Cardiac markers: present and future

Point-of-care paper-based analytical device for potentiometric detection of myoglobin as a cardiovascular disease biomarker

One of the cardiac biomarkers, myoglobin (Mb), is important in the rapid identification of cardio-vascular disorders. Therefore, point-of-care monitoring is essential. Pursuing this goal, a robust, reliable, and affordable paper-based analytical apparatus for potentiometric sensing has been developed and characterized. The molecular imprint technique was used to create a customized biomimetic antibody for myoglobin (Mb) on the surface of carboxylated multiwalled carbon nanotubes (MWCNT-COOH). This was accomplished by attaching Mb to carboxylated MWCNTs' surfaces and then filling the empty spaces through the mild polymerization of acrylamide in N,N-methylenebisacrylamide and ammonium persulphate. The modification of the MWCNTs' surface was verified by SEM and FTIR analysis. A hydrophobic paper substrate coated with fluorinated alkyl silane (CF₃(CF₂)₇CH₂CH₂SiCl₃, CF¹⁰) has been coupled with a printed all-solid-state Ag/AgCl reference electrode. The presented sensors showed a linear range of 5.0 × 10^-8 to 1.0 × 10^-4 M with a potentiometric slope of -57.1 ± 0.3 mV decade^-1 (R² = 0.9998) and a detection limit of 28 nM at pH 4. Compared to creatinine, sucrose, fructose, galactose, sodium glutamate, thiamine, alanine, ammonium, uric acid, albumin, glutamine, guanine, troponine T, and glucose, the sensor showed good selectivity for Mb. It demonstrated a good recovery for the detection of Mb in several fake serum samples (93.0-103.3%), with an average relative standard deviation of 4.5%. The current approach might be viewed as a potentially fruitful analytical tool for obtaining disposable, cost-effective paper-based potentiometric sensing devices. These types of analytical devices can be potentially manufacturable at large scales in clinical analysis.

An Optimized Colorimetric Readout Method for Lateral Flow Immunoassays

Despite its broad penetration of various markets, the quantitative lateral flow immunoassay (LFIA) suffers from sensitivity issues in some cases. To solve this problem, an optimized colorimetric readout method for LFIA quantification is proposed in this study. An assay reader device utilizing a color camera and an analysis method using a Bayer filtered image were developed. Spectrometric measurements of the assay test line were performed to determine the color channel that contains the test line information and effectively minimizes noise. The change in the intensity ratio with increasing concentration of the target substance in the sample was largest in the green channel. The linear range of the output curve ranged from 0 to 10 ng/mL, and the detection limit was 2 ng/mL. The suggested instrumentation and analysis methods are expected to effectively resolve the low-sensitivity problems of the former LFIA systems and to offer other prospective functionalities for LFIA quantification.

Evaluation of ischemia-modified albumin in myocardial infarction and prostatic diseases

BACKGROUND

Ischemia-modified albumin (IMA) has been shown to be a rapidly rising and sensitive biochemical marker for the diagnosis of myocardial ischemia. In this study, we evaluated the levels of IMA in myocardial infarction and prostate diseases, as well as the influence of HDL cholesterol levels on C-reactive protein (CRP) and IMA levels.

METHODS

A total of 27 patients with myocardial infarction (MI), 102 patients with benign prostatic hyperplasia (BPH), 84 patients with prostate cancer (PCA), and 21 healthy subjects were enrolled in this study. IMA levels were measured in whole studied patients. Cardiac troponin I (cTnI), cholesterol, HDL cholesterol, and CRP were measured in MI and control groups.

RESULTS

IMA values were significantly higher in patients with MI (0.5215+/-0.0241 ABSU) and BPH (0.4150+/-0.0156 ABSU) in comparison to control subjects (0.3381+/-0.0194 ABSU). IMA and CRP were higher in MI group, especially in patients with HDL cholesterol levels lower than 38 mg/dL. The ability of IMA to discriminate myocardial infarction was higher than CRP. Significant correlations between CRP and HDL, CRP and IMA, and HDL and IMA were reported.

CONCLUSIONS

IMA and CRP increase in myocardial damage, and the decrease of HDL cholesterol appears to enhance the inflammatory response. IMA also increase in benign prostate hyperplasia and this finding suggests that the diagnosis of prostate diseases must be considered on evaluation of IMA as a marker of cardiac ischemia.

Diagnosis of acute myocardial infarction: CK-MB versus cTn-T in Indian patients

The comparative diagnostic efficacy of two cardiac markers: CK-MB and cTn-T, has scarcely been investigated in Indian patients of acute myocardial infarction. The present study was conducted for the same objective. The present study comprised of 59 patients. Males were 44 (75%) and females were 15 (25 %). The age of patients ranged from 32-84 years with mean age of 62.8 yrs. The mean age of males and females were 60 and 63 yrs respectively. All patients presented with history of chest pain with a 12 leads ECG proven MI (ST Elevation, discordant T-waves). CK-MB was estimated in peripheral blood samples at 0,24,48 and 72 hours by an autoanalyzer. Following 12 hours of admission bed side Troponin-T test was done employing cTn-T marker kit. Initially (0 hr), in 50% patients CK-MB was elevated. By end of 24 hours all the patients were CKMB positive and peak level was attained at 24 hrs. Then it tended to decline over next 48 hrs. There were no false positive or negative results. The cTn-T test was positive only in 22 % of ECG positive infarctions. However, the cTn-T positive cases were always accompanied by a higher CK-MB levels. A significantly lower cTn-T positive cases in Indian patients can only be attributed to some difference in amino acid sequence of Indian cTn-T and occidental cTn-T. A larger study from other Indian cardiac centers can either substantiate or contradict our results.

Detection of Cardiac Biomarkers Using Micellar Electrokinetic Chromatography and a Cleavable Tag Immunoassay

Biomarkers provide clinicians with an important tool for disease assessment. Many different biomarkers have been discovered, but few of them suffice as stand-alone indicators for disease presence or prognosis. Because no single biomarker can be relied upon for accurate disease detection there has been a substantial push for new multianalyte screening methods. Furthermore, there is a need to push assays toward a point-of-care technology to reduce the time between clinical analysis and medical intervention and minimize artifacts created during sample storage. There currently are, however, few inexpensive multianalyte methods for disease detection that can function in a point-of-care setting. A new approach which bridges the gap between traditional immunoassays and high-density microarrays by utilizing microfluidics, immunoassays, and micellar electrokinetic chromatography (MEKC) is discussed here. This chemistry, the cleavable tag immunoassay (CTI), is a low- to medium-density heterogeneous immunoassay designed to detect 1-20 analytes simultaneously. Although similar to traditional sandwich immunoassays, this approach is unique because the signal is not imaged on the surface; instead, a fluorescent tag is chemically cleaved from the antibody and analyzed by microchip MEKC. In this report, the CTI chemistry is used for the detection of four cardiac biomarkers elevated in acute myocardial infarction. Limit of detection (LOD) and dynamic range are reported for all biomarkers with LODs on the order of low nanograms per milliliter to low picograms per milliliter. Most importantly, the dynamic range for each of the biomarkers spans the boundary between normal and elevated levels. Finally, elevated marker levels were measured in spiked human serum samples.

New biochemical markers: from bench to bedside

BACKGROUND

Evaluation of patients presenting to hospital with chest pain or other signs or symptoms suggesting acute coronary syndrome (ACS) is problematic, time-consuming and sometimes expensive, even if new biochemical markers, such as troponins, have improved the ability to detect cardiac injury. However, patients with normal troponin values are not necessarily risk-free for major cardiac events.

METHODS

Recent investigations indicate that the overall patient risk may be assessed earlier than before, thanks to new knowledge acquired concerning the pathobiology of atherosclerosis and molecular events involved in the progression of disease, thus allowing the development of new biochemical markers. Some selected markers are released during the different phases of development of cardiovascular disease and may be useful for the diagnosis of patients with cardiovascular disease. In particular, the identification of emerging markers that provide relevant information on the inflammatory process, and the development of biomarkers whose circulating concentrations suggest the status of plaque instability and rupture, seems to be of particular value in prognosis and risk stratification. The overall expectations for a cardiovascular biochemical marker are not only its biological plausibility but also the availability at a reasonable cost of rapid, high quality assays, and their correct interpretation by clinicians using optimal cut-offs.

CONCLUSION

The crossing from bench to bedside for each new marker discovered, must be associated with concurrent advances in the characterization of analytical features and the development of routine assay, in the assessment of analytical performance and in interpretative reporting of test results as well as in the training of physicians to use the array of biomarkers available appropriately and to interpret them correctly. This approach calls for the coordinated support of clinicians, technology experts, statisticians and the industry so that new biochemical developments can be of optimal value.

Multi-analyte immunoassay using cleavable tags and microchip micellular electrokinetic chromatography

A new multi-analyte immunoassay designed to screen for several biomarkers using cleavable tag chemistry and micellular electrokinetic chromatography was evaluated.

Lack of association between cardiac troponin T and D-dimer in the evaluation of myocardial damage

Acute myocardial infarction (AMI) disrupts cardiac cell membranes, releasing intracellular cardiac proteins into the vascular system. Some of these proteins, including the cardiac troponin subunits T and I, have proven useful for diagnosing myocardial damage. Intracoronary thrombosis plays a key role in the pathogenesis of AMI, and the formation of an occlusive thrombus usually precedes the development of myocardial damage. To evaluate whether there is an association between the size of intracoronary thrombosis and myocardial damage, we analyzed D-dimer and cTnT levels in blood samples from patients suspected to have myocardial damage. We investigated 102 patients who were admitted to emergency service for suspected myocardial damage. D-dimer was assessed with the use of the immunoassay Liatest D-dimer, and cTnT levels were measured with an electrochemiluminescence immunoassay (Troponin T STAT). D-dimer levels were lower in patients with cTnT < 0.01 than in patients presenting cTnT > 0.01 ng/mL. We investigated the relationship between D-dimer and cTnT levels in the patients with cTnT > 0.01 ng/mL (0.40 +/- 0.10 ng/mL), and no significant agreement (r = 0.20, P > 0.05) was observed. The levels of D-dimer were not associated with the levels of cTnT in patients with cTnT > 0.01 ng/mL.

Fish oil before cardiac surgery: neutrophil activation is unaffected but myocardial damage is moderated

Could pre-operative dietary intervention with fish oil reduce neutrophil activation and myocardial damage associated with cardiopulmonary bypass (CPB)? Patients were randomised to receive either 8 g/day fish oil (n=22) or placebo (n=18) for 6 weeks. Neutrophil activation, apoptosis and cardiac damage were measured. Demographics and operative variables were similar. Fish oil diet decreased plasma VLDL from 0.69+/-0.34 to 0.51+/-0.24 mmol/l and triglycerides from 1.68+/-0.70 to 1.39+/-0.54 mmol/l. HDL cholesterol increased from 0.94+/-0.27 to 1.03+/-0.26 mmol/l demonstrating significant treatment effects (P=0.007, 0.02 and 0.0003, respectively) as well as compliance with treatment. There were no significant differences in ex vivo N-formyl-methionyl-leucyl-phenylalanine-stimulated neutrophil superoxide anion generation or myeloperoxidase release at recruitment, pre-operatively and at end-CPB. Apoptosis at end-CPB was equally reduced in both groups from 23+/-9% to 13+/-4% in the fish oil group (P<0.001) and 35+/-14% to 15+/-3% in the placebo group (P=0.001). At end-CPB overall troponin I levels averaged 0.91+/-0.60 ng/ml which clearly exceeded diagnostic levels (0.15 ng/ml). At 24h troponin I fell significantly in the fish oil group to 46+/-23% of end-CPB levels (P=0.0002) whereas it peaked in the placebo group to 107+/-72% (P=0.098 vs. end-CPB); this difference was significant: P=0.013. At 48 h the placebo-treated patients had higher troponins but not significantly so (P=0.059). Area-under-the-curve analysis did not conclusively support this (P=0.068). We conclude that fish oil did not significantly decrease post-CPB neutrophil activation (as detected ex vivo) but may moderate post-operative myocardial damage.

Development of a displacement immunoassay for human heart-type fatty acid-binding protein in plasma: the basic conditions

To risk-stratify patients with chest pain who are admitted to emergency rooms and for whom initial evaluation is not conclusive, the use of cardiac markers has become a standard procedure. A recently introduced early plasma marker for acute myocardial infarction (AMI) is the 14.5-kDa cytoplasmic heart-type fatty acid-binding protein (FABP). To fully exploit its early release from injured myocardium, a rapid method for repeated measurements or continuous monitoring of FABP in plasma is desirable. Such an on-line method could be an immunosensor based on displacement. The aim of the present study was to further investigate the principles underlying the displacement assay of FABP, both in buffer and in plasma. Batches of sepharose-bound FABP were loaded with an antibody-horseradish peroxidase (HRP) conjugate (anti-FABP). Continuous measurement of FABP was mimicked by repeated addition of FABP containing solutions followed by several washing steps. In the presence of free FABP the antibody-HRP complex dissociated and was subsequently quantified. Significant displacement in the presence of free FABP was observed in both buffer and human plasma. Anti-FABP could be intermittently displaced in the same batch, for at least 9 h, and the displacement was concentration-dependent. These results show the feasibility of a sensor based on the displacement principle to be used for the diagnosis of AMI in emergency medicine.

Interpretative comments and reference ranges in EQA programs as a tool for improving laboratory appropriateness and effectiveness

INTRODUCTION

Laboratory information is generated when a meaning is given to certain data. This is usually achieved by comparing a laboratory test result with the reference range/decisional limit (RL), and by providing consultation for the interpretation of data, advice, and follow-up testing.

AIM

In this paper, we investigate factors affecting the conversion of data into useful information with regard to biochemical markers of myocardial damage (CK-MB mass, myoglobin, and troponins), in view of their importance in detecting myocardial necrosis. Our aim was to report results obtained in order to verify the consensus between laboratories with reference to interpretative comments and the reference ranges/decisional limits added to clinical reports.

METHODS

A questionnaire and simulated medical reports on three different patients were distributed to participants (94 laboratories) in the 2001 cycle of the External Quality Assessment (EQA). Moreover, we analysed 113 medical reports sent by laboratories during the most recent EQA cycle 2002, and checked the number of different RLs used, both independent and within the diagnostic system used. We also compared each laboratory result of a control sample, obtained in the 2002 cycle, with declared RL in order to verify the clinical significance of results ("normal" or "pathological") for troponin I and CK-MB.

RESULTS

Our findings show that few laboratories regularly add interpretative comments to medical reports. On the contrary, they cooperate with clinicians who require consultation, advice, and information for the appropriate use of biochemical markers. There is a general consensus among participants regarding probable syndromes suggested by the interpretation of the same result and most laboratories also agree on further investigations to be carried out for several diseases. Concerning RL, the data demonstrate that numerous different RLs are used to report the results of the biochemical markers evaluated, both when considered independent of the diagnostic system used and within the diagnostic system used.

DISCUSSION AND CONCLUSIONS

The biochemist does not have the opportunity to verify the efficacy of the interpretation that he/she provided. An audit of this activity is therefore required to allow the laboratory to monitor its own performance and to assure good practice. The evaluation of interpretative comments, through specific surveys, should be a prime objective of EQA organisers. Well-designed EQA programs can, moreover, support laboratories in establishing appropriate RL and in verifying the clinical significance of their results with respect to that of other laboratories. Our survey on interpretative comments and the analysis of the RLs further demonstrate how laboratory medicine can contribute to the objective evaluation of the patients' health status.

Coagulation indicators in chronic stable effort angina and unstable angina: relationship with acute phase reactants and clinical outcome

The aim of the study was to evaluate which pattern of coagulation indicators characterizes unstable angina and, particularly, its relationship with short-term prognosis. Forty patients with unstable angina (UA Group) at admission in the intensive care unit, 40 patients with chronic stable effort angina (SEA Group), and 20 age- and sex-matched healthy controls were studied. Blood coagulation indicators were fibrinogen, prothrombin fragment F1 + 2 (F1 + 2), thrombus precursor protein (TpP), and D-dimer. C reactive protein (CRP) and cardiac Troponin I (cTnI) have also been determined and compared. Patients in the UA Group were followed for in-hospital adverse events (sudden death, acute myocardial infarction and angina refractory to medical therapy). CRP, D-dimer and cTnI plasma levels were significantly lower in the SEA Group than in the UA Group; the same trend was found for fibrinogen and F1 + 2 plasma levels, although not statistically significant. The TpP was similar in all groups. The control group showed the lowest levels for all indicators. Within the UA Group, 17 patients developed adverse events during hospitalization; F1 + 2, D-dimer, cTnI and CRP plasma levels were higher in these patients than in those with good outcome. Relative risks for adverse events associated with the highest tertile of D-dimer, cTnI, and CRP plasma levels were 8.4 (95% confidence interval, 1.5-48.9), 6.7 (95% confidence interval, 1.1-38.6) and 5.2 (95% confidence interval, 1.1-25.2), respectively. D-Dimer is significantly increased in patients with unstable angina and, in particular, in those who develop an adverse event.

Stability of cardiac troponins and CK-MB mass isoenzyme

The stability of an analyte can have an important influence on its diagnostic performance and therefore should be documented before an analyte is introduced into routine practice. The stability of creatine kinase MB isoenzyme (CK-MB), troponin I and troponin T was studied by incubating samples at temperatures between 26 degrees C and 39 degrees C for periods up to 5400 min. Arrhenius plots were made which showed that all three proteins demonstrated a rapid decrease in stability between 15 degrees C and 20 degrees C. The activation energies for CK-MB, troponin I and troponin T were 7.7, 6.34 and 6.34 cal/mol, respectively.