Highly Sensitive Immunoassay for Long Forms of Cardiac Troponin T Using Upconversion Luminescence.

BACKGROUND: Long cardiac troponin T (cTnT) has been proposed to be a promising and more specific biomarker of acute myocardial infarction (AMI). As it represents a subfraction of circulating cTnT, detection of very low concentrations is a requirement. The aim of this study was to develop a novel, highly sensitive immunoassay for long cTnT. METHODS: A two-step sandwich-type immunoassay for long cTnT was developed, utilizing upconverting nanoparticles (UCNPs) as reporters. The limits of detection and quantitation were determined for the assay. Linearity and matrix effects were evaluated. Performance with clinical samples was assessed with samples from patients with non-ST elevation myocardial infarction (NSTEMI, n = 30) and end-stage renal disease (ESRD, n = 37) and compared to a previously developed time-resolved fluorescence (TRF)-based long cTnT assay and a commercial high-sensitivity cTnT assay. RESULTS: The novel assay reached a 28-fold lower limit of detection (0.40 ng/L) and 14-fold lower limit of quantitation (1.79 ng/L) than the previously developed TRF long cTnT assay. Li-heparin and EDTA plasma, but not serum, were found to be suitable sample matrixes for the assay. In a receiver operating characteristics curve analysis, the troponin ratio (long/total cTnT) determined with the novel assay showed excellent discrimination between NSTEMI and ESRD with an area under the curve of 0.986 (95% CI, 0.967-1.000). CONCLUSIONS: By utilizing upconversion luminescence technology, we developed a highly sensitive long cTnT assay. This novel assay can be a valuable tool for investigating the full potential of long cTnT as a biomarker for AMI. ClinicalTrials.gov Registration Number: NCT04465591.

Primary breast cancer biomarkers based on glycosylation and extracellular vesicles detected from human serum.

BACKGROUND: Breast cancer is a very common cancer that can be severe if not discovered early. The current tools to detect breast cancer need improvement. Cancer has a universal tendency to affect glycosylation. The glycosylation of circulating extracellular vesicle-associated glycoproteins, and mucins may offer targets for detection methods and have been only explored in a limited capacity. AIM: Our aim was to develop an approach to detect the aberrant glycosylation of mucins and extracellular vesicle-associated glycoproteins from human sera using fluorescent nanoparticles, and preliminarily evaluate this approach for the differential diagnosis of breast cancer. METHODS AND RESULTS: The assay involved immobilizing glycosylated antigens using monoclonal antibodies and then probing their glycosylation by using lectins and glycan-specific antibodies coated on Eu+3 -doped nanoparticles. Detection of mucin 1 and mucin 16 glycosylation with wheat germ agglutinin, and detection of the extracellular vesicle-associated CD63 were found to have better diagnostic ability for localized breast cancer than the conventional assays for mucin 1 and mucin 16 based tumor markers when the receiver operating characteristics were compared. CONCLUSIONS: These results indicate that successful differential diagnosis of primary breast cancer may be aided by detecting cancer-associated glycosylation of mucin 1 and mucin 16, and total concentration of CD63, in human serum.

Sensitive and quantitative detection of cardiac troponin I with upconverting nanoparticle lateral flow test with minimized interference.

Measurement of cardiac troponin I (cTnI) should be feasible for point-of-care testing (POCT) to diagnose acute myocardial infarction (AMI). Lateral flow immunoassays (LFIAs) have been long implemented in POCT and clinical settings. However, sensitivity, matrix effect and quantitation in lateral flow immunoassays (LFIAs) have been major limiting factors. The performance of LFIAs can be improved with upconverting nanoparticle (UCNP) reporters. Here we report a new methodological approach to quantify cTnI using UCNP-LFIA technology with minimized plasma interference. The performance of the developed UCNP-LFIA was evaluated using clinical plasma samples (n = 262). The developed UCNP-LFIA was compared to two reference assays, the Siemens Advia Centaur assay and an in-house well-based cTnI assay. By introducing an anti-IgM scrub line and dried EDTA in the LFIA strip, the detection of cTnI in plasma samples was fully recovered. The UCNP-LFIA was able to quantify cTnI concentrations in patient samples within the range of 30-10,000 ng/L. The LoB and LoD of the UCNP-LFIA were 8.4 ng/L and 30 ng/L. The method comparisons showed good correlation (Spearman's correlation 0.956 and 0.949, p < 0.0001). The developed UCNP-LFIA had LoD suitable for ruling in AMI in patients with elevated cTnI levels and was able to quantify cTnI concentrations in patient samples. The technology has potential to provide simple and rapid assay for POCT in ED setting.

Analytical techniques for multiplex analysis of protein biomarkers.

INTRODUCTION: The importance of biomarkers for pharmaceutical drug development and clinical diagnostics is more significant than ever in the current shift toward personalized medicine. Biomarkers have taken a central position either as companion markers to support drug development and patient selection, or as indicators aiming to detect the earliest perturbations indicative of disease, minimizing therapeutic intervention or even enabling disease reversal. Protein biomarkers are of particular interest given their central role in biochemical pathways. Hence, capabilities to analyze multiple protein biomarkers in one assay are highly interesting for biomedical research. AREAS COVERED: We here review multiple methods that are suitable for robust, high throughput, standardized, and affordable analysis of protein biomarkers in a multiplex format. We describe innovative developments in immunoassays, the vanguard of methods in clinical laboratories, and mass spectrometry, increasingly implemented for protein biomarker analysis. Moreover, emerging techniques are discussed with potentially improved protein capture, separation, and detection that will further boost multiplex analyses. EXPERT COMMENTARY: The development of clinically applied multiplex protein biomarker assays is essential as multi-protein signatures provide more comprehensive information about biological systems than single biomarkers, leading to improved insights in mechanisms of disease, diagnostics, and the effect of personalized medicine.

Cardiac troponin elevations in marathon runners. Role of coronary atherosclerosis and skeletal muscle injury. The MaraCat Study.

BACKGROUND: Marathon running is associated with transient risk of sudden cardiac death and high cardiac troponin levels are common after race. There is limited data whether coronary atherosclerosis or skeletal muscle injury are related to troponin release caused by strenuous exercise. We aimed to assess whether coronary artery calcification (CAC), plaque vulnerability or skeletal muscle injury relate to cardiac troponin T (cTnT) elevations after marathon race. METHODS: In this observational study, 40 male runners participating in Paavo Nurmi 2018 Marathon were recruited with an open email invitation to evaluate the prevalence of post-race cTnT elevations and their predictors. In addition to baseline and post-race laboratory investigations, 28 runners aged >44 years underwent CAC measurement with computed tomography. Coronary plaque vulnerability was evaluated by free pregnancy-associated plasma protein A (fPAPP-A) concentration and skeletal muscle injury by skeletal troponin I (skTnI) measurement. RESULTS: The post-marathon cTnT concentrations rose above the normal reference limit in 38 (95%) participants. A 10-fold increase in skTnI concentrations was observed and elevated post-race values were seen in all participants. The correlation between the post-race cTnT and post-race skTnI (rs = -0.26, p = 0.11) was non-significant. CAC was detected (Agatston score > 0) in 15 (53.6%) participants, with a median score of 2.0 (interquartile range [IQR] 80). There was no correlation between cTnT with CAC score or post-race fPAPP-A levels. CONCLUSIONS: Asymptomatic cardiac troponin elevations are common after prolonged strenuous exercise, but are not related to markers of coronary atherosclerosis, plaque vulnerability or skeletal muscle injury.

A Nanoparticle-Based Approach for the Detection of Extracellular Vesicles.

The analysis of extracellular vesicles (EVs) typically requires tedious and time-consuming isolation process from bio-fluids. We developed a nanoparticle-based time resolved fluorescence immunoassay (NP-TRFIA) that uses biotinylated antibodies against the proteins of tetraspanin family and tumor-associated antigens for capturing EVs from urine samples and cell culture supernatants without the need for isolation. The captured-EVs were detected either with Eu3+-chelate or Eu3+-doped nanoparticle-based labels conjugated either to antibodies against the tetraspanins or lectins targeting the glycan moieties on EVs surface. The NP-TRFIA demonstrated specific capturing and detection of EVs by antibodies and lectins. Lectin-nanoparticle based assays showed 2-10 fold higher signal-to-background ratio compared with lectin-chelate assays. The nanoparticle assay concept allowed surface glycosylation profiling of the urine derived-EVs with lectins. It was also applied to establish an assay showing differential expression of tumor-associated proteins on more aggressive (higher ITGA3 on DU145- and PC3-EVs) compared to less aggressive (higher EpCAM on LNCaP-EVs) PCa- cell lines derived-EVs. This NP-TRFIA can be used as a simple tool for analysis and characterization of EVs in urine and cell culture supernatants. Such approach could be useful in identification of disease-specific markers on the surface of patient-derived urinary EVs.

Direct Immunoassay for Free Pregnancy-Associated Plasma Protein A (PAPP-A).

BACKGROUND: Pregnancy-associated plasma protein A (PAPP-A), especially in its noncomplexed form (fPAPP-A), is linked to vulnerable atherosclerotic plaques and risk of cardiac events. An assay for sensitive detection of fPAPP-A has been lacking. Our aim was to develop and validate a direct fPAPP-A assay to meet this need. METHODS: Monoclonal antibodies binding exclusively fPAPP-A were produced by immunizing mice with recombinant PAPP-A. In the optimized immunoassay, we used an fPAPP-A-specific capture antibody together with a lanthanide-chelate-labeled monoclonal antibody recognizing all PAPP-A forms. The assay was evaluated with CLSI guidelines and compared to a 2-assay subtractive fPAPP-A approach. Clinical performance was assessed with acute coronary syndrome patients. RESULTS: The limits of detection and quantitation were 0.4 mIU/L and 1.3 mIU/L, respectively, and the assay was linear up to 1000 mIU/L (R2 = 0.999). Both serum and heparin plasma were suitable matrices, and the complexed form of PAPP-A caused no significant interference. Correlation between the developed assay and the 2-assay approach was fair (Pearson's r = 0.819). Median concentration in healthy individuals was 1.0 mIU/L. fPAPP-A concentration was higher in patients who had myocardial infarction or died during the 1-year follow-up period than in those who did not (1.13 mIU/L vs 0.82 mIU/L, P = 0.008, model adjusted with age and sex). fPAPP-A measured with this direct assay predicted this end point as well as (follow-up 1 year) or better (30 days) than the 2-assay fPAPP-A alone or in combination with cTnI. CONCLUSIONS: The new assay enables sensitive and reliable measurement of low cardiac-related fPAPP-A concentrations from blood samples.

Potentially pathogenic circulating autoantibodies to cardiac troponin are present in hemodialysis patients.

INTRODUCTION: Repetitive dialysis-induced cardiac injury is associated with elevated troponin levels, inflammation, and longitudinal reduction in cardiac function. Pathogenic autoantibodies to cardiac troponins (cTnAAb) produce inflammatory cardiomyopathy in murine models. This study aimed to explore the possibility that analogous autoimmune processes might occur in hemodialysis (HD) patients, by initially investigating cTnAAb prevalence, and exploring potential links with HD-induced myocardial stunning. METHODS: In 130 prevalent HD patients from two centers (Derby, UK; Turku, Finland), cTnAAb (immunoassay) and cardiac troponins were quantified. Sixty-four patients underwent serial echocardiography to assess myocardial stunning. FINDINGS: cTnAAb were present in 7% of patients. Dual positivity to cTnAAb and elevated cTn occurred in 3% and 6% for cTnI and cTnT, respectively. Patients with cTnAAb had significantly longer dialysis vintage (82 vs. 30 months, P = 0.024), higher cTnT (0.1 vs. 0.05 pg/mL, P = 0.04), cTnI (0.02 vs. 0.01 pg/mL, P = 0.029), and free PAPP-A (6.4 vs. 3.3 mIU/L, P = 0.038). DISCUSSION: This is the first description of cTnAAb in HD patients, which raises the possibility that longitudinal exposure to repetitive HD-induced cardiac injury may lead to further autoimmune-based myocardial insult.

Integrated Acoustic Separation, Enrichment, and Microchip Polymerase Chain Reaction Detection of Bacteria from Blood for Rapid Sepsis Diagnostics.

This paper describes an integrated microsystem for rapid separation, enrichment, and detection of bacteria from blood, addressing the unmet clinical need for rapid sepsis diagnostics. The blood sample is first processed in an acoustophoresis chip, where red blood cells are focused to the center of the channel by an acoustic standing wave and sequentially removed. The bacteria-containing plasma proceeds to a glass capillary with a localized acoustic standing wave field where the bacteria are trapped onto suspended polystyrene particles. The trapped bacteria are subsequently washed while held in the acoustic trap and released into a polymer microchip containing dried polymerase chain reaction (PCR) reagents, followed by thermocycling for target sequence amplification. The entire process is completed in less than 2 h. Testing with Pseudomonas putida spiked into whole blood revealed a detection limit of 1000 bacteria/mL for this first-generation analysis system. In samples from septic patients, the system was able to detect Escherichia coli in half of the cases identified by blood culture. This indicates that the current system detects bacteria in patient samples in the upper part of the of clinically relevant bacteria concentration range and that a further developed acoustic sample preparation system may open the door for a new and faster automated method to diagnose sepsis.

Elevated serum free pregnancy-associated plasma protein-A independently predicts mortality in haemodialysis patients but is not associated with recurrent haemodialysis-induced ischaemic myocardial injury.

BACKGROUND/AIMS: Pregnancy-associated plasma protein-A (PAPP-A) is a putative marker of atheroma instability and ischaemic myocardial stress prior to necrosis. Total PAPP-A (tPAPP-A) levels in acute coronary syndromes predict adverse outcomes. However, free PAPP-A (fPAPP-A) predominates in the circulation. Ischaemic haemodialysis (HD)-induced cardiac injury (myocardial stunning) is common and is associated with markers of myocardial necrosis, inflammation, cardiovascular events and mortality. Coronary plaque instability in pathophysiology of HD-induced myocardial stunning has not been studied. We aimed to investigate the relationship of fPAPP-A with stunning and mortality. METHODS: 130 prevalent patients from two HD centres (Finland and UK) were studied. Pre-HD free, complexed and total PAPP-A were measured by immunoassay. A subset of 62 patients underwent echocardiography to assess HD-induced myocardial stunning. The mean duration of follow-up was 407 ± 98 days. RESULTS: fPAPP-A was elevated (median: 3.45 mIU/l) and correlated with dialysis vintage (r = 0.391, p < 0.001), cardiac troponin T (cTnT; r = 0.29, p = 0.001) and cardiac troponin I (cTnI; r = 0.22, p = 0.01). PAPP-A was not related to stunning. Dialysis vintage and cTnT independently predicted Ln fPAPP-A (model R = 0.463). fPAPP-A, cTnT and age independently predicted death (Nagelkerke R(2) = 0.362). CONCLUSIONS: fPAPP-A, a novel predictor of HD-related mortality, demonstrates better prognostic power than tPAPP-A. Coronary plaque instability may contribute to sub-lethal myocardial injury, but may not be critical in pathogenesis of HD-induced ischaemic cardiac injury.

Novel sensitive cardiac troponin I immunoassay free from troponin I-specific autoantibody interference.

BACKGROUND: Cardiac troponins (cTnI and cTnT) are the recommended biomarkers of myocardial infarction. As cTn-specific autoantibodies (cTnAAb) can interfere with the cTn detection by state-of-the-art cTnI assays, our objective was to develop a sensitive cTnI immunoassay free from this analytical interference. METHODS: The assay used antibody-coated spots containing three capture Mabs/Fabs directed against the N-terminus, midfragment and C-terminus of cTnI and a europium chelate-labeled tracer Mab against the C-terminus. Following a 3-h sample incubation and washing, cTnI was quantified by time-resolved fluorometry. RESULTS: The limit of detection (LoD) was 2.9 ng/L and the assay was linear up to 50,000 ng/L. The total precision of 10% CV was not reached, but 20% CV was reached at 10 ng/L. Mean cTnI (10-50,000 ng/L) recoveries were 100% and 119% in three cTnAAb-positive and two cTnAAb-negative individuals, respectively, verifying the interference resistance of the antibody design used. On average, Architect hs-cTnI assay gave seven-fold higher cTnI concentrations than the new assay but the correlation between the assays was good (r=0.958). Of apparently healthy individuals (n=159), 18% had measurable cTnI values (>LoD) and 10% were cTnAAb-positive. The proportion of measurable cTnI values, however, was significantly higher in cTnAAb-positive individuals (13/16, median cTnI 8.5 ng/L) than in cTnAAb-negative individuals (15/143, median cTnI

Autoantibody prevalence with an improved immunoassay for detecting cardiac troponin-specific autoantibodies.

BACKGROUND: Cardiac troponin-specific autoantibodies (cTnAAb) can interfere with the measurement of cardiac troponin I (cTnI) by immunoassays used for the diagnosis of myocardial infarction (MI). Here, an improved version of a previous autoantibody assay was validated and used to evaluate the cTnAAb prevalence in a cohort of consecutive chest pain patients presenting to an emergency department. METHODS: Admission samples from 510 patients with suspected MI were analyzed in parallel with two sandwich-type cTnAAb assays based on different cTnI epitopes used to capture cardiac troponin-bound cTnAAbs. RESULTS: Sample-specific backgrounds were lower for the new assay than for the old assay (median 1225 vs. 2693 counts, p<0.001). Net signals of cTnAAb-positive samples were higher for the new assay than for the old assay (median 5076 vs. 3921 counts, p<0.001). Of all patients, 9.2% were cTnAAb-positive for the new assay and 7.3% for the old assay (p=0.013). Previous cardiac problems were not associated with cTnAAb status and cTnAAb status did not correlate with the 12-month outcome. CONCLUSIONS: With our new and more sensitive autoantibody assay, approximately one out of ten patients who presented to the initial cardiac triage had detectable amounts of cTnAAbs in the circulation. Because these cTnAAbs can interfere with state-of-the-art cTnI assays, their high prevalence should be acknowledged by clinical chemists, physicians, and kit manufacturers.

Epitope specificity and IgG subclass distribution of autoantibodies to cardiac troponin.

BACKGROUND: Autoantibodies to cardiac troponins (cTnAAbs) can interfere with the measurement of cardiac troponin I (cTnI) by immunoassays for the diagnosis of myocardial infarction. Therefore, we determined the cTnI binding sites and IgG subclasses of circulating cTnAAbs. METHODS: We studied epitope specificity with sandwich-type immunoassays by measuring the recovery of troponin complex added to 10 cTnAAb-negative and 10 cTnAAb-positive sera from healthy volunteers. To study the IgG subclasses, we analyzed admission and 3-month follow-up sera from chest pain patients with a reference assay measuring total IgG (14 cTnAAb negative and 14 cTnAAb positive at 3 months) and with 4 subclass-specific assays measuring exclusively IgG subclasses 1-4. RESULTS: Mean recoveries of troponin complex in cTnAAb-positive samples for single cTnI epitopes ranged from 37% to 211%, being lowest for the cTnI midfragment (aa 30-110). However, the lowest sample-specific recoveries, 4%-92%, showed that none of the studied epitopes completely escaped the cTnAAb-related interference. Eight chest pain patients of the cTnAAb-positive group became positive between sampling points, and according to all 5 cTnAAb assays, specific signals were generally higher at follow-up. IgG4, with the highest prevalence, was detected in 68% of samples in the cTnAAb-positive group. CONCLUSIONS: IgG subclass studies confirm that cTnAAb formation may be triggered/boosted in acute cardiac events. This new information about the epitope specificity of cTnAAbs should be used to reevaluate existing recommendations regarding use of midfragment epitopes in cTnI assays. To circumvent the negative interference of the highly heterogeneous cTnAAbs, use of 3 or more unconventionally selected epitopes should be considered.

Troponin-specific autoantibody interference in different cardiac troponin I assay configurations.

BACKGROUND: Autoantibodies to cardiac troponins (cTnAAb) can interfere with the measurement of cardiac troponin I (cTnI) by immunoassays. The aim of this study was to explore the degree of cTnAAb interference in different cTnI assay configurations. METHODS: Ternary troponin complex was added into samples (serum or plasma, n = 132, 68% cTnAAb positive) from individuals without known cardiac conditions. The recovery of cTnI was then measured with 6 investigational cTnI assays (2, 3, or 4 antibodies per assay). Three of these assays were then selected for further comparison by use of samples (plasma, n = 210, 33% cTnAAb positive) from non-ST-elevation acute coronary syndrome patients in the FRISC-II (FRagmin/Fast Revascularisation during InStability in Coronary artery disease) cohort. Finally, these results were compared to those obtained with 3 commercial cTnI assays. RESULTS: Analytical recoveries varied widely among the 6 investigational assays. Notably the low recoveries (median 9%) of the midfragment-targeting reference assay were normalized (median 103%) with the use of the 4-antibody assay construct (3 capture, 1 tracer antibody) with only 1 antibody against a midfragment epitope. Reduced analytical recoveries correlated closely with measured autoantibody amounts. cTnI concentrations from cTnAAb-positive patient samples determined with 3 investigational assays confirmed the reduced concentrations expected from the low analytical recoveries. The results from the commercial cTnI assays with antibody selections representative for contemporary assay constructs revealed a similar underestimation (up to 20-fold) of cTnI in cTnAAb-positive samples. CONCLUSIONS: A novel cTnI assay deviating from the conventional IFCC-recommended midfragment approach substantially improves cTnI detection in samples containing cTnAAbs.

Studies on the effects of heparin products on pregnancy-associated plasma protein A.

BACKGROUND: Intravenous low molecular weight (LMWH) and unfractionated heparin (UFH) increase the circulating concentrations of pregnancy-associated plasma protein A (PAPP-A), a novel cardiac risk marker, in haemodialysis and coronary angiography patients. METHODS: To further investigate the mechanisms of heparin effects, free PAPP-A was analysed in serial serum samples collected during haemodialysis (intravenous LMWH), carotid endarterectomy or abdominal aortic aneurysm surgery (intravenous UFH), treatment at intensive care unit (subcutaneous LMWH), and coronary angiography (intravenous bivalirudin). PAPP-A was extracted from plaque tissue samples of endarterectomy and aneurysm patients. The interaction between heparin products and free PAPP-A was studied with gel filtration. RESULTS: After intravenous UFH and LMWH free PAPP-A increased significantly but bivalirudin had no effect. After LMWH bolus in haemodialysis patients 85% of free PAPP-A was cleared with a half-life of 13.1 min and the rest with a half-life of 96.6 min. Subcutaneous LMWH led to lower and slower free PAPP-A elevation. PAPP-A extracted from plaque tissues was in free form and extraction was strongly enhanced by LMWH. Heparin products increased the molecular size of free PAPP-A. CONCLUSIONS: The heparin-induced PAPP-A elevation is seen in various patients and should be taken into account when PAPP-A is studied as a biomarker.

Autoantibodies to cardiac troponin in acute coronary syndromes.

BACKGROUNDS: In a recent small study, patients with autoantibodies to cardiac troponin (cTnaAb) had higher cardiac troponin I (cTnI) release during an episode of acute coronary syndrome (ACS) than patients without cTnaAb and continued to have higher long-term levels of cTnI. However, the prognostic importance of the occurrence of cTnaAb is unknown. METHODS: In 957 nonST-elevation ACS patients cTnaAb and cTnI were analyzed at randomization and after 6 months. Outcomes were assessed through 5 years. RESULTS: Seven and 11% of the patients were cTnaAb positive at inclusion and 6months, respectively. The cardiac troponin I (cTnI) concentration at inclusion was independently associated with the development of cTnaAb (OR 1.53, 95% CI 1.25-1.88). The presence of cTnaAb was associated with an increased cTnI level at 6 months (OR 2.39, 95% CI 1.50-3.81). cTnaAb was not independently associated with death and AMI during follow-up (HR 0.97, 95% CI 0.61-1.54). CONCLUSION: Development of cTnaAb after an episode of nonST-elevation ACS is associated with the acute myocardial damage, but occurs only in a minority of patients. Furthermore, the presence of cTnaAb is associated with chronically elevated cTnI concentrations. However, the occurrence of cTnaAb is not associated with an adverse long-term prognosis.

Free vs total pregnancy-associated plasma protein A (PAPP-A) as a predictor of 1-year outcome in patients presenting with non-ST-elevation acute coronary syndrome.

BACKGROUND: The free fraction of pregnancy-associated plasma protein A (FPAPP-A) was found to be the PAPP-A form released to the circulation in acute coronary syndrome (ACS). We estimated the prognostic value of FPAPP-A vs total PAPP-A (TPAPP-A) concentrations in forecasting death and nonfatal myocardial infarction (combined endpoint) in patients with non-ST-elevation ACS. METHODS: We recruited 267 patients hospitalized for symptoms consistent with non-ST-elevation ACS and followed them for 12 months. FPAPP-A, TPAPP-A, C-reactive protein (CRP), and cardiac troponin I (cTnI) were measured at admission; cTnI was also measured at 6-12 h and 24 h. Because of the recently shown interaction between PAPP-A and heparin, we excluded patients treated with any heparin preparations before the admission blood sampling. RESULTS: During the follow-up, 57 (21.3%) patients met the endpoint (22 deaths and 35 nonfatal myocardial infarctions). According to FPAPP-A (<1.27, 1.27-1.74, >1.74 mIU/L) and TPAPP-A (<1.98, 1.98-2.99, >2.99 mIU/L) tertiles, this endpoint was met by 12 (13.5%), 18 (20.2%), 27 (30.3%) (P = 0.02), and 17 (19.1%), 17 (19.1%), 23 (25.8%) (P = 0.54) patients, respectively. After adjusting for age, sex, diabetes, previous myocardial infarction, and ischemic electrocardiogram (ECG) findings, FPAPP-A >1.74 mIU/L [risk ratio (RR) 2.0; 95% CI 1.0-4.1, P = 0.053), increased cTnI, and CRP >/=2.0 mg/L were independent predictors of an endpoint. The prognostic performance of TPAPP-A was inferior to that of FPAPP-A. CONCLUSIONS: FPAPP-A seems to be superior as a prognostic marker compared to TPAPP-A, giving independent and additive prognostic information when measured at the time of admission in patients hospitalized for non-ST-elevation ACS.

Autoantibodies to cardiac troponin associate with higher initial concentrations and longer release of troponin I in acute coronary syndrome patients.

BACKGROUND: Cardiac troponin (cTn) is an established marker of myocardial infarction. Pronounced heterogeneity and the minute amounts released into the circulation constitute significant challenges for cTn detection. Recently, autoantibody formation to cTn was shown to be common and to interfere with immunoassay performance. In this study, we investigated cTn autoantibodies and cardiac troponin I (cTnI) in acute coronary syndrome (ACS) patients over a 1-year period after the index event. METHODS: We used a second-generation cTnI assay designed to reduce the interference of cTn autoantibodies. The assay for cTn autoantibodies used 2 anti-cTnI antibodies to capture the ternary cTnI-complex, enabling unrestricted binding of the autoantibodies, which were detected with a labeled antihuman IgG antibody. We analyzed serum samples from 81 non-ST-elevation ACS patients taken at admission and after 1 week and 3 and 12 months. RESULTS: We found 14 cTn autoantibody-positive patients (21%) among the 67 cTnI-positive and none among the 14 cTnI-negative patients. Nine were autoantibody-positive at admission, and 5 became positive at 1 week. Autoantibody signals significantly increased in the 1-week and 3-month samples. At all time points, cTnI was significantly increased in the autoantibody-positive group relative to the negative group. Persistent cTnI elevations at 3 and 12 months were seen in the patients already autoantibody positive at admission. CONCLUSIONS: During ACS, patients with cTn autoantibodies have higher cTnI release and therefore larger myocardial damage than patients without autoantibodies. Their cTnI release also lasts longer, at least months. The possible prognostic impact of these observations must be evaluated in larger clinical cohorts.