The role of cardiac troponins (cTn) have become increasingly important in diagnosing myocardial infarction (MI), especially in patients without electrocardiogram abnormalities (1). Since the introduction of high-sensitivity (hs-)cTn immunoassays, there has been extensive clinical guidance on utilizing these biomarkers in patients with acute coronary syndromes (2). However, recommendations from a laboratory perspective were lacking until the recently reported consensus recommendation from the Academy of the American Association for Clinical Chemistry and the Task Force on Clinical Applications of Cardiac Bio-Markers of the International Federation of Clinical Chemistry and Laboratory Medicine by Wu and colleagues (3). This globally relevant expert opinion provided ten clinical laboratory practice recommendations associated with hs-cTn testing (3). These important consensus perspectives were developed to provide global consistency and knowledge in areas where formal guidance and/or data evidence was incomplete. In this Editorial, we not only acknowledge multiple recommendations as defined by Wu and co-workers, but also highlight several specific key aspects from our perspective.
Required hs-cTn guidance for clinicians
Since the launch of the first hs-cTn immunoassay (hs-cTnT, Roche), which was regulatory approved (CE Mark) outside the United States (OUS) in 2010, we recognize that the role of laboratory specialists in educating clinicians, both primary care physicians and clinical specialists, increased significantly. Guidance is predominantly required for patients with a hs-cTn concentration exceeding the MI cut-off threshold, with a rise or fall that is not that obvious, or with a negative coronary angiography. In addition, numerous (pre-)analytical factors and biological variability can lead to hs-cTn results that require guidance from clinical laboratory specialists. Although a lot of research focuses on (patho)physiological properties of cTn and its future potentials, in current clinical practice cTn are biomarkers for MI mandated by guidelines to be evaluated following a serial sampling protocol (4). As Wu et al. appropriately described, laboratory specialists should educate clinicians on the importance of specific metrics to differentiate clinically relevant hs-cTn concentration changes from analytical and biological variation. As minor hs-cTn changes can have significant clinical impact at a patient level, validating daily quality control (QC), especially at the lower analytical measuring range, is essential. These should preferably be worldwide commutable QC materials for harmonization of the different hs-cTn immunoassays leading to reduction of interassay bias.
hs-cTn cut-off values
The third universal definition of MI recommends cTn testing with a defined cut-off value based on the 99th percentile upper reference limit (URL) of a healthy population (2). Due to significant sensitivity increases in the most recent generation hs-cTn immunoassays, very low hs-cTn concentrations can be measured with excellent reproducibility [coefficient of variation (CV) smaller than 10%] (5). Unfortunately, this significant increase in assay sensitivity led to decreased clinical specificity as detectable hs-cTn concentrations can now be measured in other (non-)pathological conditions in absence of MI (6-8). In addition to multiple co-morbidities, also age and sex influence hs-cTn concentrations (9,10). Consequently, the population used to determine the 99th percentile URL should be carefully selected. Sandoval et al. provided several key recommendations and proposed that multiple surrogate biomarkers should be evaluated to define a healthy population without co-morbidities that influence hs-cTn results (11). In addition, medical history and medication usage should be taken into account and the population should be diverse with gender, age and ethnicity appropriately distributed (11). Although we acknowledge their proposal, there is thus far no global consensus on how to define the population used to determine the 99th percentile URL specifically for hs-cTn testing. A perfectly healthy population without hs-cTn influencing co-morbidities and medications will not be a representative population of patients presenting with suspected MI to the emergency department (ED). From our experience, and also reflected by variable MI cut-off values reported in literature, this resulted in a rather heterogeneous implementation of 99th percentiles across clinical laboratories, especially for cTnI (11,12). We therefore discourage clinical laboratories to individually determine their own 99th percentile cut-off threshold for MI and recommend them to adapt cut-off values derived from large cohorts in peer-reviewed literature (13-15).
Comparison of hs-cTnI and hs-cTnT
Both hs-cTnT and hs-cTnI provide high diagnostic and prognostic accuracy in patients presenting to the ED with acute chest pain (16). Therefore, both assays are considered equivalent and laboratories usually implement one hs-cTn immunoassay, which in practice predominantly depends on the clinical chemistry analyzer series used within the clinical laboratory. Nevertheless, it appeared that hs-cTnI seemed to be more prone to outliers compared to hs-cTnT (10,11,13). In addition, harmonization of hs-cTnI assays (currently strictly regulatory cleared OUS; CE Mark) is still an issue due to the heterogeneity of multiple available assays (6). Apart from analytical heterogeneity, studies conducting hs-cTn assays also highlighted possible biological differences between cTnI and cTnT (16-18). These include the diurnal rhythm of cTnT versus random fluctuation of cTnI, subtle differences in diagnostic performance and clinical decision limits that are not biologically equivalent for cTnT and cTnI (16-18).
Hs-cTnT assay characteristics
In January 2017, the United States (US) Food and Drug Administration (FDA) cleared the fifth generation cTnT assay by Roche Diagnostics and reported it to be an hs-cTnT assay. Interestingly, the US FDA prescribed assay limits that are not identical to those recommended in OUS CE marked countries. This was mainly due to the fact that different populations were used to determine their respective 99th percentile URL. The limit of blank (LoB) and limit of detection (LoD), on the other hand, were based on an identical protocol (EP17-A2) and resulted in comparable cut-offs (Table 1) (19). Additionally, the limit of quantification (LoQ) in the US is 6 ng/L as determined by FDA, while this is 13 ng/L in CE marked countries. This is explained by the fact that the US FDA defined the LoQ at the lowest concentration with a CV ≤20% in contrast to a CV ≤10% in OUS countries.
From a reporting perspective, US clinical laboratories are mandated by the FDA to apply the LoQ (CV ≤20%) as the lowest reportable value, while this is less strictly regulated for OUS clinical laboratories. Thus, a very important characteristic for OUS clinical laboratories is to define their lowest reportable hs-cTnT concentration (Table 2). Applying the LoQ would ensure that all reported results are precise, but since serial sampling is advised in European guidelines (4), we believe that especially a change in hs-cTnT is utterly relevant and therefore recommend to use the LoD (3 ng/L; e601/2) as the lowest reportable hs-cTnT concentration.
The importance of blood matrices and cTnT degradation
Solely lithium heparinized (LH) plasma is approved to be used for the hs-cTnT immunoassay in the US while several blood matrices were allowed for the fourth-generation immunoassay. Clinical centers in the US should take this into consideration when implementing or transferring to the hs-cTnT assay. Outside the US, multiple blood matrices are allowed but comparing hs-cTnT concentrations across blood matrices is discouraged when applying observation algorithms in suspected MI patients. Recent studies demonstrated altered molecular cTnT form compositions in MI patients between blood matrices with smaller molecules in serum compared to LH plasma (20). This could lead to altered assay immunoreactivity that potentially influences hs-cTnT results.
In addition to pre-analytical cTnT proteolysis, in vivo cTnT fragmentation was also observed in patients suffering from MI and ESRD patients with distinctive molecular compositions (21,22). Future research should be performed to investigate the immunoreactivity of these fragments towards the current hs-cTnT assay, but even more importantly, investigate whether specific cTnT fragments could be a target for enhanced assay specificity for MI. This was also recently recognized and suggested by other experts in the field (23,24).
Thus, although the effect of pre-analytical and/or in vivo cTnT degradation on the hs-cTnT immunoassay and their direct impact on clinical decisions still remains to be investigated, we recommend OUS clinical laboratories to standardize the blood matrix for hs-cTnT testing. In addition, we advise LH plasma to be used for the most efficient turnaround times promoting clinical decision making. Furthermore, we agree with Wu and colleagues regarding extensive documentation of (pre-)analytical variables when reporting hs-cTn values (3). This applies both in a clinical and research setting where hs-cTn values are reported.
The introduction of hs-cTn immunoassays allowed accurate assessment of hs-cTn concentrations at very low concentrations with excellent precision. Despite its outstanding diagnostic and prognostic value in MI diagnoses, the increase in assay sensitivity led to decreased clinical specificity due to (pre-)analytical and/or (patho-)physiological influences. Guidance, education, and support of clinicians by laboratory specialists will remain essential until hs-cTn specificity for MI is enhanced.
Conflicts of Interest: The authors have no conflicts of interest to declare.
- Hamm CW, Bassand JP, Agewall S, et al. ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation: The Task Force for the management of acute coronary syndromes (ACS) in patients presenting without persistent ST-segment elevation of the European Society of Cardiology (ESC). Eur Heart J 2011;32:2999-3054. [Crossref] [PubMed]
- Thygesen K, Alpert JS, Jaffe AS, et al. Third universal definition of myocardial infarction. J Am Coll Cardiol 2012;60:1581-98. [Crossref] [PubMed]
- Wu AHB, Christenson RH, Greene DN, et al. Clinical Laboratory Practice Recommendations for the Use of Cardiac Troponin in Acute Coronary Syndrome: Expert Opinion from the Academy of the American Association for Clinical Chemistry and the Task Force on Clinical Applications of Cardiac Bio-Markers of the International Federation of Clinical Chemistry and Laboratory Medicine. Clin Chem 2018. [Epub ahead of print]. [Crossref] [PubMed]
- Roffi M, Patrono C, Collet JP, et al. 2015 ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation: Task Force for the Management of Acute Coronary Syndromes in Patients Presenting without Persistent ST-Segment Elevation of the European Society of Cardiology (ESC). Eur Heart J 2016;37:267-315. [Crossref] [PubMed]
- Giannitsis E, Becker M, Kurz K, et al. High-sensitivity cardiac troponin T for early prediction of evolving non-ST-segment elevation myocardial infarction in patients with suspected acute coronary syndrome and negative troponin results on admission. Clin Chem 2010;56:642-50. [Crossref] [PubMed]
- Westermann D, Neumann JT, Sorensen NA, et al. High-sensitivity assays for troponin in patients with cardiac disease. Nat Rev Cardiol 2017;14:472-83. [Crossref] [PubMed]
- Giannitsis E, Katus HA. Cardiac troponin level elevations not related to acute coronary syndromes. Nat Rev Cardiol 2013;10:623-34. [Crossref] [PubMed]
- Gresslien T, Agewall S. Troponin and exercise. Int J Cardiol 2016;221:609-21. [Crossref] [PubMed]
- Eggers KM, Lindahl B. Impact of Sex on Cardiac Troponin Concentrations-A Critical Appraisal. Clin Chem 2017;63:1457-64. [Crossref] [PubMed]
- Kimenai DM, Henry RM, van der Kallen CJ, et al. Direct comparison of clinical decision limits for cardiac troponin T and I. Heart 2016;102:610-6. [Crossref] [PubMed]
- Sandoval Y, Apple FS. The global need to define normality: the 99th percentile value of cardiac troponin. Clin Chem 2014;60:455-62. [Crossref] [PubMed]
- Sandoval Y, Jaffe AS. Using High-Sensitivity Cardiac Troponin T for Acute Cardiac Care. Am J Med 2017;130:1358-65.e1. [Crossref] [PubMed]
- Apple FS, Ler R, Murakami MM. Determination of 19 cardiac troponin I and T assay 99th percentile values from a common presumably healthy population. Clin Chem 2012;58:1574-81. [Crossref] [PubMed]
- Gore MO, Seliger SL, Defilippi CR, et al. Age- and sex-dependent upper reference limits for the high-sensitivity cardiac troponin T assay. J Am Coll Cardiol 2014;63:1441-8. [Crossref] [PubMed]
- Krintus M, Kozinski M, Boudry P, et al. European multicenter analytical evaluation of the Abbott ARCHITECT STAT high sensitive troponin I immunoassay. Clin Chem Lab Med 2014;52:1657-65. [PubMed]
- Rubini Gimenez M, Twerenbold R, Reichlin T, et al. Direct comparison of high-sensitivity-cardiac troponin I vs. T for the early diagnosis of acute myocardial infarction. Eur Heart J 2014;35:2303-11. [Crossref] [PubMed]
- Klinkenberg LJ, van Dijk JW, Tan FE, et al. Circulating cardiac troponin T exhibits a diurnal rhythm. J Am Coll Cardiol 2014;63:1788-95. [Crossref] [PubMed]
- Wildi K, Gimenez MR, Twerenbold R, et al. Misdiagnosis of Myocardial Infarction Related to Limitations of the Current Regulatory Approach to Define Clinical Decision Values for Cardiac Troponin. Circulation 2015;131:2032-40. [Crossref] [PubMed]
- Pierson-Perry JF, Format P, Vaks JE, et al. AP17-A2: Evaluation of Detection Capability for Clinical Laboratory Measurement Procedures; Approved Guideline—Second Edition. Wayne, PA: CLSI; 2012.
- Katrukha IA, Kogan AE, Vylegzhanina AV, et al. Thrombin-Mediated Degradation of Human Cardiac Troponin T. Clin Chem 2017;63:1094-100. [Crossref] [PubMed]
- Streng AS, de Boer D, van Doorn WP, et al. Identification and Characterization of Cardiac Troponin T Fragments in Serum of Patients Suffering from Acute Myocardial Infarction. Clin Chem 2017;63:563-72. [Crossref] [PubMed]
- Mingels AM, Cardinaels EP, Broers NJ, et al. Cardiac Troponin T: Smaller Molecules in Patients with End-Stage Renal Disease than after Onset of Acute Myocardial Infarction. Clin Chem 2017;63:683-90. [Crossref] [PubMed]
- Mair J, Lindahl B, Hammarsten O, et al. How is cardiac troponin released from injured myocardium? Eur Heart J Acute Cardiovasc Care 2017. [Epub ahead of print]. [Crossref] [PubMed]
- deFilippi C, Seliger S. The Cardiac Troponin Renal Disease Diagnostic Conundrum: Past, Present, and Future. Circulation 2018;137:452-4. [Crossref] [PubMed]
Cite this article as: van Doorn WP, Vroemen WH, de Boer D, Mingels AM, Bekers O, Wodzig WK, Meex SJ. Clinical laboratory practice recommendations for high-sensitivity cardiac troponin testing. J Lab Precis Med 2018;3:30.