Serial cardiac troponin differences measured on four contemporary analyzers: Relative differences, actual differences and reference change values compared

Evaluation of the Atellica TnIH cardiac troponin I assay and assessment of biological equivalence

OBJECTIVES

We evaluated the analytical performance characteristics and the biological equivalence of the Atellica TnIH assay.

METHODS

Precision, detection capability, linearity, and sex specific 99^th percentiles were determined de novo. Classification of patients relative to the 99^th percentiles was used to assess biological equivalence.

RESULTS

Analytical precision and detection capability of the Atellica TnIH assay is excellent with a limit of blank <1 ng/L and 62.5% of women and 93% of men had results above the limit of detection. The 99th percentiles (90% CI) in women were 49 ng/L (31-67) and 70 ng/L (48-121) in men. An asymmetrical distribution involving 5% of results was notable. Agreement was moderate (Kappa 0.58, 95% CI 0.53-0.63) with 20% of patients discordantly classified with Atellica TnIH below and Access hsTnI above the 99th percentiles. Serial results in 195 patients demonstrated good agreement (Kappa 0.84, 95% CI 0.77-0.90). Differences greater than the assay specific reference change values (z_≥±1.96) occurred in 65% (95% CI 53-76%) of 99th percentile discordant patients compared to 2.7% (p<0.001) and 76% (p=0.17) of the concordant low and high cTnI groups respectively.

CONCLUSIONS

The 99th percentile discordant and the concordantly elevated groups are more alike with respect to their z_≥±1.96 rates. This favours an overestimated Atellica TnIH 99th percentile as more likely, and we hypothesize that antibody interference resulting in asymmetric scatter of nearly 5% samples may be the underlying mechanism. Analytical accuracy and interferences in cardiac troponin assays should be investigated and resolved with high priority.

Troponin least significant change (z-score) is associated with poor clinical outcomes in patients presenting to the emergency department

BACKGROUND

A rise and/or fall in high sensitivity cardiac troponin (hs-Tn) is critical in defining acute myocardial injury and therefore the diagnosis of acute myocardial infarction. A significant rise in hs-Tn is not well defined in current guidelines. Calculation of a z-score for two consecutive hs-Tn measurements is a method-independent measure of dynamic troponin elevation. However, the association of hs-Tn z-score with outcomes for unselected emergency department admissions is unknown. Moreover, the association of non-dynamic troponin elevations, as defined by a normal z-score, with clinical outcomes remains to be assessed.

METHODS

We retrospectively calculated z-scores for patients presenting to emergency department over 18 months who had serial troponin measurements with at least one result >99th percentile using the Abbott hs-TnI assay. We assessed the association of z-score with discharge diagnosis, cardiac interventions, inpatient mortality, length of stay and readmission rates.

RESULTS

There were 2062 presentations for 1830 patients where a z-score was calculated. Z-score was elevated in 1080 presentations. Dynamic troponin elevation (z-score ≥ 2) was associated with acute myocardial infarction (OR = 9.1, P < 0.01), admission to an inpatient unit (95 vs. 88%, P < 0.01), increased inpatient length of stay (97 vs. 65 days, P < 0.01), inpatient coronary intervention (21 vs. 6%, P < 0.01) and mortality (4.4 vs. 2.4%, P < 0.05) compared with myocardial injury with a static troponin elevation.

CONCLUSIONS

Z-score is an assay-independent tool to alert clinicians of significant, dynamic troponin elevation and acute myocardial injury. It is associated with poorer clinical outcomes.

Clinical relevance of biological variation of cardiac troponins

The high-sensitivity immunoassays for cardiac troponin I (hs-cTnI) and cardiac troponin T (hs-cTnT) are recommended by all the most recent international guidelines as gold standard laboratory methods for the detection of myocardial injury and diagnosis of acute myocardial infarction (AMI). In this review article, the Authors aimed at discussing the relevant biochemical, physiological, and clinical issues related to biological variability of cTnI and cTnT. Cardiac troponins, measured with hs-cTn methods, show a better clinical profile than the other cardio-specific biomarkers (such as the natriuretic peptides, BNP and NT-proBNP). In particular, the hs-cTn methods are characterized by a low intra-individual index of variation (<0.6) and reduced analytical imprecision (about 5% CV) at the clinical cut-off value (i.e., the 99th percentile URL value). Moreover, recent studies have reported that differences between two hs-cTn measured values (RCV) >30% can be considered statistically significant. These favourable biological characteristics and analytical performance of hs-cTn methods significantly improved the accuracy in the diagnostic process of acute coronary syndromes (ACS) in patients admitted to emergence department. In addition, several studies have demonstrated the clinical usefulness of cardiovascular risk evaluation with hs-cTn methods in some groups of patients with clinical conditions at high cardiovascular risk (such as systemic hypertension, severe obesity, diabetes mellitus, renal insufficiency, and chronic obstructive pulmonary disease). However, screening programs in the general population with hs-cTn methods for cardiovascular risk stratification require further investigation to define the optimal target populations, timing of measurement, and preventive interventions.

A comparison of cardiac troponin T delta change methods and the importance of the clinical context in the assessment of acute coronary syndrome

Background

The management of patients presenting with symptoms suggestive of acute coronary syndrome is a significant challenge for clinicians. Guidelines for the diagnosis of acute myocardial infarction require a rise and/or fall of cardiac troponin, along with other criteria. Knowing what constitutes a significant delta change from baseline is still unclear and the literature is varied.

Methods

We compared three methods for determining cardiac troponin delta changes (relative, absolute and z-scores) for detecting acute myocardial infarction in 806 patients presenting to an emergency department with symptoms suggestive of acute coronary syndrome. Blood specimens were collected at admission and 2, 3, 4 and 6 h postadmission and tested on the Roche Elecsys high-sensitivity troponin T assay.

Results

A positive diagnosis for acute myocardial infarction was found in 39 (4.8%) patients. ROC AUC showed better performance for the absolute and z-score delta change (0.959–0.988 and 0.956–0.988, respectively) compared with relative delta change (0.921–0.960) at all time points in the diagnosis of acute myocardial infarction. Optimal timing for the second sample was at 4–6 h postadmission.

Conclusions

Although not statistically significant, the results show a trend of absolute and z-score delta change performing better than relative delta change for the diagnosis of acute myocardial infarction. The z-score approach allows for a single cut-off value across multiple high-sensitivity assays which could be useful in the clinical setting. Our study also highlighted the importance of interpreting cardiac troponin changes in the clinical context with a combination of the patient’s clinical history and electrocardiogram.

Determination of age- and sex-specific 99th percentiles for high-sensitive troponin T from patients: an analytical imprecision- and partitioning-based approach

BACKGROUND

Detection of acute myocardial infarction (AMI) is mainly based on a rise of cardiac troponin with at least one value above the 99th percentile upper reference limit (99th URL). However, circulating high-sensitive cardiac troponin T (hs-cTnT) concentrations depend on age, sex and renal function. Using an analytical imprecision-based approach, we aimed to determine age- and sex-specific hs-cTnT 99th URLs for patients without chronic kidney disease (CKD).

METHODS

A 3.8-year retrospective analysis of a hospital laboratory database allowed the selection of adult patients with concomitant plasma hs-cTnT (<300 ng/L) and creatinine concentrations, both assayed twice within 72 h with at least 3 h between measurements. Absence of AMI was assumed when the variation between serial hs-cTnT values was below the adjusted-analytical change limit calculated according to the inverse polynomial regression of analytical imprecision. Specific URLs were determined using Clinical and Laboratory Standards Institute (CLSI) methods, and partitioning was tested using the proportion method, after adjustment for unequal prevalences.

RESULTS

After outlier removal (men: 8.7%; women: 6.6%), 1414 men and 1082 women with estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2 were assumed as non-AMI. Partitioning into age groups of 18-50, 51-70 and 71-98 years, the hs-cTnT 99th URLs adjusted on French prevalence were 18, 33, 66 and 16, 30, 84 ng/L for men and women, respectively. Age-partitioning was clearly required. However, sex-partitioning was not justified for subjects aged 18-50 and 51-70 years for whom a common hs-cTnT 99th URLs of about 17 and 31 ng/L could be used.

CONCLUSIONS

Based on a laboratory approach, this study supports the need for age-specific hs-cTnT 99th URLs.

High-sensitivity cardiac troponin: do think twice, it's not all right

A questionable scientific approach to measuring at low concentrations and inappropriate censoring of results below certain cut-offs have resulted in the dichotomous classification of troponin assays based on their so-called analytical sensitivity. The definition of "high-sensitivity" cardiac troponin is flawed. Evidence suggests that its apparent diagnostic superiority may be explained by the censoring of data. In the evaluation of the detection and quantification capabilities of analytical methods we recommend alignment with International Union of Pure and Applied Chemistry (IUPAC) guidelines, including reporting of all results. This will allow the objective evaluation of the diagnostic performance of troponin assays and will render the current troponin assay classification and nomenclature obsolete.

Variability and Error in Cardiac Troponin Testing: An ACLPS Critical Review

OBJECTIVES

To provide a comprehensive overview of the complexities associated with cardiac troponin (cTn) testing. An emphasis is placed on the sources of error, organized into the preanalytical, analytical, and postanalytical phases of the testing pathway. Controversial areas are also explored.

METHODS

A case scenario and review of the relevant literature describing laboratory considerations involving cTn testing are described.

RESULTS

Advanced comprehension of the specific assay used in a given laboratory is necessary for optimal reporting, utilization, and quality monitoring of cTn.

CONCLUSIONS

cTn assays are reliable diagnostic tests for acute myocardial infarction, but understanding their limitations is required for appropriate result interpretation.

B-type natriuretic peptide predicts an ischemic etiology of acute heart failure in patients with stage 4-5 chronic kidney disease

OBJECTIVES

The non-invasive differentiation of ischemic and non-ischemic acute heart failure (AHF) not resulting from acute myocardial infarction is difficult and has therapeutic and prognostic implications. The aim of this study was to assess whether plasma B-type natriuretic peptide (BNP) can identify ischemic etiology in patients with stage 4-5 chronic kidney disease (CKD) presenting with AHF.

DESIGN AND METHODS

We prospectively analyzed 61 patients. The diagnosis of ischemic AHF was confirmed by coronary angiography or stress myocardial perfusion imaging. Plasma levels of BNP were measured at admission (BNP1) and 48 h after admission (BNP2).

RESULTS

The mean age of the study patients was 67 years. In these patients, 70.5% had diabetes and 47.5% had dialysis-dependent CKD; 28 of these patients (45.9%) had an ischemic etiology with significantly higher concentrations of BNP1 and BNP2 than did patients without ischemia. The area under the receiver operating characteristic curve was 0.755 (P=0.001) for BNP1 and 0.868 (P<0.001) for BNP2 to detect ischemic etiology of AHF. Plasma BNP1 >2907 ng/L (odds ratio [OR], 10.9; 95% confidence interval [CI] 2.5-48.4; P=0.002) and BNP2 >2322 ng/L (OR 93.1, 95% CI 7.0-1238.7; P=0.001) were independently associated with an ischemic etiology of AHF.

CONCLUSIONS

Plasma BNP may represent a clinically useful non-invasive tool for identification of ischemic etiology of AHF in patients with stage 4-5 CKD.