Investigating outlier rates of cardiac troponin I and troponin T assays: A systematic review

Objectives

This review aimed to harmoniously summarize and compare outlier rates for various cardiac troponin (cTn) assays, including high-sensitivity-cTn (hs-cTn) assays and contemporary cTn (generation of assays prior to hs-cTn ones) assays, from the published studies.

Methods

The PRISMA guidelines were utilized to perform this systematic review. Five databases, including PubMed, Scopus, Embase, Cochrane Library, and Web of Science, were searched using specific keywords up to June 30th, 2023. Studies reporting specifically calculated outlier rates for cTn assays when conducting in-vitro diagnosis in human samples were included. Selected studies were then further assessed using the GRADE tool.

Results

Thirteen studies were included. The data from the studies were summarized statistically in this review. The results showed substantial evidence of improved analytical robustness or reduced respective mean rates of outliers, critical outliers, and analytical outliers for hs-cTn assays (0.14 %, 0.18 %, and 0.18 %) compared to contemporary cTn assays (0.63 %, 0.71 %, and 0.50 %).

Conclusion

The findings offer promisingly provide a comprehensive reference for laboratory scientists and clinical staff in choosing the most suitable cTn assay for patient care regrading outlier rates. Besides, this review reveals the advancements of hs-cTn assays with lower outlier rates than contemporary cTn assays. The emerging challenges for continuously improving analytical robustness of cTn assays are also elaborated.

The underestimated issue of non-reproducible cardiac troponin I and T results: case series and systematic review of the literature

Cardiac troponins (cTn) are the preferred biomarkers for the evaluation of myocardial injury and play a key role in the diagnosis of acute myocardial infarction (MI). Pre-analytical or analytical issues and interferences affecting troponin T and I assays are therefore of major concern given the risk of misdiagnosis. False positive troponin results have been related to various interferences including anti-troponin antibodies, heterophilic antibodies, or elevated alkaline phosphatase level. On the other hand, false negative results have been reported in the case of a large biotin intake. These interferences are characterized with erroneous but reproducible troponin results. Of interest, non-reproducible results have also been reported in the literature. In other words, if the sample is reanalyzed a second time, a significant difference in troponin results will be observed. These interferences have been named "fliers" or "outliers". Compared to the biotin interference that received major attention in the literature, troponin outliers are also able to induce harmful clinical consequences for the patient. Moreover, the prevalence of outliers in recent studies was found to be higher (0.28-0.57%) compared to the biotin interference. The aim of this systematic review is to warn clinicians about these non-reproducible results that may alter their clinical judgment. Four case reports that occurred in the Clinique of Saint-Luc Bouge are presented to attest this point. Moreover, we aimed at identifying the nature of these non-reproducible troponin results, determining their occurrence, and describing the best way for their identification.

Transitioning high sensitivity cardiac troponin I (hs-cTnI) into routine diagnostic use: More than just a sensitivity issue

OBJECTIVES

High sensitivity cardiac troponin T and I (hs-cTnT and hs-cTnI) assays show analytical, diagnostic and prognostic improvement over contemporary sensitive cTn assays. However, given the importance of troponin in the diagnosis of myocardial infarction, implementing this test requires rigorous analytical and clinical verification across the total testing pathway. This was the aim of this study.

DESIGN AND METHODS

Analytical verification included assessment of critical outlier frequency, for hs-cTnI and cTnI assays. Concordance for paired cTnI and hs-cTnI measurements (n=1096) was verified using 99th percentiles for both genders (cTnI: 30 ng/L, hs-cTnI: 25 ng/L) and for men and women separately (hs-cTnI: M: 34;F: 16 ng/L). Discordant data was correlated with clinical and laboratory information. Diagnosis of Acute Coronary Syndrome (ACS) or Non-ACS was adjudicated by two cardiologists independently.

RESULTS

The hs-cTnI assay showed a lower (10-fold) critical outlier rate (0.091%) and more detectable results above the limit of detection (LOD) (23.4%) and 99th percentile (2.4%), compared to cTnI. Analytical concordance between the two assays was high (94.5%) but decreased (91.7%) when gender-specific hs-cTnI cut-offs were used. The hs-cTnI assay gave fewer false negatives (up to 1.0%) but disproportionately more false positives (up to 6.7%) overall, which improved (3.9%) for serial measurements.

CONCLUSIONS

Laboratories should analytically and clinically verify hs-cTn assays before use, with attention to performance and the clinical and diagnostic algorithms that support appropriate testing and result interpretation. Work in the pre- and post-analytical phases is necessary to augment the analytical improvement in the new era of troponin testing.

A practical approach for the validation and clinical implementation of a high-sensitivity cardiac troponin I assay across a North American city

Objectives

Despite several publications on the analytical performance of high-sensitivity cardiac troponin (hs-cTn) assays, there has been little information on how laboratories should validate and implement these assays into clinical service. Our study provides a practical approach for the validation and implementation of a hs-cTn assay across a large North American City.

Design and methods

Validation for the Abbott ARCHITECT hs-cTnI assay (across 5 analyzers) consisted of verification of limit of blank (LoB), precision (i.e., coefficient of variation; CV) testing at the reported limit of detection (LoD) and within and outside the 99th percentile, linearity testing, cTnI versus hs-cTnI patient comparison within and between analyzers (Passing and Bablok and non-parametric analyses). Education, clinical communications, and memorandums were issued in advance to inform all staff across the city as well as a selected reminder the day before live-date to important users. All hospitals switched to the hs-cTnI assay concurrently (the contemporary cTnI assay removed) with laboratory staff instructed to repeat samples previously measured with the contemporary cTnI assay with the hs-cTnI assay only by physician request.

Results

Across the 5 analyzers and 6 reagent packs the overall LoB was 0.6 ng/L (n=60) with a CV of 33% at an overall mean of 1.2 ng/L (n=60; reported LoD=1.0 ng/L), with linearity demonstrated from 45,005 ng/L to 1.1 ng/L. Precision testing with a normal patient-pool QC material (mean range across 5 analyzers was 3.9–4.4 ng/L) yielded a range of CVs from 7% to 10% (within-run) and CVs from 7% to 18% (between-run) with the high patient-pool QC material (mean range across 5 analyzers was 29.6–36.3 ng/L) yielding a range of CVs from 2% to 5% (within-run) and CVs from 4% to 8% (between-run). There was agreement between hs-cTnI versus cTnI with the patient samples (slope ranges: 0.89–1.03; intercept ranges: 1.9–3.8 ng/L), however, the median CV on patient samples <100 ng/L across the analyzers was 5.6% for hs-cTnI versus 18.7% for the contemporary assay (p<0.001). Following the switch to hs-cTnI testing, no requests for repeat measurements were received.

Conclusions

Validation and implementation of hs-cTnI testing across multiple sites requires collaboration within the laboratories and between hospital laboratories and clinical staff.

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City-wide analytical validation of a high-sensitivity cardiac troponin assay.

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Practical approach to hs-cTnI validation and clinical implementation.

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Clinical support and communication are important for a successful implementation.

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New QC practices and comparability testing for hs-cTnI monitoring.