Enhancing the understanding of SARS-CoV-2 protein with structure and detection methods: An integrative review

As the rapid and accurate screening of infectious diseases can provide meaningful information for outbreak prevention and control, as well as owing to the existing limitations of the polymerase chain reaction (PCR), it is imperative to have new and validated detection techniques for SARS-CoV-2. Therefore, the rationale for outlining the techniques used to detect SARS-CoV-2 proteins and performing a comprehensive comparison to serve as a practical benchmark for future identification of similar viral proteins is clear. This review highlights the urgent need to strengthen pandemic preparedness by emphasizing the importance of integrated measures. These include improved tools for pathogen characterization, optimized societal precautions, the establishment of early warning systems, and the deployment of highly sensitive diagnostics for effective surveillance, triage, and resource management. Additionally, with an improved understanding of the virus' protein structure, considerable advances in targeted detection, treatment, and prevention strategies are expected to greatly improve our ability to respond to future outbreaks.

Development of an ID-LC-MS/MS method using targeted proteomics for quantifying cardiac troponin I in human serum

BACKGROUND

Cardiac troponin is a complex protein consisting of the three subunits I, T and C located in heart muscle cells. When the heart muscle is damaged, it is released into the blood and can be detected. Cardiac troponin I (cTnI) is considered the most reliable and widely accepted test for detecting and confirming acute myocardial infarction. However, there is no current standardization between the commercial assays for cTnI quantification. Our work aims to create a measurement procedure that is traceable to the International System of Units for accurately measuring cardiac cTnI levels in serum samples from patients.

METHODS

The workflow begins with immobilizing anti-cTnI antibodies onto magnetic nanoparticles to form complexes. These complexes are used to isolate cTnI from serum. Next, trypsin is used to enzymatically digest the isolated cTnI. Finally, the measurement of multiple cTnI peptides is done simultaneously using isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS).

RESULTS

The maximum antibody immobilization was achieved by combining 1 mg of nanoparticles with 100 μg of antibody, resulting in an average of 59.2 ± 5.7 μg/mg of immobilized antibody. Subsequently, the anti-cTnI-magnetic nanoparticle complex was utilized to develop and validate a method for quantifying cTnI in human serum using ID-LC-MS/MS and a protein calibration approach. The analytical method was assessed regarding linearity and recovery. The developed method enables the quantification of cTnI from 0.7 to 24 μg/L (R > 0.996). The limit of quantification was 1.8 μg/L and the limit of detection was 0.6 μg/L. Intermediate precision was ≤ 9.6% and repeatability was 2.0-8.7% for all quality control materials. The accuracy of the analyzed quality control materials was between 90 and 110%. Total measurement uncertainties for target value assignment (n = 6) were found to be ≤ 12.5% for all levels.

CONCLUSIONS

The analytical method demonstrated high analytical performance in accurately quantifying cardiac troponin I levels in human serum. The proposed analytical method has the potential to facilitate the harmonization of cTnI results between clinical laboratories, assign target values to secondary certified reference materials and support reliable measurement of cTnI.

A new method for the evaluation of measurement uncertainty in strict accordance with measurement model: Determination of total thyroxine in human serum by triple isotope dilution mass spectrometry

The rigorous and reasonable evaluation of uncertainty is crucial for the reliability of the results of a reference measurement procedure. A new uncertainty budget is proposed for uncertainty evaluation of a reference measurement procedure for total thyroxine in human serum based on isotope dilution liquid chromatography-mass spectrometry. In this work, a measurement model for uncertainty evaluation of triple isotope dilution-mass spectrometry was established. The propagation of uncertainties assigned to various input quantities was expressed in strict accordance with the measurement model. A detailed description of the uncertainty evaluation process for the measurement result of a specific serum is given, including the estimate of the input quantities and the determination of the combined standard uncertainty. The expanded uncertainty of the specific human serum (at coverage probability of 95%) was 4.8 nmol/L at the concentration level of 113.6 nmol/L.

Quantitation of plasma metanephrines using isotope dilution liquid chromatography tandem mass spectrometry (ID-LC/MS/MS): a candidate reference measurement procedure and its application to evaluating routine ID-LC/MS/MS methods

Accurate measurement of plasma metanephrines (MNs) including metanephrine (MN) and normetanephrine (NMN) is crucial for the screening and diagnosis in pheochromocytomas and paragangliomas (PPGLs). Although the number of laboratories using liquid chromatography tandem mass spectrometry (LC-MS/MS) method to measure MNs has been increasing rapidly, those laboratory-developed assays showed incomparable results. There are no reference measurement procedures (RMPs) or reference materials (RMs) for MNs in Joint Committee for Traceability in Laboratory Medicine (JCTLM), which hindered the standardization of MNs measurement. We established a candidate RMP (cRMP) based on isotope dilution liquid chromatography tandem mass spectrometry (ID-LC/MS/MS) method for plasma MNs measurement. Plasma samples were spiked with MN-D3 and NMN-D3 as internal standards; protein precipitation and ion-exchange solid phase extraction (SPE) were performed to extract samples, eventually analyzed by LC-MS/MS. The cRMP was applied to evaluate two routine ID-LC/MS/MS methods through split-sample comparisons. Fifty-three individual patient samples were determined by cRMP and two routine ID-LC/MS/MS methods; results were analyzed by ordinary linear regression and Bland-Altman plots. The cRMP exhibited desirable imprecision, with intra-run and total imprecision (coefficient variation, CV) for MN being 0.79-1.36% and 1.53-1.87% and for NMN being 1.10-1.34% and 1.15-1.64%. The analytical recoveries of MN and NMN ranged from 98.3 to 101.7% and from 98.5 to 101.9%, respectively. Significant calibrator biases and sample-specific deviations were observed in method comparison. An accurate, precise, and reliable cRMP for plasma MNs was developed, and RMs with value assigned following the cRMP would help minimize the calibration bias and improve the comparability of different measuring systems.

Candidate reference measurement procedure based on HPAEC-PAD for the development of certified reference materials for monosaccharides in serum

To achieve the measurement reliability of monosaccharides used as diagnostic markers in clinical fields, it is essential to establish certified reference materials (CRMs). The purpose of this study is to develop a serum CRM by adopting high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) as a new candidate reference measurement procedure for the measurement of glucose and galactose, common diagnostic markers of diabetes and galactosemia, respectively. Using various monosaccharides as internal standards, the accuracy of the HPAEC-PAD method was tested by measuring glucose CRM following treatment with three different deproteinization methods: ultrafiltration, protein precipitation by trichloroacetic acid (TCA), and protein precipitation by acetonitrile. Results showed that ultrafiltration and 5% TCA provided good accuracy with every tested monosaccharide as the internal standard. Accordingly, serum samples in this study were treated by ultrafiltration after adding 2-deoxy-D-glucose and arabinose, which were selected as internal standards for galactose and glucose, respectively. Both intra- and inter-day recovery tests showed good precision and accuracy within 2%. From the serum CRM batches prepared at two levels, 11 units were analyzed by exact-matched calibration methods, and the mass fractions of galactose and glucose were determined via HPAEC-PAD. The between-unit relative standard deviations were not more than 1.5%, showing homogeneity. The expanded uncertainties (%) of galactose and glucose for both levels were less than 3.6% and 2.3% at 95% confidence. The HPAEC-PAD method presented in this study can significantly improve the accuracy and precision of simultaneous monosaccharide analysis, allowing for the development of further serum CRMs for monosaccharides. Graphical abstract.

An isotope dilution liquid chromatography-tandem mass spectrometry candidate reference measurement procedure for aldosterone measurement in human plasma

Accurate quantitation of aldosterone is clinically important in standardized testing for primary aldosteronism. The results are often variable when performed by clinical immunoassays. To standardize and ensure the accuracy of clinical systems, reference measurement procedures (RMPs) with higher metrological order are required. A simple and reliable isotope dilution LC-IDMS/MS-based measurement procedure for human plasma aldosterone has been developed. This method involved plasma spiked with a deuterium-labelled internal standard, equilibrated for 0.5 h, and extracted by liquid-liquid extraction (LLE) without derivatization. Aldosterone and its structural analogues were baseline separated with a C18-packed UHPLC column with gradient elution within 7 min. The signal intensity variability and measurement imprecision were reduced by bracketing calibration during plasma aldosterone value assignment. The limit of detection (LoD) was 19.4 pmol/L with a signal-to-noise ratio (S/N) > 3. The lowest limit of quantification (LLoQ) was 27.7 pmol/L (S/N > 10 and CV < 10.0%). LLE was performed with 1 mL of n-hexane/ethyl acetate (3:2, v/v), and the extraction recovery was determined to be 92.15 ± 3.54%. The imprecisions were ≤ 3.18% for samples at 124.8, 867.0, and 2628.5 pmol/L. The recoveries were 98.11-101.61%. The relative bias between this candidate RMP and the established RMP was 2.76-1.89%. The linearity response ranged from 27.7 to 2774.4 pmol/L with R² = 0.999. The method performance met the requirements of RMPs (≤ 5% total CV and ≤ 3% bias). Furthermore, the developed method was applied to evaluate immunoassays through 41 patient sample comparisons. The calibration and measurement capability (CMC) of this method were also evaluated by measuring these samples. The candidate RMP can serve as an accurate reference baseline for routine methods and can be used for value assignment for reference materials. Selected ion chromatograms by LC-MS/MS using a C18 column for aldosterone and its structural analogues.

The performance of human cytomegalovirus digital PCR reference measurement procedure in seven external quality assessment schemes over four years

A candidate digital PCR (dPCR)-based reference measurement procedure for quantification of human cytomegalovirus (hCMV) was evaluated in 10 viral load comparison schemes (seven external quality assessment (EQA) and three additional training schemes) organized by INSTAND e.V. over four years (between September 2014 and March 2018). Four metrology institutes participated in these schemes using the same extraction method and dPCR measurement procedure for the hCMV specific target sequence of UL54 gene. The calibration independent reference measurement procedure results from the metrology institutes were compared to the results of the clinical diagnostic laboratories applying hCMV qPCR measurement procedures calibrated to reference materials. While the criteria for the acceptable deviation from the target value interval for INSTAND's EQA schemes is from -0.8 log₁₀ to +0.8 log₁₀, the majority of dPCR results were between -0.2 log₁₀ to +0.2 log₁₀. Only 4 out of 45 results exceeded this interval with the maximum deviation of -0.542 log₁₀. In the training schemes containing samples with lower hCMV concentrations, more than half of the results deviated less than ±0.2 log₁₀ from the target value, while more than 95% deviated less than ±0.4 log₁₀ from the target value. Evaluation of intra- and inter-laboratory variation of dPCR results confirmed high reproducibility and trueness of the method. This work demonstrates that dPCR has the potential to act as a calibration independent reference measurement procedure for the value assignment of hCMV calibration and reference materials to support qPCR calibration as well as ultimately for routine hCMV load testing.

A roadmap for the standardization of hemoglobin A2

BACKGROUND

Standardization of laboratory tests can be a long process, and this is the case with regards to the methods used to measure hemoglobin A₂ (HbA₂), an important marker for beta-thalassemia and other thalassemic conditions. The IFCC standardization project started in 2004, and it took at least 15 years before developing a reference measurement procedure, defining and producing calibrators and certified reference materials.

METHODS

A series of steps have to be undertaken in order to promote the standardization in the field, a process involving a number of stakeholders (manufacturers, scientific societies, national health bodies, laboratory professionals, clinicians). In this work we describe some possible process indicators, in order to assure that the standardization will have internal and external validity and be effective for a long time. These indicators concern the inter-method studies, elaboration of External Quality Assessment Schemes, and the evaluation of the yearly distributions of HbA₂ measurements collected in selected laboratories.

RESULTS

Preliminary results are reported concerning the yearly distributions of HbA₂, collected in two different locations, and using different analytical methods. Median yearly values were found very constant over the years, but different between methods. On the other side, results obtained on the same specimens using two different techniques, proved that results by capillary electrophoresis in 2 out of the 3 years of observation, were significantly lower than those by HPLC.

CONCLUSION

In this document we report what has been done so far, and what has to be done to achieve the standardization of the measurement of HbA₂ worldwide.

An isotope dilution LC-MS/MS based candidate reference method for the quantification of cyclosporine A, tacrolimus, sirolimus and everolimus in human whole blood

An isotope dilution LC-MS/MS based candidate reference measurement procedure for the quantification of cyclosporine A, tacrolimus, sirolimus and everolimus in human whole blood is presented to be used for evaluation and standardization of routine assays applied for therapeutic drug monitoring. The assay allows baseline separation of the four immunosuppressive drugs within a total runtime of 9 minutes using a C4 reversed phase column. Sample preparation is based on protein precipitation with zinc sulphate followed by purification with solid phase extraction. Reference materials used in this reference measurement procedure were characterized by qNMR and an absolute content of analytes calculated to guarantee traceability to SI units. As internal standards the corresponding deuterated and ¹³C-labelled analytes were used. The method allows the measurement of cyclosporine A in the range of 5 ng/mL to 2100 ng/mL; tacrolimus, sirolimus and everolimus were analysed in the range of 0.25 ng/mL to 50 ng/mL. Imprecision for inter-day measurements were found to be ≤3.5% for cyclosporine A and ≤4.4% for tacrolimus, sirolimus and everolimus. Accuracy was found to be within 101% and 108% for cyclosporine A and between 95% and 104% for the macrolide compounds. The uncertainty was evaluated according to the GUM. Expanded measurement uncertainties were found to be ≤7.2% for cyclosporine A, ≤6.8% for tacrolimus, ≤9.0% for sirolimus and ≤8.9% for everolimus (k = 2).

Quality specifications and their daily application to evaluate the accuracy of reference measurements for serum concentrations of 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2

BACKGROUND

Reference measurement procedures (RMP) have rigorous accuracy specifications. For total 25-hydroxyvitamin D, 25(OH)D, bias ≤1.7% and CV ≤5% are recommended. These quality specifications are impractical for minor analytes, such as 25(OH)D₂. Furthermore, documentation on RMP quality performance specifications for the individual 25(OH)D metabolites and their daily application are missing.

METHODS

To assess accuracy, we used zeta-scores. Daily, 5-10 specimens (duplicate) and 3 reference materials (singleton or duplicate) were measured for 25(OH)D₃ and 25(OH)D₂ using JCTLM-accepted LC-MS/MS RMPs. Protocols were repeated on 3-4 occasions to generate campaign results. We used separate zeta-score acceptability criteria for daily (≤|2|) and campaign (≤|1|) evaluations. Allowable imprecision was determined experimentally.

RESULTS

Across 7 campaigns, unacceptable daily zeta-scores required repeating 2 runs for 25(OH)D₃ and 5 runs for 25(OH)D₂. Hence, the zeta-scores of acceptable reference material results indicated high accuracy. The allowable imprecision for the RMPs was ≤5% (daily) and ≤ 3% (campaign) for 25(OH)D₃ and ≤ 7% (daily) and ≤ 4% (campaign) for 25(OH)D₂, respectively.

CONCLUSIONS

Using zeta-scores and experimentally derived imprecision, we developed a straightforward approach to assess the acceptability of individual 25(OH)D reference measurements, providing also much-needed practical accuracy specifications for 25(OH)D₂.