Determination of Clinically Acceptable Analytical Variation of Cardiac Troponin at Decision Thresholds.

BACKGROUND: Clinical decision-making for risk stratification for possible myocardial infarction (MI) uses high-sensitivity cardiac troponin (hs-cTn) thresholds that range from the limit of detection to several-fold higher than the upper reference limit (URL). To establish a minimum analytical variation standard, we can quantify the effect of variation on the population clinical measures of safety (sensitivity) and effectiveness [proportion below threshold, or positive predictive value (PPV)]. METHODS: From large datasets of patients investigated for possible MI with the Abbott hs-cTnI and Roche hs-cTnT assays, we synthesized datasets of 1 000 000 simulated patients. Troponin concentrations were randomly varied several times based on absolute deviations of 0.5 to 3 ng/L and relative changes of 2% to 20% around the low-risk threshold (5 ng/L) and URLs, respectively. RESULTS: For both assays at the low-risk thresholds, there were negligible differences in sensitivity (<0.3%) with increasing analytical variation. The proportion of patients characterized as low risk reduced by 30% to 29% (Roche) and 53% to 44% (Abbott). At the URL, increasing analytical variation also did not change sensitivity; the PPV fell by less than 3%. For risk stratification, increased delta thresholds (change between serial troponin concentrations) increased sensitivity at the cost of a decreased percentage of patients below the delta threshold, with the largest changes at the greatest analytical variation. CONCLUSIONS: At the low-risk threshold, analytical variation up to 3 ng/L minimally impacted the safety metric (sensitivity) but marginally reduced effectiveness. Similarly, at the URL even relative variation up to 25% minimally impacted safety metrics and effectiveness. Analytical variation for delta thresholds did not negatively impact sensitivity but decreased effectiveness.

Prognostic performance of soluble urokinase plasminogen activator receptor for heart failure or mortality in Western and Asian patients with acute breathlessness.

AIMS: The performance of circulating soluble urokinase plasminogen activator receptor (suPAR) for predicting the composite endpoint of subsequent heart failure (HF) hospitalisation and/or death at 1 year was assessed in (i) patients with undifferentiated breathlessness, and generalisability was compared in (ii) disparate Western versus Asian sub-cohorts, and in (iii) the sub-cohort adjudicated with HF. METHODS AND RESULTS: Patients with acute breathlessness were recruited from the emergency departments in New Zealand (NZ, n = 612) and Singapore (n = 483). suPAR measured in the presentation samples was higher in patients incurring the endpoint (n = 281) compared with survivors (5.2 ng/mL vs 3.1 ng/mL, P < 0.0001). The discriminative power of suPAR for endpoint prediction was c-statistic of 0.77 in the combined population, but was superior in Singapore than NZ (c-statistic: 0.83 vs 0.71, P < 0.0001). Although the highest suPAR tertile (>4.37 ng/mL) was associated with risks of >4-fold in NZ, >20-fold in Singapore, and ≥3-fold in HF for incurring the outcome, there was no interaction between country and suPAR levels after adjustment. Multivariable analysis indicated suPAR to be robust in predicting HF/death at 1-year [hazard ratio: 1.9 (95% CI:1.7 to 2.0) per SD increase] and improved risk discrimination for outcome prediction in HF (∆0.06) and for those with NT-proBNP >1000 pg/mL (∆0.02). CONCLUSION: suPAR is a strong independent predictor of HF and/or death at 1 year in acutely breathless patients, in both Asian and Western cohorts, and in HF. suPAR may improve stratification of acutely breathless patients, and in acute HF, for risk of later onset of heart failure or mortality.

Derivation and Validation of Thresholds Using Synthetic Data Methods for Single-Test Screening of Emergency Department Patients with Possible Acute Myocardial Infarction Using a Point-of-Care Troponin Assay.

BACKGROUND: Single-sample (screening) rule-out of acute myocardial infarction (AMI) with troponin requires derivation of a single-test screening threshold. In data sets with small event numbers, the lowest one or two concentrations of myocardial infarction (MI) patients dictate the threshold. This is not optimal. We aimed to demonstrate a process incorporating both real and synthetic data for deriving such thresholds using a novel pre-production high-precision point-of-care assay. METHODS: cTnI concentrations were measured from thawed plasma using the Troponin I Next (TnI-Nx) assay (i-STAT; Abbott) in adults on arrival to the emergency department with symptoms suggestive of AMI. The primary outcome was an AMI or cardiac death within 30 days. We used internal-external validation with synthetic data production based on clinical and demographic data, plus the measured TnI-Nx concentration, to derive and validate decision thresholds for TnI-Nx. The target low-risk threshold was a sensitivity of 99% and a high-risk threshold specificity of >95%. RESULTS: In total, 1356 patients were included, of whom 191 (14.1%) had the primary outcome. A total of 500 synthetic data sets were constructed. The mean low-risk threshold was determined to be 5 ng/L. This categorized 38% (95% CI, 6%-68%) to low-risk with a sensitivity of 99.0% (95% CI, 98.6%-99.5%) and a negative predictive value of 99.4% (95% CI, 97.6%-99.8%). A similarly derived high-risk threshold of 25 ng/L had a specificity of 95.0% (95% CI, 94.8%-95.1%) and a positive predictive value of 74.8% (95% CI, 71.5%-78.0%). CONCLUSIONS: With the TnI-Nx assay, we successfully demonstrated an approach using synthetic data generation to derive low-risk thresholds for safe and effective screening.

Cardiac effects of myoregulin in ischemia-reperfusion.

Myoregulin is a recently discovered micropeptide that controls calcium levels by inhibiting the intracellular calcium pump sarco-endoplasmic reticulum Ca2+-ATPase (SERCA). Keeping calcium levels balanced in the heart is essential for normal heart functioning, thus myoregulin has the potential to be a crucial regulator of cardiac muscle performance by reducing the rate of intracellular Ca2+ uptake. We provide the first report of myoregulin mRNA expression in human heart tissue, absence of expression in human plasma, and the effects of myoregulin on cardiac hemodynamics in an ex vivo Langendorff isolated rat heart model of ischemia/reperfusion. In this preliminary study, myoregulin provided a cardio-protective effect, as assessed by preservation of left ventricular contractility and relaxation, during ischemia/reperfusion. This study provides the foundation for future research in this area.

Personalized diagnosis in suspected myocardial infarction.

BACKGROUND: In suspected myocardial infarction (MI), guidelines recommend using high-sensitivity cardiac troponin (hs-cTn)-based approaches. These require fixed assay-specific thresholds and timepoints, without directly integrating clinical information. Using machine-learning techniques including hs-cTn and clinical routine variables, we aimed to build a digital tool to directly estimate the individual probability of MI, allowing for numerous hs-cTn assays. METHODS: In 2,575 patients presenting to the emergency department with suspected MI, two ensembles of machine-learning models using single or serial concentrations of six different hs-cTn assays were derived to estimate the individual MI probability (ARTEMIS model). Discriminative performance of the models was assessed using area under the receiver operating characteristic curve (AUC) and logLoss. Model performance was validated in an external cohort with 1688 patients and tested for global generalizability in 13 international cohorts with 23,411 patients. RESULTS: Eleven routinely available variables including age, sex, cardiovascular risk factors, electrocardiography, and hs-cTn were included in the ARTEMIS models. In the validation and generalization cohorts, excellent discriminative performance was confirmed, superior to hs-cTn only. For the serial hs-cTn measurement model, AUC ranged from 0.92 to 0.98. Good calibration was observed. Using a single hs-cTn measurement, the ARTEMIS model allowed direct rule-out of MI with very high and similar safety but up to tripled efficiency compared to the guideline-recommended strategy. CONCLUSION: We developed and validated diagnostic models to accurately estimate the individual probability of MI, which allow for variable hs-cTn use and flexible timing of resampling. Their digital application may provide rapid, safe and efficient personalized patient care. TRIAL REGISTRATION NUMBERS: Data of following cohorts were used for this project: BACC ( www. CLINICALTRIALS: gov ; NCT02355457), stenoCardia ( www. CLINICALTRIALS: gov ; NCT03227159), ADAPT-BSN ( www.australianclinicaltrials.gov.au ; ACTRN12611001069943), IMPACT ( www.australianclinicaltrials.gov.au , ACTRN12611000206921), ADAPT-RCT ( www.anzctr.org.au ; ANZCTR12610000766011), EDACS-RCT ( www.anzctr.org.au ; ANZCTR12613000745741); DROP-ACS ( https://www.umin.ac.jp , UMIN000030668); High-STEACS ( www. CLINICALTRIALS: gov ; NCT01852123), LUND ( www. CLINICALTRIALS: gov ; NCT05484544), RAPID-CPU ( www. CLINICALTRIALS: gov ; NCT03111862), ROMI ( www. CLINICALTRIALS: gov ; NCT01994577), SAMIE ( https://anzctr.org.au ; ACTRN12621000053820), SEIGE and SAFETY ( www. CLINICALTRIALS: gov ; NCT04772157), STOP-CP ( www. CLINICALTRIALS: gov ; NCT02984436), UTROPIA ( www. CLINICALTRIALS: gov ; NCT02060760).

Circulating erythroferrone has diagnostic utility for acute decompensated heart failure in patients presenting with acute or worsening dyspnea.

Objectives: In dyspneic patients with atrial fibrillation (AF) or obesity, the diagnostic performance of NT-proBNP for acute heart failure is reduced. We evaluated the erythroblast derived protein erythroferrone (ERFE) as an ancillary biomarker for the diagnosis of acute decompensated heart failure (ADHF) in these comorbid subgroups in both Western and Asian populations. Methods: The diagnostic performance of ERFE (Intrinsic Lifesciences) and NT-proBNP (Roche Cobas e411) for ADHF was assessed in 479 New Zealand (NZ) and 475 Singapore (SG) patients presenting with breathlessness. Results: Plasma ERFE was higher in ADHF, compared with breathlessness from other causes, in both countries (NZ; 4.9 vs. 1.4 ng/ml, p < 0.001) and (SG; 4.2 vs. 0.4 ng/ml, p = 0.021). The receiver operating characteristic (ROC) areas under the curve (AUCs) for discrimination of ADHF were reduced in the NZ cohort compared to SG for ERFE (0.75 and 0.84, p = 0.007) and NT-proBNP (0.86 and 0.92, p = 0.004). Optimal cut-off points for ERFE yielded comparable sensitivity and positive predictive values in both cohorts, but slightly better specificity, negative predictive values and accuracy in SG compared with NZ. In patients with AF, the AUC decreased for ERFE in each cohort (NZ: 0.71, n = 105, SG: 0.61, n = 44) but increased in patients with obesity (NZ: 0.79, n = 150, SG: 0.87, n = 164). Conclusions: Circulating ERFE is higher in patients with ADHF than in other causes of new onset breathlessness with fair diagnostic utility, performing better in Asian than in Western patients. The diagnostic performance of ERFE is impaired in patients with AF but not patients with obesity.

Diagnostic and prognostic performance of the ratio between high-sensitivity cardiac troponin I and troponin T in patients with chest pain.

BACKGROUND: Elevations of high-sensitivity cardiac troponin (hs-cTn) concentrations not related to type 1 myocardial infarction are common in chest pain patients presenting to emergency departments. The discrimination of these patients from those with type 1 myocardial infarction (MI) is challenging and resource-consuming. We aimed to investigate whether the hs-cTn I/T ratio might provide diagnostic and prognostic increment in this context. METHODS: We calculated the hs-cTn I/T ratio in 888 chest pain patients having hs-cTnI (Abbott Laboratories) or hs-cTnT (Roche Diagnostics) concentrations above the respective 99th percentile at 2 hours from presentation. All patients were followed for one year regarding mortality. RESULTS: The median hs-cTn I/T ratio was 3.45 (25th, 75th percentiles 1.80-6.59) in type 1 MI patients (n = 408 ☯46.0%]), 1.18 (0.81-1.90) in type 2 MI patients (n = 56 ☯6.3%]) and 0.67 (0.39-1.12) in patients without MI. The hs-cTn I/T ratio provided good discrimination of type 1 MI from no type 1 MI (area under the receiver-operator characteristic curve 0.89 ☯95% confidence interval 0.86-0.91]), of type 1 MI from type 2 MI (area under the curve 0.81 ☯95% confidence interval 0.74-0.87]), and was associated with type 1 MI in adjusted analyses. The hs-cTn I/T ratio provided no consistent prognostic value. CONCLUSIONS: The hs-cTn I/T ratio appears to be useful for early diagnosis of type 1 MI and its discrimination from type 2 MI in chest pain patients presenting with elevated hs-cTn. Differences in hs-cTn I/T ratio values may reflect variations in hs-cTn release mechanisms in response to different types of myocardial injury.

Assays Specific for BNP1-32 and NT-proBNP Exhibit a Similar Performance to Two Widely Used Assays in the Diagnosis of Heart Failure.

BACKGROUND: Secretion of cardioprotective B-type natriuretic peptide 1-32 (BNP1-32) is increased proportionately with cardiac dysfunction, but its measurement in plasma is difficult. Therefore, less specific BNP and amino-terminal proBNP (NT-proBNP) assays that detect the precursor molecule proBNP alongside BNP or NT-proBNP metabolites were developed to reflect BNP1-32 secretion and are now mandated in the diagnosis of heart failure (HF). We compared the diagnostic performance of 2 widely used clinical assays: the Roche proBNPII assay, and Abbott BNP assay, against our recently developed in-house assays that measure either intact BNP1-32 or NT-proBNP. METHODS: EDTA plasma samples obtained from patients presenting with breathlessness (n = 195, 60 [31%] with clinically adjudicated HF) were assayed using the Roche NT-proBNP and our specific in-house BNP1-32 and NTBNP assays. A subset (n = 75) were also assessed with the Abbott BNP assay. RESULTS: Roche NT-proBNP was highly correlated with BNP1-32 and NTBNP (Spearman rho = 0.92 and 0.90, respectively, both Ps < 0.001), and all 3 assays similarly discriminated acute HF from other causes of breathlessness (ROC analysis areas under the curve 0.85-0.89). The Abbott BNP assay performed similarly to the other assays. Roche NT-proBNP and BNP1-32 assays had similar sensitivity (83% and 80%), specificity (83% and 84%), positive (70% and 71%) and negative (91% and 90%) predictive values, and accuracy (both 83%) at their optimal cutoffs of 1536 and 12 ng/L, respectively. CONCLUSIONS: Since all assays exhibited similar performance in the diagnosis of HF, currently mandated assays provide a reliable proxy for circulating concentrations of active BNP1-32 in HF diagnosis.

Plasma Clearance of B-Type Natriuretic Peptide (BNP) before and after Bariatric Surgery for Morbid Obesity.

BACKGROUND: Obese patients have lower plasma concentrations of the cardiac natriuretic peptides (NPs) than their age- and sex-matched counterparts. This may reflect lower production and/or increased peptide clearance. It is unclear whether NP bioactivity is affected by obesity. METHODS: We studied the effects of obesity on B-type natriuretic peptide (BNP) clearance and bioactivity by comparing results from standardized intravenous infusions of BNP administered 2 weeks before and 6 months after bariatric surgery in 12 consecutive patients with morbid obesity (body mass index, BMI > 35 kg/m2). Anthropometric, clinical, neurohormonal, renal, and echocardiographic variables were obtained pre- and postsurgery. Pre- vs postsurgery calculated intrainfusion peptide clearances were compared. RESULTS: BMI (44.3 ± 5.0 vs 33.9 ± 5.2 kg/m2, P < 0.001) and waist circumference (130.3 ± 11.9 vs 107.5 ± 14.7 cm, P < 0.001) decreased substantially after bariatric surgery. Calculated plasma clearance of BNP was reduced (approximately 30%) after surgery. Though not controlled for, sodium intake was presumably lower after bariatric surgery. Despite this, preinfusion endogenous plasma NP concentrations did not significantly differ between pre- and postsurgery studies. The ratio of plasma N-terminal (NT)-proBNP to 24 h urine sodium excretion was higher postsurgery (P = 0.046; with similar nonsignificant findings for BNP, atrial NP (ANP) and NT-proANP), indicating increased circulating NPs for a given sodium status. Mean plasma NP concentrations for given calculated end-systolic wall stress and cardiac filling pressures (as assessed by echocardiographic E/e') rose slightly, but not significantly postsurgery. Second messenger, hemodynamic, renal, and neurohormonal responses to BNP were not altered between studies. CONCLUSION: Obesity is associated with increased clearance, but preserved bioactivity, of BNP.

Fibrinogen and hemoglobin predict near future cardiovascular events in asymptomatic individuals.

To identify circulating proteins predictive of acute cardiovascular disease events in the general population, we performed a proteomic screen in plasma from asymptomatic individuals. A "Discovery cohort" of 25 individuals who subsequently incurred a cardiovascular event within 3 years (median age = 70 years, 80% male) was matched to 25 controls remaining event-free for > 5 years (median age = 72 years, 80% male). Plasma proteins were assessed by data independent acquisition mass spectrometry (DIA-MS). Associations with cardiovascular events were tested using Cox regression, adjusted for the New Zealand Cardiovascular Risk Score. Concentrations of leading protein candidates were subsequently measured with ELISAs in a larger (n = 151) independent subset. In the Discovery cohort, 76 plasma proteins were robustly quantified by DIA-MS, with 8 independently associated with cardiovascular events. These included (HR = hazard ratio [95% confidence interval] above vs below median): fibrinogen alpha chain (HR = 1.84 [1.19-2.84]); alpha-2-HS-glycoprotein (also called fetuin A) (HR = 1.86 [1.19-2.93]); clusterin isoform 2 (HR = 1.59 [1.06-2.38]); fibrinogen beta chain (HR = 1.55 [1.04-2.30]); hemoglobin subunit beta (HR = 1.49 [1.04-2.15]); complement component C9 (HR = 1.62 [1.01-2.59]), fibronectin isoform 3 (HR = 0.60 [0.37-0.99]); and lipopolysaccharide-binding protein (HR = 1.58 [1.00-2.49]). The proteins for which DIA-MS and ELISA data were correlated, fibrinogen and hemoglobin, were analyzed in an Extended cohort, with broader inclusion criteria and longer time to events, in which these two proteins were not associated with incident cardiovascular events. We have identified eight candidate proteins that may independently predict cardiovascular events occurring within three years in asymptomatic, low-to-moderate risk individuals, although these appear not to predict events beyond three years.

Analytical and biological assessment of circulating human erythroferrone.

BACKGROUND: Erythroferrone (ERFE) is an erythroid hormone putatively involved in stress erythropoiesis. Its regional clearance and circulating form in humans, as well as levels in normal health and coronary disease remain unclear. METHODS: To establish a reference interval, ERFE was measured in 155 healthy volunteers using the Intrinsic LifeSciences ELISA. To identify trans-organ gradients in ERFE, regional blood sampling was undertaken in patients (n = 13) undergoing clinically indicated cardiac catheterisation. The Intrinsic ELISA was assessed for reproducibility, stability, linearity and possible cross-reactivity, interference and anticoagulant effects. Circulating forms of ERFE were evaluated by HPLC. RESULTS: In healthy individuals, the median concentration of ERFE was 0.51 ng/mL (IQR: 0.12-1.25), with men (n = 78) having higher levels than women (n = 77) (0.67 vs 0.32 ng/mL, p = 0.0001). ERFE concentrations in trans-organ sampling revealed no clear organ of clearance or production. Samples with high endogenous ERFE levels were suppressed by haemoglobin (≥2 g/L), bilirubin (≥200 µmol/L), lipaemia (>1 g/L), and freeze thawing (≥2 cycles), but this was not observed with low ERFE concentrations. Endogenous ERFE immunoreactivity was 46% higher in EDTA plasma compared with serum and lithium heparin plasma. On SE-HPLC, ERFE eluted as intact and cleaved forms. CONCLUSION: We provide a useful reference range for ERFE in EDTA plasma. We found no specific site of secretion or clearance. The Intrinsic ELISA performed adequately but is limited by interference and stability when endogenous levels are high. Circulating forms are multiple and complex.

Early kinetic profiles of troponin I and T measured by high-sensitivity assays in patients with myocardial infarction.

The early concentration kinetic profiles of cardiac troponin in patients with non-ST-elevated myocardial infarction (NSTEMI) measured by high-sensitivity cardiac troponin I (hs-cTnI) and T (hs-cTnT) assays have not been described. In intermediate-to-high-risk of NSTEMI patients we measured serial cTn concentrations on ED arrival, at 1, 2, 3, 6-12, 24 and 48-hours with hs-cTnI and hs-cTnT assays. Log-normal curves were fitted to concentrations from time from symptom onset, and the time to rule-out decision thresholds estimated (hs-cTnI: 2 ng/L and 5 ng/L; hs-cTnT: 5 ng/L). Among 164 patients there were 58 NSTEMI. The hs-cTnI to hs-cTnT ratio increased linearly over the first 6-12 h following symptom onset. The estimated times from symptom onset to the 2 ng/L and 5 ng/L thresholds for hs-cTnI were 1.8 (0.1-3.1) and 1.9 (1.1-3.5) hours, and to the 5 ng/L threshold for hs-cTnT 1.9 (1.1-3.8) hours. The estimated time to exceed 5 ng/L was ≥3 hours in 32.6% (95%CI: 20.0% to 48.1%) cases for hs-cTnI and 33.3% (19.6% to 50.0%) for hs-cTnT. cTnI concentrations increased at a much more rapid rate than cTnT concentrations in patients with NSTEMI. Concentrations of a high proportion of patients took longer than 3 hours from symptom onset to exceed the 5 ng/L rule-out decision threshold.

Cardiovascular effects of DWORF (dwarf open reading frame) peptide in normal and ischaemia/reperfused isolated rat hearts.

The novel peptide dwarf open reading frame (DWORF), highly conserved across species and expressed almost exclusively in cardiac ventricular muscle, may play a role in cardiac physiology and pathophysiology. The effect of direct administration of DWORF in the intact heart has not previously been examined. Accordingly, we investigated the cardiac effects of DWORF (1-30 nM) in normal isolated perfused rat hearts and hearts undergoing ischaemia/reperfusion (I/R) injury, and evaluated potential mechanisms of action. Exogenous DWORF at the top dose (30 nM) increased perfusion pressure (PP) in normal hearts, which indicates coronary vasoconstriction; and during post-ischaemic reperfusion, DWORF increased PP in a dose-dependent manner. In I/R hearts, DWORF at the top dose also increased left ventricular end-diastolic pressure and maximum and minimum derivatives of left ventricular pressure noted dP/dt(max) and dP/dt(min), respectively, without affecting developed pressure (DP). Co-infusion of DWORF with Diltiazem, an l-type Ca2+ channel blocker (1µM), in I/R hearts attenuated the falls in DP, dP/dt(max) and dP/dt(min) observed with Diltiazem alone. DWORF co-infusion with both Diltiazem and Y27632 (1µM) (a Rho-Kinase inhibitor) reversed the coronary vasodilator effect of the inhibitors administered alone. In conclusion, we provide the first evidence that DWORF has coronary vasoconstrictor actions in normal hearts and when administered during reperfusion in an ex-vivo model of cardiac I/R injury, and also exhibits positive cardiac inotropic activity in the latter setting. DWORF's effect on ventricular contractile function appears to be dependent on the l-type Ca2+ channel, whereas Rho-Kinase activity may be related to the coronary vasoconstrictor effects of DWORF.

Analytical, biochemical and clearance considerations of soluble urokinase plasminogen activator receptor (suPAR) in healthy individuals.

BACKGROUND: Soluble urokinase plasminogen activator receptor (suPAR) is an emerging marker of cardiovascular disease burden. Appropriate assessment of assay performance and reference interval are required to enable interpretation of results to facilitate its clinical application. METHODS: suPAR was measured using the suPARnostic® ELISA in 155 healthy volunteers. Assay performance was assessed for anticoagulant effect, recovery, interference, linearity and cross-reactivity. The identity of immunoreactive suPAR was confirmed by size-exclusion HPLC. To establish anatomical sites of release and uptake, we measured suPAR in regional samples from subjects undergoing cardiac catheterization. RESULTS: The median concentration of suPAR was 2.1 ng/mL (IQR:1.7-2.3) in health. In comparison with EDTA, suPAR measurements were affected by lithium heparin (>10% change) and increased with serum usage. suPAR reactivity also increased in the presence of haemolysis (10 g/L), but was suppressed with urokinase and lipids (4 g/L). In multiple regression analyses, suPAR associated independently with body weight, NT-proBNP and MR-proADM (P = .03) for healthy individuals. Regional plasma sampling showed lower suPAR concentrations in the coronary sinus and renal vein compared with concentrations in femoral arterial samples. Immunoreactive circulating suPAR species had Mr of 10-39 kDa. CONCLUSION: The suPARnostic® assay performs acceptably for a clinical assay but is limited in the presence of high levels of hemolysis, lipids and urokinase. We provide the first evidence for the heart and kidneys as organs of suPAR clearance in humans. Additional investigations are warranted to determine whether there is a need to compare the marker performance of differing circulating forms of suPAR.

ProBNP That Is Not Glycosylated at Threonine 71 Is Decreased with Obesity in Patients with Heart Failure.

BACKGROUND: Heart failure (HF) is a leading cause of morbidity and mortality worldwide. Plasma concentrations of B-type natriuretic peptide (BNP) or its amino terminal congener (NT-proBNP) are used for HF diagnosis and risk stratification. Because BNP concentrations are inexplicably lowered in obese patients, we investigated the relationship between proBNP glycosylation, plasma NT-proBNP, and body mass index (BMI) in HF patients. METHODS: Three assays were developed to distinguish between total proBNP (glycosylated plus nonglycosylated proBNP), proBNP not glycosylated at threonine 71 (NG-T71), and proBNP not glycosylated in the central region (NG-C). Intraassay and interassay CVs were <15%; limits of detection were <21 ng/L; and samples diluted in parallel. RESULT: Applying these assays and an NT-proBNP assay to plasma samples from 106 healthy volunteers and 238 HF patients determined that concentrations [median (interquartile range)] of proBNP, NG-T71, and NT-proBNP were greater in HF patients compared with controls [300 (44-664), 114 (18-254), and 179 (880-3459) ng/L vs 36 (18-229), 36 (18-175), and 40 (17-68) ng/L, respectively; all P < 0.012]. NG-C was undetectable in most samples. ProBNP concentrations in HF patients with BMI more or less than 30 kg/m2 were not different (P = 0.85), whereas HF patients with BMI >30 kg/m2 had lower NT-proBNP and NG-T71 concentrations (P < 0.003) and higher proBNP/NT-proBNP and proBNP/NG-T71 ratios (P = 0.001 and P = 0.02, respectively) than those with BMI <30 kg/m2. CONCLUSIONS: Increased BMI is associated with decreased concentrations of proBNP not glycosylated at T71. Decreased proBNP substrate amenable to processing could partially explain the lower NT-proBNP and BNP concentrations observed in obese individuals, including those presenting with HF.

Validity of a Novel Point-of-Care Troponin Assay for Single-Test Rule-Out of Acute Myocardial Infarction.

Importance: Emergency department (ED) investigations of patients with suspected acute myocardial infarction (AMI) are time consuming, partly because of the turnaround time of laboratory tests. Current point-of-care troponin assays shorten test turnaround times but lack precision at lower concentrations. Development of point-of-care troponin assays with greater analytical precision could reduce the decision-making time in EDs for ruling out AMI. Objective: To determine the clinical accuracy for AMI of a single troponin concentration measured on arrival to ED with a new-generation, higher precision point-of-care assay with a 15-minute turnaround time. Design, Setting, and Participants: This observational study occurred at a single urban regional ED. Adults presenting acutely from the community to the ED with symptoms suggestive of AMI were included. Troponin concentrations were measured on ED arrival with both a novel point-of-care assay (i-STAT TnI-Nx; Abbott Point of Care) and a high-sensitivity troponin I assay (Architect hs-cTnI; Abbott Diagnostics). Main Outcomes and Measures: The primary outcome was type 1 AMI during index presentation. We compared the discrimination ability of the TnI-Nx assay with the hs-cTnI assay using the area under receiver operator characteristic curve (AUC) and sensitivity, negative predictive value, and the proportion of negative test results at thresholds with 100% sensitivity. Results: Of 354 patients (255 [72.0%] men; mean [SD] age, 62 [12] years), 57 (16.1%) experienced an AMI. Eighty-five patients (24.0%) presented to the ED less than 3 hours after symptom onset. No difference was found between the AUC of the TnI-Nx assay (0.975 [95% CI, 0.958-0.993]) and the hs-cTnI assay (0.970 [95% CI, 0.949 to 0.990]; P = .46). A TnI-Nx assay result of less than 11 ng/L identified 201 patients (56.7%) as low risk, with a sensitivity of 100% (95% CI, 93.7%-100%) and a negative predictive value of 100% (95% CI, 98.2%-100%). In comparison, an hs-cTnI assay result of less than 3 ng/L identified 154 patients (43.5%) as low risk, with a sensitivity of 100% (95% CI, 93.7%-100%) and a negative predictive value of 100% (95% CI, 97.6%-100%). Conclusions and Relevance: A novel point-of-care troponin assay that can produce a result 15 minutes after blood sampling had comparable discrimination ability to an hs-cTnI assay for ruling out AMI after a single blood test. Use in the ED may facilitate earlier decision making and could expedite the safe discharge of a large proportion of low-risk patients.

Detectable High-Sensitivity Cardiac Troponin within the Population Reference Interval Conveys High 5-Year Cardiovascular Risk: An Observational Study.

BACKGROUND: Increased cardiac troponin I or T detected by high-sensitivity assays (hs-cTnI or hs-cTnT) confers an increased risk of adverse prognosis. We determined whether patients presenting with putatively normal, detectable cTn concentrations [> limit of detection and < upper reference limit (URL)] have increased risk of major adverse cardiovascular events (MACE) or all-cause mortality. METHODS: A prospective 5-year follow-up of patients recruited in the emergency department with possible acute coronary syndrome (ACS) and cTn concentrations measured with hs-cTnI (Abbott) and hs-cTnT (Roche) assays. Cox regression models were generated with adjustment for covariates in those without MACE on presentation. Hazard ratios (HRs) for hs-cTn were calculated relative to the HRs at the median concentration. RESULTS: Of 1113 patients, 836 were without presentation MACE. Of these, 138 incurred a MACE and 169 died during a median 5.8-year follow-up. HRs for MACE at the URLs were 2.3 (95% CI, 1.7-3.2) for hs-cTnI and 1.8 (95% CI, 1.3-2.4) for hs-cTnT. Corresponding HRs for mortality were 1.7 (95% CI, 1.2-2.2) for hs-cTnI and 2.3 (95 % CI, 1.7-3.1) for hs-cTnT. The HR for MACE increased with increasing hs-cTn concentration similarly for both assays, but the HR for mortality increased at approximately twice the rate for hs-cTnT than hs-cTnI. Patients with hs-cTnI ≥10 ng/L or hs-cTnT ≥16 ng/L had the same percentage of MACE at 5-year follow-up (33%) as patients with presentation MACE. CONCLUSIONS: Many patients with ACS ruled out and putatively normal but detectable hs-cTnI concentrations are at similar long-term risk as those with MACE. hs-cTnT concentrations are more strongly associated with 5-year mortality than hs-cTnI.

Accelerated diagnostic protocol using high-sensitivity cardiac troponin T in acute chest pain patients.

BACKGROUND: We aimed to evaluate the efficacy and safety of using high-sensitivity cardiac troponin T (hs-cTnT) within an accelerated diagnostic protocol (ADP) in patients presenting with symptoms suggestive of acute myocardial infarction (AMI) for rapid rule-out of AMI. METHODS: In two independent large multicenter studies, levels of hs-cTnT at presentation and at 2 h were combined with the Thrombolysis In Myocardial Infarction (TIMI) risk score and ECG findings. The ADP defined patients with normal levels of hs-cTnT at presentation and 2 h, a TIMI score ≤1, and normal ECG findings as candidates for rapid rule-out of AMI and rapid discharge. Major adverse cardiac events (MACEs) occurring within 30-days were centrally adjudicated by two independent cardiologists. RESULTS: In the derivation cohort, among 1085 consecutive patients 198 patients (18.2%) had a MACE. The ADP classified 374 patients (34.5%) as low-risk. None of these patients had a MACE at 30 days, resulting in a negative predictive value (NPV) of 100% (95% CI, 99.0-100%) and a sensitivity of 100% (95% CI, 98.2%-100%). In the validation cohort, among 1590 consecutive patients 231 patients (14.5%) had a MACE. The ADP classified 641 patients (40.3%) as low-risk. 6 of these patients had a MACE at 30 days, resulting in a NPV of 99.1% (95% CI, 98.0-99.6%) and a sensitivity of 97.4% (95% CI, 94.5-98.8%). CONCLUSIONS: The ADP including hs-cTnT allows early identification 35 to 40% of patients to be at extremely low risk of MACE and therefore ideal candidates for outpatient management.

B-type natriuretic peptide forms within the heart, coronary sinus, and peripheral circulation in humans: evidence for degradation before secretion.

BACKGROUND: The B-type natriuretic peptides (BNP and N-terminal pro-BNP) are secreted by the heart and, in the case of BNP, serve to maintain circulatory homeostasis through renal and vascular actions and oppose many effects of the renin-angiotensin system. Recent evidence suggests that in patients with severe heart failure, circulating immunoreactive BNP is made up mainly of metabolites that may have reduced bioactivity. We hypothesized that BNP may be degraded before it even leaves the heart. METHODS: Peripheral venous plasma plus atrial and ventricular tissue, obtained from explanted hearts at the time of transplantation, were collected from 3 patients with end-stage heart failure. In a separate study, plasma was collected from the coronary sinus and femoral artery of 3 separate patients undergoing cardiac catheterization. Plasma C18 reverse-phase extracts were separated on reverse-phase HPLC, and the collected fractions were subjected to RIAs with highly specific antisera directed to the amino- and carboxy-terminal ends of BNP(1-32). RESULTS: ProBNP, BNP(1-32), and 2 major BNP metabolites were present in atrial and ventricular tissue, where BNP(1-32) represented 45% and 70% of total processed BNP, respectively. Neither BNP(1-32) nor the 2 metabolites were detected in peripheral venous plasma. Nor was BNP(1-32) detected in matching coronary sinus and femoral artery plasma from the 3 patients undergoing cardiac catheterization. CONCLUSIONS: BNP(1-32) is partly degraded within the hearts of patients with end-stage heart failure, and even in patients with relatively well-preserved left ventricular systolic function, only BNP metabolites enter the systemic circulation.