Recent approaches in standardization of cardiac markers

Surface plasmon resonance aided electrochemical immunosensor for CK-MB determination in undiluted serum samples

This article presents a simple chronoamperometric immunosensor for the quantitative assessment of creatine kinase MB (CK-MB) in 50 microL undiluted serum samples. The immunosensor consists of gold working and counter electrodes patterned onto a glass chip by thin-film photolithography and an external Ag|AgCl reference electrode. The detection limit (DL) of the chronoamperometric method is 13 ng mL(-1) (DL = 2xRMSD/S, where RMSD is the residual mean standard deviation of the measured points around a calibration curve with a slope of S). In spiked serum samples, the response was linear up to 300 ng mL(-1) of CK-MB. A surface plasmon resonance (SPR) system with simultaneous electrochemical detection (EC-SPR) aided the development of the sandwich immunoassay. Real-time monitoring of the SPR signal was used to optimize the capture antibody immobilization, CK-MB and detection antibody binding, as well as to minimize the nonspecific adsorption of serum proteins to the sensor surface. The detection antibody has been labeled with alkaline phosphatase (ALP) enzyme for sensitive electrochemical detection. ALP catalyzes the hydrolysis of ascorbic acid phosphate and generates ascorbic acid, which is measured chronoamperometrically. The electrochemical immunoassay for CK-MB was less sensitive to nonspecific adsorption related interferences, had a better detection limit, and required a lower volume of sample than the SPR method.

Plasmonic technology: novel approach to ultrasensitive immunoassays

At the Center for Fluorescence Spectroscopy, we have taken advantage of the favorable properties of surface plasmon-coupled emission (SPCE) to improve fluorescence-based immunoassays. SPCE occurs when excited fluorophores near conducting metallic structures efficiently couple to surface plasmons. These surface plasmons, appearing as free electron oscillations in the metallic layer, produce electromagnetic radiation that preserves the spectral properties of fluorophores but is highly polarized and directional. SPCE immunoassays provide several advantages over other fluorescence-based methods. This review explains new approaches to fluorescence immunoassays, including our own use of SPCE for simultaneous detection of more than one fluorescent marker and performance of immunoassays in the presence of an optically dense medium, such as whole blood.

The increasing impact of laboratory medicine on clinical cardiology

The practice of cardiology continues to evolve along with a better understanding of the pathophysiology of cardiovascular disease and the development of new therapeutic procedures. Consequently, new demands are being made on the in vitro diagnostics industry to improve the performance of existing cardiac markers and to develop novel markers for new cardiac disease indications. Indeed, in the last 20 years there has been a progressive increase in new laboratory tests for markers of cardiac diseases. Several highly sensitive and/or specific assays for the detection of myocardial ischemic damage as well as some immunoassays for cardiac natriuretic hormones, now considered a reliable marker of myocardial function, have become commercially available. In parallel, a growing number of some novel risk factors, which can be assessed and monitored by laboratory methods, have been added to the classical risk factors for cardiovascular disease. Finally, the recent explosion of genetic analysis may soon place at the clinical cardiologist's disposal many laboratory tests for defining the diagnosis at the molecular level, assessing new risk factors, and better targeting the pharmaceutical approaches in patients with cardiovascular disease. In the present article, after a brief description of the analytical tests included in these four groups, each group's impact on clinical cardiology is discussed in detail.

Analytical Evaluation of an Automated Immunoassay for Cardiac Troponin I: The Vidas Troponin I Assay

Cardiac troponin I (cTnI) is a sensitive and specific biochemical marker of myocardial damage. We assessed the analytical performance of the Vidas Troponin I assay (Biomerieux). Controls and serum pools were used to determine the precision, analytical sensitivity and linearity; 97.5 and 99.5 percentiles concentrations were determined from the reference population. Fifty corresponding samples of serum and plasma (lithium-heparin) were tested and the results compared. The in vitro stability of serum and plasma samples was assessed at 20 degrees C, 4 degrees C and -20 degrees C, respectively. Samples of serum were used to assess the agreement between the Vidas Troponin I method and the revised Dimension RxL cTnI method (Dade-Behring). The total imprecision (CVs) was 13.1-5.2% for concentrations ranging between 0.25 and 19.8 microg/l cTnI. The lower detection limit was <0.1 microg/l. The upper reference limit (97.5 and 99.5 percentiles) was 0.11 microg/l and 0.12 microg/l, respectively (CV > 10%). The assay was linear up to 21 microg/l. The concentrations in lithium-heparin plasma were higher compared to those of the matched serum samples. The study of the agreement between the Vidas and Dimension RxL cTnI assays showed a total concordance of 96% with a bias value of -0.042. The Vidas Troponin I test is a fast, precise and sensitive method for the determination of cTnI.

The measurement of cardiac markers: where should we focus?

Cardiac markers are presently a hot topic, with active debate on their use. They now have a major role for cost-effective management of acute chest pain and suspected acute coronary syndrome. The laboratory has a pivotal role in proper selection and interpretation of available markers, depending on the creation of evidence-based knowledge about test utilization and sources of variation. This article reviews this knowledge in the field of biomarkers determination and summarizes the major analytic and clinical issues, with reference to various recent recommendations of laboratory medicine and cardiology expert groups.

Determination of myoglobin: comparative evaluation of the new automated VIDAS assay with two other immunoassays

OBJECTIVES

Myoglobin provides the earliest indication of acute myocardial infarction. In this study, the new myoglobin assay for the VIDAS system (bioMérieux) was evaluated.

DESIGN AND METHODS

This assay, using an enzyme-linked fluorescent immunoassay (ELFIA) method, was compared with the Olympus immunoturbidimetric method and with another immunometric method (Immulite turbo) using an enzyme-linked chemiluminescent immunoassay (CLIA).

RESULTS

The CVs for within-and between-run reproducibility are very similar for the tested methods and acceptable linearity ranges were obtained. No significant interference of hemolysis, turbidity and icteria was observed. In the whole cohort, we obtained decreased values over the entire range of the assay with VIDAS and Immulite turbo methods compared to the Olympus assay; this is probably mainly linked to differences in standards used due to the absence of international standardization of the myoglobin determination.

CONCLUSIONS

The new VIDAS myoglobin automated assay provides biologists with a rapid, accurate and reliable determination of myoglobin in plasma samples collected during cardiac workup.