Wu, Alan H.B.

Background: The observed incidence of type 2 myocardial infarction (T2MI) is expected to increase with the implementation of increasingly sensitive cTn assays. However, it remains to be determined how to diagnose, risk-stratify, and treat patients with T2MI. We aimed to discriminate and risk-stratify T2MI using biomarkers. Methods: Patients presenting to the emergency department with chest pain, enrolled in the CHOPIN study (Copeptin Helps in the early detection Of Patients with acute myocardial INfarction), were retrospectively analyzed. Two cardiologists adjudicated type 1 MI (T1MI) and T2MI. The prognostic ability of several biomarkers alone or in combination to discriminate T2MI from T1MI was investigated using receiver operating characteristic curve analysis. The biomarkers analyzed were cTnI, copeptin, MR-proANP (midregional proatrial natriuretic peptide), CT-proET1 (C-terminal proendothelin-1), MR-proADM (midregional proadrenomedullin), and procalcitonin. The prognostic utility of these biomarkers for all-cause mortality and major adverse cardiovascular event (a composite of acute myocardial infarction, unstable angina pectoris, reinfarction, heart failure, and stroke) at 180-day follow-up was also investigated. Results: Among the 2071 patients, T1MI and T2MI were adjudicated in 94 and 176 patients, respectively. Patients with T1MI had higher levels of baseline cTnI, whereas those with T2MI had higher baseline levels of MR-proANP, CT-proET1, MR-proADM, and procalcitonin. The area under the receiver operating characteristic curve for the diagnosis of T2MI was higher for CT-proET1, MR-proADM, and MR-proANP (0.765, 0.750, and 0.733, respectively) than for cTnI (0.631). Combining all biomarkers resulted in a similar accuracy to a model using clinical variables and cTnI (0.854 versus 0.884, P =0.294). Addition of biomarkers to the clinical model yielded the highest area under the receiver operating characteristic curve (0.917). Other biomarkers, but not cTnI, were associated with mortality and major adverse cardiovascular event at 180 days among all patients, with no interaction between the diagnosis of T1MI or T2MI. Conclusions: Assessment of biomarkers reflecting pathophysiologic processes occurring with T2MI might help differentiate it from T1MI. All biomarkers measured, except cTnI, were significant predictors of prognosis, regardless of the type of myocardial infarction.

Abstract Background Concerns exist regarding how the 99th percentile upper reference limit (URL) of cardiac troponin (cTn) is determined and whether it should be derived from normal healthy individuals. Content The 99th percentile URL of cTn is an important criterion to standardize the diagnosis of myocardial infarction (MI) for clinical, research, and regulatory purposes. Statistical heterogeneity in its calculation exists but recommendations have been proposed. Some negativity has resulted from the fact that with some high-sensitivity (hs) cTn assays, a greater number of increases above the 99th percentile are observed when transitioning from a contemporary assay. Increases reflect acute or chronic myocardial injury and provide valuable diagnostic and prognostic information. The etiology of increases can sometimes be difficult to determine, making a specific treatment approach challenging. For those reasons, some advocate higher cutoff concentrations. This approach can contribute to missed diagnoses. Contrary to claims, neither clinical or laboratory guidelines have shifted away from the 99th percentile. To support the diagnosis of acute MI, the 99th percentile URL remains the best-established approach given the absence of cTn assay standardization. Importantly, risk stratification algorithms using hs-cTn assays predict the possibility of MI diagnoses established using the 99th percentile. Summary The 99th percentile of cTn remains the best-established criterion for the diagnosis of acute MI. While not perfect, it is analytically and clinically evidence-based. Until there are robust data to suggest some other approach, staying with the 99th percentile, a threshold that has served the field well for the past 20 years, appears prudent.

Abstract Background How to select healthy reference subjects in deriving 99th percentiles for cardiac troponin assays still needs to be clarified. To assist with global implementation of high sensitivity (hs)-cardiac troponin (cTn) I and hs-cTnT assays in clinical practice, we determined overall and sex-specific 99th percentiles in 9 hs-cTnI and 3 hs-cTnT assays using a universal sample bank (USB). Methods The Universal Sample Bank (USB) comprised healthy subjects, 426 men and 417 women, screened using a health questionnaire. Hemoglobin A1c (>URL 6.5%), NT-proBNP (>URL 125 ng/L) and eGFR (<60 mL/min), were used as surrogate biomarker exclusion criteria along with statin use. 99th percentiles were determined by nonparametric, Harrell--Davis bootstrap, and robust methods. Results Subjects were ages 19 to 91 years, Caucasian 58%, African American 27%, Pacific Islander/Asian 11%, other 4%, Hispanic 8%, and non-Hispanic 92%. The overall and sex-specific 99th percentiles for all assays, before and after exclusions (n = 694), were influenced by the statistical method used, with substantial differences noted between and within both hs-cTnI and hs-cTnT assays. Men had higher 99th percentiles (ng/L) than women. The Roche cTnT and Beckman and Abbott cTnI assays (after exclusions) did not measure cTn values at ≥ the limit of detection in ≥50% women. Conclusions Our findings have important clinical implications in that sex-specific 99th percentiles varied according to the statistical method and hs-cTn assay used, not all assays provided a high enough percentage of measurable concentrations in women to qualify as a hs-assay, and the surrogate exclusion criteria used to define normality tended to lower the 99th percentiles.

Abstract Background The assessment of kidney function and detection of acute kidney injury (AKI) remain cumbersome. On the one hand, because of limited accuracy of established tests: The most widely used methods are creatinine based, which lack in sensitivity, as creatinine is not purely filtrated by the kidney and rises relatively late after onset of AKI. On the other hand, because of labor-intensiveness: Gold standard inulin clearance and comparable methods involve intravenous compound infusion, blood sampling at several time points, and have error-sensitive determination methods. In recent years, several biomarkers have been put forward (e.g., NGAL, KIM-1, TIMP-2*IGFBP-7), but clinical implementation is limited up to now. Content Proenkephalin (PENK) represents a new candidate to determine kidney function. This peptide is cleaved from the precursor peptide preproenkephalin A alongside enkephalins (endogenous opioids) and is filtrated in the glomerulus. PENK plasma concentration appears to accurately represent glomerular filtration rate in patients diagnosed with sepsis or cardiac diseases. Moreover, increased PENK concentration is found to be associated with longer-term outcome concerning AKI and cardiac diseases. Lastly, the predominant receptor of enkephalins, the δ-opioid receptor, is expressed with the highest density in the kidney, suggesting that enkephalins could also exert a direct effect on kidney function. Summary In this review, we present an overview of enkephalins and the assessment of kidney function using this possible new functional biomarker PENK and compare it with established and novel biomarkers.

Background: Copeptin in combination with troponin has been shown to have incremental value for the early rule-out of myocardial infarction, but its performance in Black patients specifically has never been examined. In light of a potential for wider use, data on copeptin in different relevant cohorts are needed. This is the first study to determine whether copeptin is equally effective at ruling out myocardial infarction in Black and Caucasian races. Methods: This analysis of the CHOPIN trial included 792 Black and 1075 Caucasian patients who presented to the emergency department with chest pain and had troponin-I and copeptin levels drawn. Results: One hundred and forty-nine patients were diagnosed with myocardial infarction (54 Black and 95 Caucasian). The negative predictive value of copeptin at a cut-off of 14 pmol/l (as in the CHOPIN study) for myocardial infarction was higher in Blacks (98.0%, 95% confidence interval (CI) 96.2–99.1%) than Caucasians (94.1%, 95% CI 92.1–95.7%). The sensitivity at 14 pmol/l was higher in Blacks (83.3%, 95% CI 70.7–92.1%) than Caucasians (53.7%, 95% CI 43.2–64.0%). After controlling for age, hypertension, heart failure, chronic kidney disease and body mass index in a logistic regression model, the interaction term had a P value of 0.03. A cut-off of 6 pmol/l showed similar sensitivity in Caucasians as 14 pmol/l in Blacks. Conclusions: This is the first study to identify a difference in the performance of copeptin to rule out myocardial infarction between Blacks and Caucasians, with increased negative predictive value and sensitivity in the Black population at a cut-off of 14 pmol/l. This also holds true for non-ST-segment elevation myocardial infarction and, although numbers were small, similar trends exist in the normal troponin population. This may have significant implications for early rule-out strategies using copeptin.

Abstract This document is an essential companion to the third iteration of the National Academy of Clinical Biochemistry [NACB,8 now the American Association for Clinical Chemistry (AACC) Academy] Laboratory Medicine Practice Guidelines (LMPG) on cardiac markers. The expert consensus recommendations were drafted in collaboration with the International Federation of Clinical Chemistry and Laboratory Medicine Task Force on Clinical Applications of Bio-Markers (IFCC TF-CB). We determined that there is sufficient clinical guidance on the use of cardiac troponin (cTn) testing from clinical practice groups. Thus, in this expert consensus document, we focused on clinical laboratory practice recommendations for high-sensitivity (hs)-cTn assays. This document utilized the expert opinion class of evidence to focus on the following 10 topics: (a) quality control (QC) utilization, (b) validation of the lower reportable analytical limits, (c) units to be used in reporting measurable concentrations for patients and QC materials, (d) 99th percentile sex-specific upper reference limits to define the reference interval; (e) criteria required to define hs-cTn assays, (f) communication with clinicians and the laboratory's role in educating clinicians regarding the influence of preanalytic and analytic problems that can confound assay results, (g) studies on hs-cTn assays and how authors need to document preanalytical and analytical variables, (h) harmonizing and standardizing assay results and the role of commutable materials, (i) time to reporting of results from sample receipt and sample collection, and (j) changes in hs-cTn concentrations over time and the role of both analytical and biological variabilities in interpreting results of serial blood collections.

Abstract Aims Biomarkers can be used for diagnosis, risk stratification, or management of patients with heart failure (HF). Knowledge about the biological variation is needed for proper interpretation of serial measurements. Therefore, we aimed to determine and compare the biological variation of a large panel of biomarkers in healthy subjects and in patients with chronic HF. Methods and results The biological variability of established biomarkers [NT-proBNP and high-sensitivity troponin T (hsTnT)], novel biomarkers [galectin-3, suppression of tumorigenicity 2 (ST2), and growth differentiation factor 15 (GDF-15)], and renal/neurohormonal biomarkers (aldosterone, phosphate, parathyroid hormone, plasma renin concentration, and creatinine) was determined in 28 healthy subjects and 83 HF patients, over a period of 4 months and 6 weeks, respectively. The analytical (CVa), intraindividual (CVi), and interindividual (CVg) variations were calculated, as well as the reference change value (RCV), which reflects the percentage of change that may indicate a ‘relevant’ change. All crude biomarker levels were significantly increased or decreased in HF patients compared with controls (all P < 0.01). Variation indices were comparable in healthy individuals and HF patients. CVi was not influenced by the individual levels of the biomarker itself. NT-proBNP and GDF-15 had relatively high CVi (21.8% and 16.6%) and RCV (61.7% and 64.3%), whereas ST2 (CVi, 15.0; RCV, 42.9%), hsTnT (CVi, 11.1; RCV, 31.4%), and galectin-3 (CVi, 8.1; RCV, 25.0%) had lower indices of variation. Conclusion Biological variation indices are comparable between healthy subjects and HF patients for a broad spectrum of biomarkers. NT-proBNP and GDF-15 have substantial variation, with lower variation for ST2, hsTnT, and galectin-3. These data are instrumental in proper interpretation of biomarker levels in HF patients.