Elsevier

Clinica Chimica Acta

Volume 412, Issues 3–4, 30 January 2011, Pages 370-375
Clinica Chimica Acta

Clinical performance of a new point-of-care cardiac troponin I assay compared to three laboratory troponin assays

https://doi.org/10.1016/j.cca.2010.11.015Get rights and content

Abstract

Background

Studies of cardiac markers in diagnosing acute myocardial infarction (AMI) have mostly been performed using central laboratory platforms. The AQT90 FLEX TnI (troponin I) assay is designed for quantitative point of care testing (POCT). This study evaluated clinical performance in diagnosing AMI of the AQT90 FLEX TnI POCT assay compared with central laboratory troponin assays.

Methods

The study included 458 chest pain patients. Blood samples were obtained on admission and after 6–9 h. Blood was analyzed using the following assays: AQT90 FLEX TnI, Access AccuTnI, Abbott AxSYM ADV, Roche cTnT, Roche CKMBmass. Patients were diagnosed with AMI according to the new universal definition of AMI.

Results

The performance of the AQT90 FLEX TnI assay on admission was equivalent to the Abbott AxSYM ADV cTnI but inferior to the AccuTnI. After 6–9 h both laboratory based assays were superior. The AQT90 FLEX TnI had a negative predictive value (NPV) of 90 and 96% (admission; 6–9 h). No statistical differences were seen in receiver operating characteristics analysis.

Conclusions

The AQT90 FLEX TnI POCT assay was marginally inferior to the two laboratory based assays of cTnI in diagnosing AMI. A high (NPV) may make this assay suitable as a rule out marker.

Introduction

Measurement of cardiac troponins I and T (cTnI and cTnT) in blood is currently the recommendation for the biochemical identification of patients with myocardial cell injury and AMI [1], [2]. It has recently been shown that the new assays of cTnI and cTnT may be even more sensitive than the previous assays of cTnT (4th generation) early in acute coronary syndrome (ACS) [3], [4], [5], [6]. The introduction of new sensitive assays has led to increased interest in exploring the value of cTnI and cTnT in the acute setting and in particular as point-of care test (POCT) assays.

The cTnI assay developed for the AQT90 FLEX platform (Radiometer Medical ApS, Denmark) is a POCT assay designed to provide a high clinical performance together with a fast turn around time (TAT) with an analytical run time of approximately 18 min. AQT90 FLEX is a random-access point-of-care analyzer intended for the quantitative determination of cardiac, coagulation, and sepsis markers in whole blood or plasma [7].

Current guidelines recommend that that the 99th percentile of the upper reference limit (URL) should be used as a cut-off for the diagnosis of acute myocardial infarction (AMI) [2], [8], given a coefficient of variation (CV) of ≤ 10% at the 99th percentile URL.

The aim of this study was to evaluate the clinical performances of a new POCT assay, the cardiac specific AQT90 FLEX TnI, and to compare it with two sensitive laboratory assays of cTnI, i.e. the Beckman Coulter AccuTnI assay and the Abbott AxSYM ADV assay, as well as the Roche cTnT (4th generation) laboratory assay.

Section snippets

Patient specimens

The study population comprised 458 subjects who were admitted with chest pain and suspected of ACS. The study population included 293 males (64%) and 165 females (36%). Patients were referred by a general practitioner or the ambulance service. They were subsequently admitted and included by the physician on duty. Patients admitted more than once during the investigation period were only included on their first admission. Twelve lead electrocardiogram (ECG-12) was performed in all patients.

Routine diagnostic procedures

At

Results

Of the 458 patients referred with chest-pain, 104 patients (23%) had a final diagnosis of AMI according to the above mentioned criteria. Of these, two patients (1.9%) developed ST segment elevations in the ECG and subsequently went to acute revascularization. The median time fron symptoms onset to the first blood sample was 2.2 h.

Table 1 shows baseline characteristics of the population.

Three assays of cTnI were compared (AQT90 FLEX TnI — designed for quantitative POC testing; Access AccuTnI and

Discussion

Our comparison of three different assays of cTnI against a diagnosis of AMI verified by current diagnostic criteria [2] shows that the three assays behave equally well and with a high degree of sensitivity and specificity. There is a high concordance between the three cTnI assays. Previous studies have showed a low concordance between the Abbott Architect cTnI (which shares antibody configuration with the AxSYM ADV assay used in this study) and the Roche cTnT assays with significantly more

Limitations

The study compares a POC test with laboratory based assays of troponins, and it can therefore be considered a limitation that collection of blood samples and analysis on the AQT90 FLEX instrument was performed by trained laboratory staff and not the staff in the emergency department. Second, one may question that heparinised plasma and not whole blood was used for the POC test. However, the manufacturer authorizes the use of both kinds of specimens without changes in reference values [32].

Conclusion

This study shows that diagnostic performance on admission, with respect to the diagnosis of AMI, of the POCT based AQT90 FLEX TnI was equivalent to the Abbott AxSYM ADV cTnI assay, but inferior to the AccuTnI assay. After 6–9 h, both the central laboratory based assays were superior compared to the AQT90 FLEX TnI POCT assay. The negative predictive value was high for the AQT90 FLEX TnI assay on admission making the assay suitable as a possible rule out marker in the POCT setting. However, this

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    Grant support assays and reagents were kindly provided by Abbott Diagnostics, Denmark, Radiometer Medical, Denmark, and Roche Diagnostics, Denmark.

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