Evaluation of the light-initiated chemiluminescence assay for quantification of Humulus scandens pollen - specific IgE

AIM

The purpose of this study is to establish a light-initiated chemiluminescence assay (LiCA) for the quantitative analysis of Humulus scandens pollen-specific IgE (sIgE) antibodies.

METHODS

The best chemibeads coupling method in detecting Humulus scandens pollen - sIgE was selected. The working concentrations of the antigen-antibody and the reaction buffer were optimized as components of the reaction system. Then the assay performance was evaluated and the results of LiCA were compared with ImmunoCAP methods.

RESULTS

In the range of 0.23 kUA/L to 100.51 kUA/L, LiCA demonstrated good linearity. The coefficients of variation for repeatability and intermediate precision ranged from 5.96% to 8.58% and 7.53% to 11.25%, respectively. The limit of blank (LoB), limit of detection (LoD), and limit of quantitation (LoQ) were determined to be 0.044 kUA/L, 0.086 kUA/L, and 0.11 kUA/L, respectively. Furthermore, LiCA exhibited a statistically significant correlation with ImmunoCAP (r = 0.990).

CONCLUSION

The established LiCA-based quantitative detection method for Humulus scandens pollen-slgE has good analytical performance and potential clinical application prospects.

Green synthesis as a simple and rapid route to protein modified magnetic nanoparticles for use in the development of a fluorometric molecularly imprinted polymer-based assay for detection of myoglobin

We have developed a low-cost molecularly imprinted polymer (MIP)-based fluorometric assay to directly quantify myoglobin in a biological sample. The assay uses a previously unreported method for the development of microwave-assisted rapid synthesis of aldehyde functionalized magnetic nanoparticles, in just 20 min. The aldehyde functionalized nanoparticles have an average size of 7.5 nm ± 1.8 and saturation magnetizations of 31.8 emu g-1 with near-closed magnetization loops, confirming their superparamagnetic properties. We have subsequently shown that protein tethering was possible to the aldehyde particles, with 0.25 ± 0.013 mg of myoglobin adsorbed to 20 mg of the nanomaterial. Myoglobin-specific fluorescently tagged MIP (F-MIP) particles were synthesized and used within the assay to capture myoglobin from a test sample. Excess F-MIP was removed from the sample using protein functionalized magnetic nanoparticles (Mb-SPION), with the remaining sample analyzed using fluorescence spectroscopy. The obtained calibration plot of myoglobin showed a linear correlation ranging from 60 pg ml-1 to 6 mg ml-1 with the limit of detection of 60 pg ml-1. This method was successfully used to detect myoglobin in spiked fetal calf serum, with a recovery rate of more than 93%.

Cardiovascular disease testing on the Dimension Vista system: biomarkers of acute coronary syndromes

OBJECTIVES

Performance characteristics of the LOCI cTnI, CK-MB, MYO, NTproBNP and hsCRP methods on the Dimension Vista System were evaluated.

DESIGN AND METHODS

Imprecision (following CLSI EP05-A2 guidelines), limit of quantitation (cTnI), limit of blank, linearity on dilution, serum versus plasma matrix studies (cTnI), and method comparison studies were conducted.

RESULTS

Method imprecision of 1.8 to 9.7% (cTnI), 1.8 to 5.7% (CK-MB), 2.1 to 2.2% (MYO), 1.6 to 3.3% (NTproBNP), and 3.5 to 4.2% (hsCRP) were demonstrated. The manufacturer's claimed imprecision, detection limits and upper measurement limits were met. Limit of Quantitation was 0.040 ng/mL for the cTnI assay. Agreement of serum and plasma values for cTnI (r=0.99) was shown. Method comparison study results were acceptable.

CONCLUSIONS

The Dimension Vista cTnI, CK-MB, MYO, NTproBNP, and hsCRP methods demonstrate acceptable performance characteristics for use as an aid in the diagnosis and risk assessment of patients presenting with suspected acute coronary syndromes.

Absolute myoglobin quantitation in serum by combining two-dimensional liquid chromatography-electrospray ionization mass spectrometry and novel data analysis algorithms

To measure myoglobin, a marker for myocardial infarction, directly in human serum, two-dimensional liquid chromatography in combination with electrospray ionization mass spectrometry was applied as an analytical method. High-abundant serum proteins were depleted by strong anion-exchange chromatography. The myoglobin fraction was digested and injected onto a 60 mm x 0.2 mm i.d. monolithic capillary column for quantitation of selected peptides upon mass spectrometric detection. The addition of known amounts of myoglobin to the serum sample was utilized for calibration, and horse myoglobin was added as an internal standard to improve reproducibility. Calibration graphs were linear and facilitated the reproducible and accurate determination of the myoglobin amount present in serum. Manual data evaluation using integrated peak areas and an automated multistage algorithm fitting two-dimensional models of peptide elution profiles and isotope patterns to the mass spectrometric raw data were compared. When the automated method was applied, a myoglobin concentration of 460 pg/microL serum was determined with a maximum relative deviation from the theoretical value of 10.1% and a maximum relative standard deviation of 13.4%.

False-positive troponin I measured with the Abbott AxSYM attributed to fibrin interference

BACKGROUND

Serum is often used for the measurement of cardiac troponin I (cTnI). Previous reports suggest that fibrin present in serum samples collected for cTnI analysis may interfere with measurement of this marker. We investigated the incidence and magnitude of fibrin interference in serum specimens submitted for cTnI measurement using the AxSYM analyzer by performing duplicate analysis of all specimens with increased cTnI results.

METHODS

Over a 4-month period, we analyzed 3692 specimens for cTnI with the Abbott AxSYM. Of these, 307 (8.3%) showed increased cTnI. A threshold of three times the precision of the method (15%) was used to judge discrepancies between duplicate analyses of specimens; all specimens being recentrifuged between the initial and repeat cTnI analyses.

RESULTS

Of 307 patient specimens with elevated cTnI concentrations, 24 (7.8%) demonstrated differences of greater than 45% between duplicate analyses. Concentrations of cTnI obtained on initial analysis of these 24 specimens ranged from 2.4 to 24.0 microg/l. Repeat analysis showed the repeat values for 20 (83%) to be within the normal reference interval, with 16 (67%) showing concentrations of less than 0.3 microg/l.

CONCLUSIONS

Our finding indicates that interference should be highly suspected in serum specimens where the initially measured cTnI concentrations is in the range of 2.0-25.0 microg/l when using the Abbott AxSYM. The finding of no interference in specimens with measured troponin concentration greater than 25.0 microg/l suggests that the interference effect of fibrin is generally not sufficient to cause spurious elevations of cTnI into this range. In addition, since switching to plasma as the specimen of choice for the AxSYM, we have not observed any discrepant cTnI results following duplicate analysis of over 200 patient samples with initial measured cTnI concentrations of 2.0 microg/l or greater.

Evaluation of the Stratus CS fluorometer for the determination of plasma myoglobin

Circulating myoglobin is recognized as an early and sensitive marker of acute coronary diseases. Long turnaround time of myoglobin assays jeopardize their clinical utility. We evaluated the analytical performance of the Stratus CS fluorometric enzyme immunoassay based on dendrimer technology, and claimed to achieve a fast and reliable determination of plasma myoglobin concentrations. Precision complied with the recommended analytical performance criteria. Method comparison and recovery experiments indicated, that despite good between-method correlations, the Stratus CS method overestimated myoglobin concentrations in comparison with values obtained on Cobas Integra 400 and BN A. However, since the manufacturers' cut-off for elevated plasma myoglobin levels was higher for Stratus CS than for other techniques, few discrepant results were observed between methods. Elevated levels of hemoglobin, triglycerides and rheumatoid factors did not interfere in the Stratus CS method but hyperbilirubinemia caused a positive difference.

Myoglobin immunoassay utilizing directional surface plasmon-coupled emission

We described an immunoassay for the cardiac marker myoglobin on a thin silver mirror surface using surface plasmon-coupled emission (SPCE). SPCE occurs for fluorophores in proximity (within approximately 200 nm) of a thin metal film (in our case, silver) and results in a highly directional radiation through a glass substrate at a well-defined angle from the normal axis. We used the effect of SPCE to develop a myoglobin immunoassay on the silver mirror surface deposited on a glass substrate. Binding of the labeled anti-myoglobin antibodies led to the enhanced fluorescence emission at a specific angle of 72 degrees . The directional and enhanced directional fluorescence emission enables detection of myoglobin over a wide range of concentrations from subnormal to the elevated level of this cardiac marker. Utilizing SPCE allowed us also to demonstrate significant background suppression (from serum or whole blood) in the myoglobin immunoassay. We expect SPCE to become a powerful technique for performing immunoassays for many biomarkers in surface-bound assays.

Standardization of immunoassays for measurement of myoglobin in serum. Phase I: Evaluation of candidate secondary reference materials

BACKGROUND

Myoglobin is a low-molecular weight protein present in the cytosol of striated muscles. Its concentrations in serum can be measured by immunoassays and are used as an early indicator of myocardial necrosis. Since variability among commercial myoglobin assays exists, standardization of myoglobin assays is needed.

METHODS

An international collaborative study was organized with the involvement of seven companies using 12 different automated platforms for measuring myoglobin. Five candidate secondary, i.e., matrixed, reference materials were assayed in relation to linearity, imprecision, recovery rate and commutability to demonstrate a possible identity between the materials and the usual routine serum samples.

RESULTS

One lyophilized candidate material (human heart myoglobin in human serum) was selected as the most suitable secondary reference material, based on the criteria examined. Used as a calibrator a posteriori, the bias between the various myoglobin assays for a frozen human serum pool was reduced from 32% to 13%.

CONCLUSION

This study provides the basis for the selection of an internationally recognized secondary reference material.

The influence of hemolysis, turbidity and icterus on the measurements of CK-MB, troponin I and myoglobin

To decide on the acceptability of a specimen for the measurement of serum CK-MB, troponin I and myoglobin, we investigated the influence of hemolysis, turbidity, and icterus on those tests by adding arbitrarily made interferents. A total of 16 cases each for CK-MB and troponin I, and 18 cases for myoglobin tests were studied to verify the effects of hemolysis, turbidity, and unconjugated hyperbilirubinemia. A total of 16 cases were studied to clarify the effects of the conjugated hyperbilirubinemia. We graded the severity of hemolysis, turbidity, and icterus as mild, moderate, and severe after adding hemolysate, Intralipos (20% soybean oil), and unconjugated or conjugated bilirubin to sera. ACS180SE automated chemiluminescence system was used to measure CK-MB, troponin I, and myoglobin. CK-MB and troponin I were affected by any degree of hemolysis, turbidity, unconjugated hyperbilirubinemia, and conjugated hyperbilirubinemia, while myoglobin was affected only by severe unconjugated hyperbilirubinemia and conjugated hyperbilirubinemia in the samples with concentration higher than reference range, resulting in concentration level lower than baseline. In conclusion, the results of cardiac markers should be carefully interpreted when the specimens are hemolyzed, turbid or icteric.

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.

Cardiac troponin and beta-type myosin heavy chain concentrations in patients with polymyositis or dermatomyositis

Cardiac troponin T (cTnT), cardiac troponin I (cTnI), myosin heavy chains (MHC), myoglobin, creatine kinase (CK), and creatine kinase isoenzyme MB (CKMB), were measured in blood samples from 39 polymyositis (PM) or dermatomyositis (DM) patients without clinical evidence for cardiac involvement to evaluate their clinical usefulness in this patient population. MHC, myoglobin, and CKMB were frequently elevated and correlated with each other and with disease severity. Undetectable cTnI in all but one patient indicated that MHC was released from skeletal muscle, thereby providing the first laboratory evidence of frequent slow-twitch muscle fibre-necrosis in patients with PM or DM. CKMB was elevated in 51%, cTnT in 41%, and cTnI in only 2.5% of patients. cTnI did not correlate with other markers or with disease severity scores. The close correlations found between cTnT and skeletal muscle damage markers and the relationship between cTnT with disease severity without clinical evidence for myocardial damage suggest a release of cTnT from skeletal muscle. The relationship of cTnT with disease severity indicates a possible role of the marker for risk stratification. However, the prognostic values of cardiac troponins and other muscle damage markers in PM/DM patients remain to be compared in prospective outcome trials.