Alert” on the top of this page.

[1]
Urs Wilgen, Carel J Pretorius, Michael J Gould, and Jacobus PJ Ungerer
Annals of Clinical Biochemistry, 2016, Volume 53, Number 1, Page 177
[2]
Dae-Hyun Ko, Tae-Dong Jeong, Eun-Jung Cho, Jinsook Lim, Misuk Ji, Kyunghoon Lee, Woochang Lee, Yeo-Min Yun, Sail Chun, Junghan Song, Kye-Chul Kwon, and Won-Ki Min
Clinica Chimica Acta, 2017, Volume 464, Page 1
[3]
Giuseppe Lippi, Ruggero Buonocore, Fabio Schirosa, and Gianfranco Cervellin
International Journal of Cardiology, 2015, Volume 194, Page 68
[4]
Gianfranco Cervellin, Ivan Comelli, Gianni Rastelli, Alessandra Picanza, and Giuseppe Lippi
Clinical Biochemistry, 2014, Volume 47, Number 18, Page 298

Comments (0)

Please log in or register to comment.
Log in