Diagnosis of type 1 and type 2 myocardial infarction using a high-sensitivity cardiac troponin I assay with sex-specific 99th percentiles based on the third universal definition of myocardial infarction classification system.

BACKGROUND: The frequency and characteristics of myocardial infarction (MI) subtypes per the Third Universal Definition of MI (TUDMI) classification system using high-sensitivity (hs) cardiac troponin assays with sex-specific cutoffs is not well known. We sought to describe the diagnostic characteristics of type 1 (T1MI) and type 2 (T2MI) MI using an hs-cardiac troponin I (hs-cTnI) assay with sex-specific cutoffs. METHODS: A total of 310 consecutive patients with serial cTnI measurements obtained on clinical indication were studied with contemporary and hs-cTnI assays. Ninety-ninth percentile sex-specific upper reference limits (URLs) for the hs-cTnI assay were 16 ng/L for females and 34 ng/L for males. The TUDMI consensus recommendations were used to define and adjudicate MI based on each URL. RESULTS: A total of 127 (41%) patients had at least 1 hs-cTnI exceeding the sex-specific 99th percentiles, whereas 183 (59%) had hs-cTnI within the reference interval. Females had more myocardial injury related to supply/demand ischemia than males (39% vs 18%, P = 0.01), whereas males had more multifactorial or indeterminate injury (52% vs 33%, P = 0.05). By hs-cTnI, there were 32 (10%) acute MIs, among which 10 (3%) were T1MI and 22 (7%) were T2MI. T2MI represented 69% (22 out of 32) of all acute MIs, whereas T1MI represented 31% (10 out of 32). Ninety-five patients (31%) had an increased hs-cTnI above the 99th percentile but did not meet criteria for acute MI. The most common triggers for T2MI were tachyarrhythmias, hypotension/shock, and hypertension. By contemporary cTnI, more MIs (14 T1MI and 29 T2MI) were diagnosed. By contemporary cTnI, there were 43 MIs, 14 T1MI, and 29 T2MI. CONCLUSIONS: Fewer MI diagnoses were found with the hs-cTnI assay, contrary to the commonly accepted idea that hs-cTnI will lead to excessive false-positive diagnoses.

Electronic medical record-based performance improvement project to document and reduce excessive cardiac troponin testing.

BACKGROUND: We assessed the utilization rationale behind provider ordering of cardiac troponin I (cTnI) testing for the diagnosis of myocardial infarction after implementation of a hospital-wide serial order protocol. METHODS: During 2 months in 2013, any request for additional cTnI testing within 30 days of the initial serial cTnI order prompted an electronic health record best practice alert (BPA), which included clinical decision support that could be bypassed by giving a clinical indication. cTnI orders were not limited (timing, number), and upon BPA, trigger data was collected for clinical indications and actions, patient stay (duration, location), International Classification of Diseases, Revision 9 diagnosis, cTnI orders, and timing of cTnI measurements. RESULTS: The BPA was triggered 1477 times by 423 providers who cared for 702 patients. There were a mean of 3.6 cTnI results per patient, 2.1 BPAs per patient, and 1.2 visits per patient. Providers (42% of whom were residents) acknowledged and overrode the BPA 97% of the time. In response to the BPA, 65% of providers selected a prepared rationale: 64% acute coronary syndrome/ST-elevation myocardial infarction/non-ST-elevation myocardial infarction; 30% demand ischemia; and 6% non-ACS myocardial necrosis. Of the remaining 35% of providers, 71% listed no rationale for their additional cTnI orders. Of patients with a BPA, 93% had non-ACS-related primary International Classification of Diseases, Revision 9 diagnosis, and 58% of the time, patients' cTnI results never increased during their stay. In 53% of cases, BPAs were generated by a request for an additional cTnI series when <2 results were available. CONCLUSIONS: Providers largely ignored the BPA that warned of potential overutilization of cTnI testing independent of diagnosis, including ACS.

Cardiac troponin changes to distinguish type 1 and type 2 myocardial infarction and 180-day mortality risk.

AIMS: To determine the ability of serial cardiac troponin (cTnI) changes (delta) to distinguish type 1 and type 2 myocardial infarction (MI) (excluding all ST-segment elevation MIs (STEMIs)) and describe the diagnostic accuracy and 180-day mortality in MI versus no-MI patients. METHODS AND RESULTS: Serial cTnIs were measured in 1112 consecutive patients without STEMI and within 6h of presentation to a United States emergency department: 856 (77%) with no MI, 66 (6%) type 1 MI, and 190 (17%) type 2 MI. Of the 0 to 3h and 0 to 6h absolute and relative cTnI changes, only the distribution of absolute change from 0 to 6h was significantly different between type 1 and type 2 MI: median (interquartile range) 311 (1430) ng/l vs. 80 (330) ng/l, p=0.03. Neither the absolute concentration change nor the absolute percent change from either 0 h to 3h (areas under the curves (AUCs) 0.57 and 0.54 respectively) or 0 h to 6h (AUCs 0.60 and 0.51) improved on the performance of the individual cTnI results at 3h (AUC 0.60) or 6h (AUC 0.62), respectively. After adjusting for age, and histories of heart failure and renal insufficiency, those with type 2 MI (hazard ratio 2.9, 95% confidence interval (CI) 1.4-5.9, p=0.004) and those with no index MI and cTnI(max0-6h) > 34 ng/l (2.5, CI 1.1-6.0, p=0.04) had increased risk of death within 180 days compared with those with no MI and cTnI(max 0-6h) ≤ 34 ng/l. CONCLUSION: Delta cTnI did not aid in distinguishing type 1 MI from the more common type 2 MI. Patients diagnosed with type 2 MIs, which represented more than half of all index MIs, had increased risk of death after discharge.

Diagnostic performance of four point of care cardiac troponin I assays to rule in and rule out acute myocardial infarction.

OBJECTIVE: This study evaluated the diagnostic performance of four point-of-care (POC) cardiac troponin I (cTnI) assays compared to a central laboratory cTnI assay for detecting myocardial injury and diagnosing acute myocardial infarction (AMI). DESIGN AND METHODS: Plasma obtained at admission, 3 h, and 6 h post-admission in 169 patients presenting with symptoms suggestive of acute coronary syndrome (ACS) was studied. cTnI concentrations were measured on the Instrumentation Laboratory prototype GEM Immuno, Radiometer AQT90, Mitsubishi PATHFAST, Abbott i-STAT and the Ortho-Clinical Diagnostic Vitros assays. MI was determined based on 99th percentiles according to Universal MI guidelines. RESULTS: For ruling in MI at presentation (0 h), the GEM Immuno (sensitivity 63%, specificity 85%) and PATHFAST (sensitivity 53%, specificity 86%) were comparable to the OCD (sensitivity 68%, specificity 81%), and significantly better (p<0.05) than the AQT90 (sensitivity 26%, specificity 93%) and i-STAT (sensitivity 32%, specificity 92%). cTnI concentrations and serial rising patterns after MI differed by each assay. Negative predictive values were >90% and ROC AUCs were >0.90 after 6h for all assays. Detection of myocardial injury in non-ischemic pathologies accounted for lower than 100% specificity for MI. CONCLUSION: cTnI is a sensitive biomarker for detection of myocardial injury. The analytical variability that exists between POC cTnI assays demonstrates substantial diagnostic differences for ruling in and ruling out MI in patients presenting with symptoms suggestive of ACS.

Performance characteristics of the ARCHITECT Galectin-3 assay.

OBJECTIVES: Galectin-3 is an emerging biomarker that is commonly increased in patients with heart failure and/or patients at risk for cardiovascular disease. We evaluated the Galectin-3 assay on the Abbott ARCHITECT i1000(SR) and ARCHITECT i2000(SR) at 2 testing sites. DESIGN AND METHODS: Imprecision (%CV), interference, limits of blank (LoB), detection (LoD), and quantitation (LoQ), linearity, method comparison to an ELISA method, comparisons between plasma and serum, and reference intervals were evaluated. Imprecision was performed based on two runs of duplicate testing conducted daily. Verification of LoB, LoD, and LoQ was performed according to Clinical and Laboratory Standards Institute guidelines. Linearity was evaluated by making 5 dilutions of a high patient EDTA plasma pool with a low patient pool. Reference intervals were established using EDTA plasma collected from self-reported healthy volunteers. A second lot of reagent was used at one site for method comparison and imprecision studies. RESULTS: Total CV's were ≤6.0%. A positive interference was observed for hemolyzed samples over 2.0 g/L hemolysate. The LoB ranged from 0.1 to 0.3 ng/mL, the LoD from 1.4 to 2.1 ng/mL and the LoQ from 3.0 to 3.3 ng/mL. Linearity studies had slopes and correlation coefficients equal to 1.0. Comparison of the i1000(SR) and i2000(SR) to the ELISA method demonstrated slopes of 1.0 to 1.2 and correlation coefficients of 0.93 to 0.97. The 97.5th percentile of the reference interval was 18.7 and 17.9 ng/mL for the i1000(SR) and i2000(SR), respectively. CONCLUSIONS: The Abbott Galectin-3 assay demonstrated acceptable analytical performance on both the ARCHITECT i1000(SR) and ARCHITECT i2000(SR).

Determination of 19 cardiac troponin I and T assay 99th percentile values from a common presumably healthy population.

BACKGROUND: Between-assay comparability of 99th percentiles for cardiac troponin concentrations has not been assessed systematically in a single population for a large number of assays. METHODS: We determined 99th percentiles for 19 cardiac troponin assays in heparin plasma samples from a population of 272 and 252 presumably healthy males and females, respectively. The assays evaluated included 1 cardiac troponin T (cTnT) assay from Roche and 18 cTnI assays from Abbott, Alere, Beckman, bioMerieux, Instrumentation Laboratory, Ortho-Clinical Diagnostics, Singulex, Siemens, and Roche. Five of these assays were categorized as high-sensitivity, 9 as sensitive-contemporary, and 5 as point-of-care (POC) assays. RESULTS: For high-sensitivity cTnI (hs-cTnI) assays 99th percentiles varied from 23 to 58 ng/L. At least 80% of individuals had measurable hs-cTnI, whereas only 25% had measurable high-sensitivity cTnT. All high-sensitivity cardic troponin assays had 99th percentiles that were 1.2-2.4-fold higher in males than females. For the 9 sensitive-contemporary cTnI assays, 99th percentiles varied from 12 to 392 ng/L, and only the Beckman assay gave measurable concentrations in a substantial portion of the population (35% vs ≤6% for the others). Seven of these 9 assays had 1.3-5.0-fold higher 99th percentiles for males than females. For 5 cTnI POC assays, 99th percentiles varied from <10 to 40 ng/L. The Instrumentation Laboratory assay gave measurable results in 27.8% of study participants vs ≤6% for the others. Correlations were generally poor among assays. CONCLUSIONS: Among cardiac troponin assays 99th percentile concentrations appear to differ. High-sensitivity assays provide measurable cardiac troponin results in a substantially greater fraction of presumably healthy individuals.

Delta changes for optimizing clinical specificity and 60-day risk of adverse events in patients presenting with symptoms suggestive of acute coronary syndrome utilizing the ADVIA Centaur TnI-Ultra assay.

OBJECTIVES: We determined diagnostic accuracy and risk stratification using delta changes for the cardiac troponin I (cTnI) Centaur Ultra assay for ruling out acute myocardial infarction (AMI) and for risk prediction of adverse events in patients with symptoms of acute coronary syndrome. DESIGN AND METHODS: cTnI was measured on admission and 6-24 h in 371 patients. Optimal deltas (percent change, absolute value of percent change, change, absolute value of change) were determined from ROC curve analysis. Risk stratification was performed for cardiac events and death within 60 days. RESULTS: AMI during hospitalization occurred in 49 patients and endpoints in 11 patients. Diagnostic accuracy by ROC curve was optimal (0.96) using the absolute value of change delta. Diagnostic specificities utilizing the 99th percentile (40 ng/L) for admission and follow-up samples were 84% and 81%, compared to: [90% percent change delta] 89.7%; [66.7% absolute value of percent change delta] 85.5%, [217 ng/L change delta] 99.0% and [55 ng/L absolute value of change delta] 93.7%. All four delta values showed substantially greater risk when the initial cTn value was normal. CONCLUSIONS: Utilizing delta cTnI values improves clinical specificity, diagnostic accuracy and risk assessment in patients presenting with symptoms of ACS.

Increased cardiac troponin I as measured by a high-sensitivity assay is associated with high odds of cardiovascular death: the Minnesota Heart Survey.

BACKGROUND: We examined several novel biomarkers of different pathophysiologic pathways as predictors of cardiovascular mortality in participants enrolled in the Minnesota Heart Survey (MHS), a population-based study of cardiovascular disease (CVD) risk factors. METHODS: In a nested case-control study within MHS, 7 biomarkers were assayed in serum samples from 211 patients identified after 8-15 years of follow-up who died of cardiovascular causes (cardiovascular heart disease, stroke, congestive heart failure) and 253 controls matched on age, sex, and study year. Logistic regression analysis, adjusted for age, race, sex, education, study year, smoking, abdominal obesity, diabetes, serum total cholesterol, systolic blood pressure, previous hospitalization for a CVD event, and other significant biomarkers, was used to evaluate the relations of biomarkers relative to the odds of CVD mortality. RESULTS: Cases survived a median of 7.2 years after enrollment. Increased N-terminal pro-B type natriuretic peptide (NT-proBNP) (19% vs 4.3%), increased high-sensitivity C-reactive protein (hs-CRP) (71% vs 51%), and increased high-sensitivity cardiac troponin I (hs-cTnI) (8.7% vs 1.0%) were more common among cases than among controls (all P < 0.001 in unadjusted analyses). The adjusted odds of death were greater among cases compared to controls for increased NT-proBNP [odds ratio (OR) 5.67, 95% CI 2.17-15], hs-CRP (OR 1.73, 95% CI 1.03-2.89), and hs-cTnI (OR 8.53, 95% CI 1.68-43), and decreased ST2 (OR 1.92, 95% CI 1.05-3.48). CONCLUSIONS: When measured by an hs-cTnI assay, cTnI is a key biomarker associated with increased cardiovascular death in a community sample when evaluated in a multiple biomarker analysis.

Myeloperoxidase improves risk stratification in patients with ischemia and normal cardiac troponin I concentrations.

BACKGROUND: We assessed the ability of myeloperoxidase (MPO) to identify the risk for major adverse cardiac events (MACE) in patients who present with ischemic symptoms suggestive of acute coronary syndrome and have a normal cardiac troponin I (cTnI) value. METHODS: We used Siemens (n = 400) and Abbott (n = 350) assays to measure MPO and cTnI in plasma samples from 400 patients. Event rates (myocardial infarction, cardiac death, percutaneous coronary intervention, coronary artery bypass grafting) were estimated by the Kaplan-Meier method and compared with the log-rank statistic. RESULTS: At the 30-day follow-up, the adjusted hazard ratios for MACE were 3.9 (P < 0.001) for increased cTnI and 2.7 (P = 0.006) for increased MPO for the Siemens assays and were 5.5 (P < 0.001) for increased cTnI and 2.9 (P = 0.001) for increased MPO for the Abbott assays. Similar findings were observed with 6 months of follow-up. Patients who initially had a normal cTnI value and an increased Siemens MPO value demonstrated a higher rate of MACE at 30 days than those in whom both values were normal (16.1% vs 3.6%, P = 0.002) and 6 months (18.1% vs 5.0%, P = 0.002). Similarly, patients who had an increased Abbott MPO result demonstrated a higher MACE rate at 30 days (12.3% vs 3.9%, P = 0.03) and at 6 months (16.2% vs 5.1%, P = 0.01) than those with normal values. CONCLUSIONS: A combination of MPO and cTnI allowed the identification of a greater proportion of patients at risk for MACE than the use of cTnI alone. Increased MPO values remained predictive of future cardiac events even when the cTnI value was normal.

Measurement of B-type natriuretic peptide by two assays utilizing antibodies with different epitope specificity.

OBJECTIVES: To compare plasma BNP values determined by a conventional-type and a novel-type of BNP assays. DESIGN AND METHODS: Plasma samples (n=94) from HF patients were analyzed by the novel-type "Single Epitope Sandwich" (SES assay prototype) and the conventional-type Siemens ADVIA Centaur BNP assays. Both assays were calibrated using recombinant proBNP (expressed in E. coli). RESULTS: The SES assay measured 1.2- to 7.2-fold (2.1±0.9; mean, SD) greater BNP concentrations compared to the Siemens assay. A subset of six samples (6.4%) demonstrated the largest (3- to 7.2-fold higher) difference. CONCLUSIONS: The SES prototype assay appears to more accurately measure the absolute concentrations of BNP immunoreactive forms.

Defining the serum 99th percentile in a normal reference population measured by a high-sensitivity cardiac troponin I assay.

OBJECTIVES: This study determined the serum 99th percentile reference value for cTnI measured using the high sensitivity Erenna cTnI assay. DESIGN AND METHODS: Serum was obtained from healthy adults (n=348); aged 18-76 years of which 147 were males and 201 were females. Nonparametric analysis was performed to determine the 99th percentiles. RESULTS: For all subjects, the 99th percentile was 10.19 ng/L; mean concentration=1.45 ng/L, range=0.2 to 34.56 ng/L. By gender, the male and female 99th percentile values were as follows: male=16.58 ng/L, mean concentration=1.72 ng/L, and female=9.36 ng/L, mean concentration=1.25 ng/L, respectively (p=0.108). CONCLUSION: cTnI measured by the high-sensitivity Erenna cTnI assay measured 100% of normal subjects, allowing prospective diagnostic and risk assessment studies to be performed, which are essential for the early detection of cardiac disease and for the management of patients presenting with symptoms suggestive of acute coronary syndrome.

Role of monitoring changes in sensitive cardiac troponin I assay results for early diagnosis of myocardial infarction and prediction of risk of adverse events.

BACKGROUND: We sought to determine the diagnostic accuracy of the cardiac troponin I (cTnI) VITROS(R) Troponin I-ES assay for early detection of acute myocardial infarction (AMI) and for risk prediction of adverse events in patients with symptoms of acute coronary syndrome (ACS). METHODS: cTnI was measured on admission and approximately 6 h postadmission in 381 patients. The 99th percentile cTnI concentration (0.034 microg/L) and change [delta (delta)] between admission and follow-up concentrations were evaluated in diagnostic sensitivity and specificity calculations. Risk of cardiac event or death within 60 days was evaluated by Cox proportional hazards regression. RESULTS: AMI occurred in 52 patients. Diagnostic sensitivities (95% CI) of admission and follow-up cTnIs for AMI were 69% (55%-81%) and 94% (84%-99%), respectively. The corresponding specificities (95% CI) were 78% (73%-82%) and 81% (77%-85%), and ROC curve areas were 0.82 vs 0.96 (P < 0.001). Deltas between admission and follow-up cTnI >30% had a sensitivity of 75% (95% CI 61%-86%) and a specificity of 91% (95% CI 87%-94%). During follow-up, 1 cardiac death, 2 noncardiac deaths, 52 AMIs, 6 coronary artery bypass grafts, and 43 percutanous coronary interventions occurred in 62 patients. A delta cTnI >30%, when added to either initial cTnI >0.034 microg/L or follow-up cTnI >0.034 microg/L, improved risk stratification for cardiac event or death (P < 0.001). CONCLUSIONS: Admission cTnI measured by the VITROS ES assay is a sensitive biomarker for detection of AMI. Utilizing >30% cTnI delta in addition to either the baseline or follow-up concentration improved both specificity and risk assessment in patients presenting with symptoms of ACS.

Assessment of the multiple-biomarker approach for diagnosis of myocardial infarction in patients presenting with symptoms suggestive of acute coronary syndrome.

BACKGROUND: Cardiac troponin is the preferred biomarker for detecting acute myocardial injury and infarction (MI). We studied whether multiple biomarkers of numerous pathophysiological pathways would increase the diagnostic accuracy for detecting MI. METHODS: Seven biomarkers [myeloperoxidase, soluble CD40 ligand, placental growth factor, matrix metalloproteinase 9 (MMP-9), high-sensitivity C-reactive protein (hsCRP), cardiac troponin I (cTnI), N-terminal pro-B-type natriuretic peptide] and estimated glomerular filtration rate were measured in 457 patients presenting on admission with symptoms suggestive of acute coronary syndrome. Twenty-five patients (5.4%) received MI diagnoses. Clinical sensitivities and specificities were evaluated from 99th-percentile reference values. Forward and backward stepwise logistic regression modeling techniques were used to identify biomarkers that were independently predictive of MI. RESULTS: Biomarker sensitivities ranged from 20% to 96%, and specificities ranged from 19% to 89%. MMP-9 had the highest sensitivity, but its specificity was 19%. cTnI demonstrated a sensitivity of 72% (95% CI, 51%-88%) and a specificity of 89% (95% CI, 85%-92%). In multivariate models, cTnI (P < 0.001) and either hsCRP (P = 0.009) or MMP-9 (P = 0.03) were independently predictive of MI. Addition of hsCRP or MMP-9 increased the specificity to 95% (95% CI, 92%-97%) or 91% (95% CI, 88%-94%), respectively, but reduced the sensitivity to 56% (95% CI, 35%-76%) and 68% (95% CI, 47%-85%) relative to cTnI alone. CONCLUSIONS: Our findings indicate that the most clinically accurate biomarker for the early diagnosis of MI is the use of cTnI alone, rather than a multiple-biomarker approach, when an analytically robust cardiac troponin assay based on the 99th percentile is used.

Analytical characteristics of commercial cardiac troponin I and T immunoassays in serum from rats, dogs, and monkeys with induced acute myocardial injury.

BACKGROUND: Information is needed regarding analytical characteristics of cardiac troponin (cTn) assays used in preclinical studies. METHODS: We measured cTnI and cTnT in serum from normal animals and animals with induced myocardial injury [Sprague-Dawley (SD) and Wistar rats, beagle dogs, and rhesus (Rh) and cynomolgus (Cy) monkeys]. We evaluated the following assays: for cTnI, Abbott Architect, Bayer Centaur (first and second generation), Beckman Access, DPC Immulite, Dade Dimension, Ortho Vitros ES, Tosoh AIA, and species-specific enzyme immunoassays; for cTnT, Roche Elecsys. RESULTS: We found different species-specific responses for the troponin assays evaluated. Abbott, Bayer Ultra, Beckman, and Dade assays gave good responses across all species. In rats, weak responses were observed with DPC and Ortho, and no measurable response with Tosoh. In dogs, weak responses were observed with Tosoh cTnI, Roche cTnT, and species-specific cTnI. In cynomolgus monkeys, weak responses were observed with species-specific cTnI and Roche cTnT. Assay imprecision was < or = 20% at 3 or more examined cTn concentrations for Beckman (rat, dog, monkey), Dade (rat, dog, monkey), Abbott (rat, dog, monkey), Bayer first generation (dog), Bayer Ultra (rat, dog, monkey), Roche (monkey), DPC (dog, monkey), Ortho (dog, monkey), and Tosoh (dog, monkey) assays, whereas imprecision was < or = 20% at 2 or fewer concentrations for the Bayer first generation (rat, monkey), Roche cTnT (rat, dog), and DPC (rat) assays. CONCLUSIONS: Not all cTn assays are suitable for monitoring cTn in each animal species or strain. Individual assay characterization by animal species is needed to prevent misinterpretation of myocardial injury-based cardiac troponin findings.

Novel immunoassay for quantification of brain natriuretic peptide and its precursor in human blood.

BACKGROUND: Brain natriuretic peptide (BNP) is an unstable molecule that can rapidly lose immunologic activity in blood. Conventional sandwich BNP immunoassays use 2 antibodies specific to 2 different epitopes. Larger distances between epitopes are associated with a greater probability of proteolysis sites being located between the antibody-binding sites, and thus such assays have an increased susceptibility to underdetect BNP because of the increased likelihood of proteolytic degradation. The purpose of our study was to develop a sandwich immunoassay for the precise quantification of BNP and BNP precursor (proBNP) in human blood that is not susceptible to proteolysis. METHODS: Mice were immunized with an immune complex consisting of monoclonal antibody (MAb) 24C5 (specific for BNP peptide 11-22) and the entire BNP molecule. The MAb used in our assay (Ab-BNP2) recognizes the immune complex but neither free BNP nor MAb 24C5. RESULTS: We used MAbs 24C5 and Ab-BNP2 to develop a new type of sandwich BNP assay (the "single-epitope sandwich assay"), which requires only a short BNP fragment (fragment 11-22) for immunodetection. This assay recognizes both BNP and proBNP with the same efficiency and sensitivity and demonstrates both considerably less susceptibility to antigen degradation and greater stability of the measured antigen than conventional sandwich BNP immunoassays. CONCLUSIONS: We have developed this sensitive single-epitope sandwich assay for detecting BNP, proBNP, and their fragments in human blood. This assay appears promising for use in clinical studies to assist in triage, management, and outcomes assessment in heart failure patients.

Immunodetection of glycosylated NT-proBNP circulating in human blood.

BACKGROUND: Brain natriuretic peptide (BNP) or NT-proBNP (N-terminal fragment of BNP precursor) measurements are recommended as aids in diagnosis and prognosis of patients with heart failure. Recently it has been shown that proBNP is O-glycosylated in human blood. The goal of this study was to map sites on the NT-proBNP molecule that should be recognized by antibodies used in optimal NT-proBNP assays. METHODS: We analyzed endogenous NT-proBNP by several immunochemical methods using a broad panel of monoclonal antibodies specific to different epitopes of the NT-proBNP molecule. RESULTS: Treatment of endogenous NT-proBNP by a mixture of glycosidases resulted in significant improvement of the interaction between deglycosylated NT-proBNP and monoclonal antibodies (MAbs) specific to the mid-fragment of the molecule. MAbs specific to the N- and C-terminal parts of NT-proBNP (epitopes 13-24 and 63-76) were able to recognize glycosylated and deglycosylated protein with similar efficiency. CONCLUSIONS: The central part of endogenous NT-proBNP is glycosylated, making it almost "invisible" for the antibodies specific to the mid-fragment of the molecule. Thus sandwich assays using even one antibody (poly- or monoclonal) specific to the central part of the molecule could underestimate the real concentration of endogenous NT-proBNP. MAbs specific to the N- and C-terminal parts of NT-proBNP (epitopes 13-24 and 63-76) are the best candidates to be used in an assay for optimal NT-proBNP immunodetection.

Use of the Centaur TnI-Ultra assay for detection of myocardial infarction and adverse events in patients presenting with symptoms suggestive of acute coronary syndrome.

BACKGROUND: We determined the diagnostic accuracy of the Advia Centaur TnI-Ultra assay for detecting myocardial infarction (MI) and assessing risk of adverse events in patients presenting with ischemic symptoms suggestive of acute coronary syndrome. METHODS: We measured cardiac troponin I (cTnI) on admission and 6-24 h after admission (follow-up) in plasma specimens from 371 consecutive patients. The end point was the first of cardiac event or death within 60 days. We estimated survival curves using the Kaplan-Meier method and compared groups with the log rank statistic. RESULTS: MI was established in 49 patients (13%). Clinical sensitivities and specificities for MI based on the 99th percentile (0.04 microg/L) were 74% and 84%, respectively, on admission and 94% and 81% at follow-up. ROC curves showed significantly higher accuracy for MI in the follow-up specimen compared with admission (P = 0.001). Overall there were 2 cardiac deaths, 1 noncardiac death, 49 MIs, 7 coronary artery bypass grafts, and 36 percutaneous coronary interventions in 59 patients during follow-up. The event rate in those with cTnI <0.006 microg/L was significantly lower than in groups with cTnI 0.006-0.04 microg/L, >0.04-0.10 microg/L, or >0.10 microg/L (2.8% vs 11.1%, 24.1%, 55.1%, respectively; P <0.0001). Relative risks for the increasing cTnI cutoff groups were 3.9 (95% CI 1.2-13), 8.9 (2.4-34), and 25 (7.3-82) after adjustment for age, diabetes, history of hypertension, previous MI, and estimated glomerular filtration rate. CONCLUSIONS: The TnI-Ultra assay is a sensitive, early diagnostic biomarker for MI and an independent predictor of adverse events at any measurable cTnI in patients with symptoms of acute coronary syndrome.

Performance characteristics of the Architect brain natriuretic peptide (BNP) assay: a two site study.

INTRODUCTION: Brain natriuretic peptide (BNP) is produced by the ventricles of the heart and is a biomarker for heart failure. Several commercial assays are now available. We evaluated the performance characteristics of the ARCHITECT BNP assay. METHODS: We evaluated the limit of blank, limit of detection, linearity and imprecision. Method comparison studies were performed with 3 other automated BNP assays including the ADVIA Centaur, AxSYM, and UniCel DxI 800 methods. RESULTS: The mean LOB and LOD of the Architect assay were 3.5 and 5.8 ng/L, respectively. Imprecision studies yielded within run CVs of 1.1 to 5.1% and total CVs of 2.3 to 5.3% using human plasma based multi-constituent controls at concentrations of 92, 500, and 3500 ng/L. The maximum deviation from the target recovery for dilution linearity was 9.6%. Concordance with other BNP assays at a 100 ng/l cutoff was 91 to 98% and kappa statistics were 0.78 to 0.96. The mean difference between the Architect and Advia Centaur methods was positive. For the other methods, the mean difference with the Architect was negative. CONCLUSIONS: The Architect BNP assay shows good performance characteristics with total imprecision < or =5.3%. It agrees well with the Advia Centaur, AxSYM, and UniCel DxI BNP assays.

Use of the bioMérieux VIDAS troponin I ultra assay for the diagnosis of myocardial infarction and detection of adverse events in patients presenting with symptoms suggestive of acute coronary syndrome.

BACKGROUND: We demonstrate the performance of the bioMérieux VIDAS Troponin I Ultra assay for diagnostic accuracy for detection of myocardial infarction (MI) and risk stratification. METHOD: cTnI was measured in 545 patients from 2 clinical centers with symptoms suggestive of ACS at admission, with an additional specimen at 4-12 h (453 patients). The 99th percentile value (0.01 microg/l) was used to assess clinical accuracy for diagnosis of acute MI. Primary endpoint for risk stratification was first of cardiac event or death in 302 patients (one center) followed for 60 days. RESULTS: 157 (28.8%) patients ruled in for an MI during index hospitalization. Sensitivities and specificities were 88.1% (95% CI 81.9 to 92.4%) and 79.9% (CI 75.5 to 83.6%) for baseline and 100% (CI 96.5 to 100%) and 79.4% (CI 74.4 to 83.4%) for follow-up specimens. ROC curve areas increased from 0.912 (CI 0.879 to 0.944) at baseline to 0.994 (CI 0.988 to 0.999) at second sampling (n=453, p<0.01); with no differences between sites. Primary endpoint rate for the 223 patients (74%) with normal cTnI on presentation was lower than the 79 patients (26%) with cTnI>0.01 ug/l (5.9% vs. 42.3%, p<0.0001). The relative risk for the >0.01 ug/l group was 8.9 (CI 4.6 to 17). CONCLUSION: The VIDAS cTnI assay is a sensitive diagnostic method for the early detection of MI and predicts increased risk for adverse events in patients with symptoms suggestive of ACS.