Health Outcomes Categorized by Current and Previous Definitions of Acute Myocardial Infarction in an Unselected Cohort of Troponin-Naïve Emergency Department Patients

Analytical validation of cardiac troponin I assays in horses

Human cardiac troponin I (cTnI) assays have been used in equine medicine, often without prior analytical validation for equine use. In the absence of appropriate validation, the clinical significance of assay results is uncertain and can lead to misdiagnosis. We followed the American Society for Veterinary Clinical Pathology guidelines and investigated linearity, precision, limit of quantification (LoQ), and comparative recovery for 6 commercial cTnI assays developed for use in human medicine. Clinically acceptable linearity was observed in assays A-D, whereas assay E did not detect equine cTnI in any sample. Comparative recovery revealed 1-3-fold differences between assay results, and low analyte recoveries (2.2-3.4%) were observed in assay F. Precision was investigated in assays A and B, and found to be within acceptable limits. The LoQ was 1.53 ng/L for assay A, and 0.031 µg/L for assay B. Assays A and B performed within clinically acceptable limits and were deemed suitable for use in equine medicine. Assays C and D did not undergo full validation but had acceptable linearity, which demonstrates their potential for use in equine medicine. Assays E and F are unsuitable for use in horses given issues with detection of equine cTnI. The variability in results between assays indicates that reference intervals and cutoffs for diagnostic decision-making are assay specific and should be established prior to adoption by diagnostic laboratories.

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.

Effectiveness of practices for improving the diagnostic accuracy of Non ST Elevation Myocardial Infarction in the Emergency Department: A Laboratory Medicine Best Practices™ systematic review

OBJECTIVES

This article is a systematic review of the effectiveness of four practices (assay selection, decision point cardiac troponin (cTn) threshold selection, serial testing, and point of care testing) for improving the diagnostic accuracy Non-ST-Segment Elevation Myocardial Infarction (NSTEMI) in the Emergency Department.

DESIGN AND METHODS

The CDC-funded Laboratory Medicine Best Practices (LMBP) Initiative systematic review method for quality improvement practices was used.

RESULTS

The current ACC/AHA guidelines recommend using cardiac troponin assays with a 99th percentile upper reference limit (URL) diagnostic threshold to diagnose NSTEMI. The evidence in this systematic review indicates that contemporary sensitive cTn assays meet the assay profile requirements (sensitivity, specificity, PPV, and NPV) to more accurately diagnose NSTEMI than alternate tests. Additional biomarkers did not increase diagnostic effectiveness of cTn assays. Sensitivity, specificity, and NPV were consistently high and low PPV improved with serial sampling. Evidence for use of point of care cTn testing was insufficient to make recommendation, though some evidence suggests that use may result in reduction to patient length of stay and costs.

CONCLUSIONS

Based on the review of and the LMBP(TM) A-6 Method criteria, we recommend the use of cardiac troponin assays without additional biomarkers using the 99th percentile URL as the clinical diagnostic threshold for the diagnosis of NSTEMI. We recommend serial sampling with one sample at presentation and at least one additional second sample taken at least 6h later to identify a rise or fall in the troponin level. No recommendation is made either for or against the use of point of care tests.

DISCLAIMER

The findings and conclusions in this article are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention/the Agency for Toxic Substances and Disease Registry (CDC/ATSDR).

Root cause analysis of delays to discharge for patients held for serial cardiac troponin levels

OBJECTIVE

Emergency department (ED) patients with symptoms of cardiac ischemia often require a second cardiac troponin (cTn) measurement to rule out non-ST elevation myocardial infarction. We measured the total turnaround time and the component event times following the ordering of the second cTn level to ED discharge to identify root causes of delays.

METHODS

We reviewed a random sample of ED discharges following a second normal cTn measurement and recorded associated event times. The central tendency of time intervals is reported as median and mean number of minutes with interquartile ranges (IQRs) and 95% confidence intervals, respectively.

RESULTS

From 9,656 eligible cases, we randomly selected 226 for data collection. The median number of minutes for each event are as follows: from ordering the second cTn measurement to the time of ED discharge was 90 minutes (IQR 65-120); for blood collection from the time the collection was ordered for was 0 minutes (IQR -12-0); from blood collection to the time the blood was transported to the laboratory was 9 minutes (IQR 2-19); laboratory process duration was 44 minutes (IQR 39-52); from when the results were available to the time the patient was discharged was 30 minutes (IQR 15-52).

CONCLUSIONS

For ED patients discharged following two normal cTn levels, the laboratory processing time and time from the result being available to the time of ED discharge represent the longest modifiable time periods to reduce ED length of stay.

High-Sensitivity Cardiac Troponin I Measurement for Risk Stratification in a Stable High-Risk Population

BACKGROUND

Past investigations regarding the utility of high-sensitivity cardiac troponin I (cTnI) assays have been focused primarily on the acute coronary syndrome setting. We assessed whether such assays can predict future ischemic cardiovascular events in a stable high-risk population.

METHODS

We quantified serum cTnI using an investigational high-sensitivity assay (hs-cTnI IUO, Beckman Coulter) in 2572 participants from the Heart Outcomes Prevention Evaluation (HOPE) study. The derived ROC curve cutoff and the 99th percentile for the hs-cTnI assay were assessed by Kaplan–Meier and Cox analyses for the primary outcome [composite of myocardial infarction (MI), stroke, and cardiovascular death] at 4.5 years of follow-up. We also assessed individual outcomes (MI, stroke, cardiovascular death) and the combined outcome (MI/cardiovascular death) by regression analyses to determine hazard ratios (HRs) and c statistics in models that included established risk factors, C-reactive protein, and N-terminal pro-B–type natriuretic peptide (NT-proBNP).

RESULTS

Participants with hs-cTnI >6 ng/L (ROC cutoff) were at higher risk for the primary outcome (HR 1.38, 95% CI 1.09–1.76; P = 0.008, adjusted models). For the individual outcomes, participants with hs-cTnI above the 99th percentile (≥10 ng/L) had higher risk for cardiovascular death (HR 2.15, 95% CI 1.32–3.52; P = 0.002) and MI (HR 1.49, 95% CI 1.05–2.10; P = 0.025) but not stroke (HR 1.38, 95% CI 0.76–2.47; P = 0.288, adjusted models). Addition of hs-cTnI to an established risk model with NT-proBNP also yielded a higher c statistic for the combined outcome of MI/cardiovascular death.

CONCLUSIONS

The investigational Beckman Coulter hs-cTnI assay provides prognostic information for future MI and cardiovascular death in a stable high-risk population.

PAPP-A as a marker of increased long-term risk in patients with chest pain

OBJECTIVES

Long-term risk stratification in patients presenting with acute coronary syndromes (ACS) is possible by measuring cardiac troponin (cTn). The present study examined whether PAPP-A measured in an emergency department (ED) chest pain population in association with conventional and novel high sensitivity cTn (hs-cTnI) assays can predict long-term mortality.

METHODS

In 320 patients with cTn measurements the earliest heparinized plasma PAPP-A concentration after presentation was used for risk stratification for death by Kaplan-Meier and Cox analyses. Subgroup analyses using the earliest PAPP-A concentrations were also performed in a cohort of subjects with presentation cTnI < or = 99th percentile but with significantly changing cardiac troponin concentrations as measured by the AccuTnI assay and the hs-cTnI assay (n=45 and 120 subjects, respectively).

RESULTS

Subjects with PAPP-A concentrations in the highest tertile were at higher risk for death (HR > 2.00; p < or = 0.05 at 2 years) even after adjusting for cTnI at presentation. In the cohort with cTnI < or = 99th percentile but with changing hs-cTnI concentrations, subjects in the top PAPP-A tertile had a higher probability for death (p=0.02).

CONCLUSION

Early measurement of PAPP-A may identify chest pain patients at higher risk for long-term death. Additional prospective ACS studies are required to fully elucidate PAPP-A's role.

Is a pattern of increasing biomarker concentrations important for long-term risk stratification in acute coronary syndrome patients presenting early after the onset of symptoms?

BACKGROUND

Guidelines for treatment of acute coronary syndrome (ACS) recommend observing a rise or fall in cardiac troponin (cTn) concentrations for assessing acute injury. It is unknown whether a rising pattern presages a more adverse long-term prognosis than elevations that do not change. The present study assessed whether a rising pattern of cardiac biomarkers was more prognostic than simple elevations.

METHODS

We measured N-terminal pro-brain natriuretic peptide (NT-proBNP) (Roche), cTnT (Roche) and cTnI (Beckman Coulter) in 212 ACS patients. These biomarkers were measured in coincident EDTA and heparin plasma samples available from at least 2 different time points, an early first specimen obtained a median of 2 hours after onset of symptoms, interquartile range (IQR) 2-4 hours, and a later second specimen obtained at 9 hours, IQR 9-9 hours. The cTn concentration in the second specimen was used to classify myocardial necrosis (cTnI >0.04 ug/L; cTnT >0.01 ug/L). Outcomes [death, myocardial infarction (MI), heart failure (HF)] were obtained >8 years after the initial presentation. For patients with myocardial necrosis and a cTn concentration ratio (second/first measured concentrations) > or =1.00, the concentration ratios and the absolute concentrations in the second specimen were used to assess prognosis after 4 years.

RESULTS

In myocardial necrosis, the relative change (cTn2/cTn1) was greater for cTnI than for cTnT (P <0.01), whereas the relative change in NT-proBNP was the same regardless of which troponin was used to classify necrosis (P = 0.71). The concentration ratio for cTnI, cTnT, and NT-proBNP was not useful for risk stratification (i.e., death/MI/HF; P > or =0.15).

CONCLUSIONS

A rise in cardiac troponin or NT-proBNP concentration in ACS patients presenting early after onset of pain is not helpful for long-term prognosis.

Risk Stratification for Heart Failure and Death in an Acute Coronary Syndrome Population Using Inflammatory Cytokines and N-Terminal Pro-Brain Natriuretic Peptide

Background: Inflammation in acute coronary syndrome (ACS) can identify those at greater long-term risks for heart failure (HF) and death. The present study assessed the performance of interleukin (IL)-6, IL-8, and monocyte chemoattractant protein-1 (MCP-1) (cytokines involved in the activation and recruitment of leukocytes) in addition to known biomarkers [e.g., N-terminal pro-brain natriuretic peptide (NT-proBNP)] for predicting HF and death in an ACS population.

Methods: In a cohort of 216 ACS patients, NT-proBNP (Elecsys®; Roche) and IL-6, IL-8, and MCP-1 (evidence investigator™; Randox) were measured in serial specimens collected early after symptom onset (n = 723). We collected at least 2 specimens from each participant: an early specimen (median 2 h; interquartile range 2–4 h) and a later specimen (9 h; 9–9 h), and used the later specimens’ biomarker concentrations for risk stratification.

Results: An increase in both IL-6 and NT-proBNP was observed but not for IL-8 or MCP-1 early after pain onset. Kaplan–Meier analysis demonstrated that individuals with increased NT-proBNP (&gt;183 ng/L) or cytokines (IL-6 &gt; 6.4 ng/L; above upper limit of normal for IL-8 or MCP-1) had a greater probability of death or HF in the following 8 years (P &lt;0.05). In a Cox proportional hazard model adjusted for both CRP and troponin I, increased IL-6, MCP-1, and NT-proBNP remained significant risk factors. Combining all 3 biomarkers resulted in a higher likelihood ratio for death or HF than models restricted to any 2 of these biomarkers.

Conclusion: IL-6, MCP-1, and NT-proBNP are independent predictors of long-term risk of death or HF, highlighting the importance of identifying leukocyte activation and recruitment in ACS patients.

The use of biomarkers for the evaluation and treatment of patients with acute coronary syndromes

The advent of inexpensive, highly accurate, and predictive markers of myocardial injury, inflammation, and hemodynamic stability has revolutionized the evaluation and treatment of patients who have acute coronary syndromes (ACSs). These blood biomarkers require small sample volumes, can be run expeditiously, and provide important information concerning the diagnosis, risk stratification, and treatment of these patients. To understand the use of these markers, one must have some knowledge about what elevations in these markers imply, how they have to be collected and measured to provide reliable information, when to suspect analytic confounds, and what the key values are that impart the diagnostic, prognostic, and therapeutic information. This article discusses these issues, emphasizing what clinicians must know for optimal test use, and then addresses the practical use of these markers in patients who have ACS.

Effects of contemporary troponin assay sensitivity on the utility of the early markers myoglobin and CKMB isoforms in evaluating patients with possible acute myocardial infarction

BACKGROUND

The 2003 American Heart Association (AHA) definition for myocardial infarction (MI) requires an "adequate set" (i.e. at least 6 h between measurements) of biomarkers and specifically troponin for the diagnosis of MI. The aim of the present study was to assess the performance of myoglobin, the CKMB isoforms, and cardiac troponin I (cTnI) in specimens earlier than the requisite 6 h after presentation, in a population originally characterized using World Health Organization (WHO) criteria.

METHODS

In 1996, 228 acute coronary syndrome patients with an "adequate sample set" had their specimens assayed for CKMB isoforms and myoglobin. In 2003, the same specimens were analyzed with the AccuTnI troponin I assay and myoglobin (Beckman Coulter Access immunoassay).

RESULTS

The clinical sensitivities for both myoglobin and the CKMB isoforms were >90% when the population was classified by WHO criteria. However the sensitivities were <70% when the ESC/ACC MI definition was used. Analyzing cTnI at earlier time points as long as there was at least 3 h between specimens or at least 1 specimen 6 h from pain onset did not misclassify subjects based on adverse outcomes in the year following their presentation.

CONCLUSION

Contemporary assays for cTnI with increased analytical sensitivity reduce the utility of myoglobin and CKMB isoforms to rule-out an AMI.

Cardiovascular biomarkers: The state of the art in 2006

BACKGROUND

The explosion in cardiovascular biomarkers has been stimulated in large part by proteomics, genomics and an improved understanding of the pathophysiology of cardiovascular disease. New advances are occurring rapidly and remaining on the cutting edge of the science is harder and harder. In the past few years, major changes have evolved in our ability to use cardiac troponin, BNP and CRP which will markedly impact on their clinical utility. These changes including greater sensitivity, a better understanding of what specific fragments are being measured and how these markers are used clinically is obligatory. There is also a need for new markers.

CONCLUSIONS

As with other disciplines, this work has built on the work of others.

Elevated C-reactive protein in acute coronary syndrome presentation is an independent predictor of long-term mortality and heart failure

OBJECTIVES

To assess the ability of C-reactive protein (CRP) to predict long-term outcomes in a chest pain population.

DESIGN AND METHODS

CRP was measured at presentation in 446 emergency department patients with acute coronary syndromes. All-cause mortality and hospital discharges for acute myocardial infarction (AMI) and congestive heart failure (CHF) were obtained for up to 8 years following the event.

RESULTS

Kaplan-Meier analyses indicated that patients with CRP concentrations above the American Heart Association scientific statement cut-off had a higher rate for death and CHF admissions. After adjusting for troponin concentrations, in a Cox proportional hazard model, only CRP concentrations indicative of an acute phase response (i.e., >7.44 mg/L) were associated with a significant risk for death after 5 years and CHF readmission after 2 years.

CONCLUSIONS

Patients presenting early with chest pain with elevated CRP concentrations have a greater long-term risk for death and heart failure.

Long-Term Health Outcomes Associated with Detectable Troponin I Concentrations

Background: Recent data suggest that older men with detectable cardiac troponin I (cTnI) concentrations that remain below the 99th percentile concentration cutoff are at increased risk for subsequent cardiovascular events. We designed this study to extend this observation by examining risk prediction in both men and women presenting to an emergency department with chest discomfort.

Methods: We obtained data for all-cause mortality and hospital discharges associated with either acute myocardial infarction (AMI) or congestive heart failure (CHF) for up to 8 years after the initial presentation in 448 patients who originally presented in 1996 with acute coronary syndrome (ACS). We performed retrospective analysis for cTnI (AccuTnI™; Beckman Coulter) in frozen plasma samples based on the patients’ reported time from onset of symptoms. Peak cTnI concentration was used for risk assessment.

Results: Patients with cTnI concentrations ≥0.02 μg/L (i.e., limit of detection), including those whose peak values remained below the 99th percentile (0.04 μg/L), were at greater risk for death and AMI/CHF readmissions at 2, 5, and 8 years of follow-up compared with those with peak cTnI &lt;0.02 μg/L. All results were statistically significant (P &lt;0.05) except for death within 2 years among patients with normal but detectable cTnI (0.02 to 0.03 μg/L), relative to the group with values &lt;0.02 μg/L. Kaplan–Meier analyses indicated that both men and women with cTnI ≥0.02 μg/L had worse outcomes (P &lt;0.001).

Conclusion: Both men and women who present with possible ACS with detectable cTnI concentrations that remain below the 99th percentile are at a greater risk for future adverse events.