Evaluation of imprecision in the different detection methods of Zn based on 5 years of data from an external quality assessment program in China.

BACKGROUND: This study examines the imprecision of zinc (Zn) measurements across various clinical detection methods by analyzing the external quality assessment (EQA) data from 2018 to 2022. The findings of this study aim to offer recommendations for enhancing Zn measurements. METHODS: Participating laboratories were grouped into peer categories based on the detection methods. The robust mean and coefficient of variation (CV) of the samples were calculated following ISO 13528 guidelines. The evaluation criteria for optimal, desirable, and minimum allowable imprecision in Zn estimation are 2.50%, 5.05%, and 7.55%, respectively, based on biological variation. Furthermore, the study examined inter-lab CVs, inter-method bias, and the passing rate. The impact of sample concentration on CVs and the pass rate was also investigated. RESULTS: Over the past five years, 4283 laboratories participated in the EQA program, showing a high pass rate that improved as sample concentration increased. Differential pulse polarography (DPP) demonstrated stable and low CVs (0.61-1.86%). Although differential pulse stripping (DPS) was less stable than DPP, it still exhibited a low CV (0.71-3.10%). Graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic absorption spectrometry (FAAS) performed similarly and displayed stable CVs (2.39-4.42%) within the acceptable range of desirable imprecision (5.05%). However, the CVs for ICP-MS were unacceptable in three out of the five years (5.28-6.20%). In 2022, the number of participating laboratories for DDP, DPS, GFAAS, FAAS and ICP-MS is 131, 35, 35, 820 and 72, respectively. CONCLUSION: This study provides reliable insights into the imprecision of Zn measurements in clinical laboratories. The findings indicate that additional efforts are required to reduce the imprecision of ICP-MS in Zn measurements.

Insight into the status of plasma renin and aldosterone measurement: findings from 526 clinical laboratories in China.

OBJECTIVES: Accurate measurements of renin and aldosterone levels play an important role in primary aldosteronism screening, which is of great importance in the management and categorization of hypertension. The objective of this study is to investigate the current status of plasma renin and aldosterone measurements in China, which is achieved by analyzing the results of 526 clinical laboratories nationwide for three pooled fresh plasma samples derived from more than 2,000 patients. METHODS: Renin and aldosterone in three pooled plasma samples were measured four times in 526 laboratories employing various measurement systems. The inter- and intra-laboratory %CV were calculated and compared. To determine the source of the substantial inter-laboratory %CV, laboratories were categorized according to the measurement systems they are using, and both the inter- and intra-measurement-system %CV were calculated and compared. RESULTS: Regarding renin, the majority of laboratories use four primary commercial immunoassays. However, for aldosterone, in addition to commercial immunoassays, laboratory-developed liquid chromatography-tandem mass spectrometry (LC-MS) methods are also used by laboratories. The median values of intra-laboratory %CVs, intra-measurement-system %CVs, inter-laboratory %CVs, and inter-measurement systems %CVs varied between 1.6 and 2.6 %, 4.6 and 14.9 %, 8.3 and 25.7 %, and 10.0 and 34.4 % for renin, respectively. For aldosterone, these values ranged from 1.4 to 2.2 %, 2.5-14.7 %, 9.9-31.0 %, and 10.0-35.5 %, respectively. CONCLUSIONS: The precision within laboratories and measurement systems for plasma renin and aldosterone measurements is satisfactory. However, the comparability between laboratories using different measurement systems remains lacking, indicating the long way to achieve standardization and harmonization for these two analytes.

Altered neopterin and IDO in kynurenine metabolism based on LC-MS/MS metabolomics study: Novel therapeutic checkpoints for type 2 diabetes mellitus.

BACKGROUND: This study assessed the alternations of kynurenine pathway (KP) and neopterin in type 2 diabetes mellitus (T2DM) and explored possible differential metabolites. METHODS: A fresh residual sera panel was collected from 80 healthy control (HC) individuals and 72 T2DM patients. Metabolites/ratios of interest including tryptophan (TRP), kynurenine (KYN), 5-hydroxytryptamine (5HT), kynurenic acid (KA), xanthurenic acid (XA), neopterin (NEO), KA/KYN ratio and KYN/TRP ratio were determined using a targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) metabolomics approach, and the difference between groups was assessed. Supervised orthogonal partial least squares-discriminant analysis and differential metabolite screening with fold change (FC) were performed to identify distinct biomarkers. The diagnostic performance of KP metabolites in T2DM was evaluated. RESULTS: Significant decreases of TRP, 5HT, KA, XA, and KA/KYN and increases of KYN/TRP and NEO in T2DM compared to HC group were observed (P < 0.05). The KP metabolites panel significantly changed between T2DM and HC groups (Q2: 0.925, P < 0.005). 5HT (FC: 0.63, P < 0.01) and NEO (FC: 3.27, P < 0.01) were proven to be distinct differential metabolites. A combined testing of fasting plasma glucose and KYN/TRP showed good value in the prediction of T2DM (AUC: 0.904, 95% CI 0.843-0.947). CONCLUSIONS: The targeted LC-MS/MS metabolomics study is a powerful tool for evaluating the status of T2DM. This study facilitated the application of KP metabolomics into future clinical practice. 5HT and NEO are promising biomarkers in T2DM. KYN/TRP was highly associated with the development of T2DM and may serve as a potential treatment target.

Investigating the Current Harmonization Status of Tumor Markers Using Global External Quality Assessment Programs: A Feasibility Study.

BACKGROUND: The harmonization status of most tumor markers (TMs) is unknown. We report a feasibility study performed to determine whether external quality assessment (EQA) programs can be used to obtain insights into the current harmonization status of the tumor markers α-fetoprotein (AFP), prostate specific antigen (PSA), carcinoembryonic antigen (CEA), cancer antigen (CA)125, CA15-3 and CA19-9. METHODS: EQA sample results provided by 6 EQA providers (INSTAND [Germany], Korean Association of External Quality Assessment Service [KEQAS, South Korea], National Center for Clinical Laboratories [NCCL, China], United Kingdom National External Quality Assessment Service [UK NEQAS, United Kingdom], Stichting Kwaliteitsbewaking Medische Laboratoriumdiagnostiek [SKML, the Netherlands], and the Royal College of Pathologists of Australasia Quality Assurance Programs [RCPAQAP, Australia]) between 2020 and 2021 were used. The consensus means, calculated from the measurement procedures present in all EQA programs (Abbott Alinity, Beckman Coulter DxI, Roche Cobas, and Siemens Atellica), was used as reference values. Per measurement procedure, the relative difference between consensus mean for each EQA sample and the mean of all patient-pool-based EQA samples were calculated and compared to minimum, desirable, and optimal allowable bias criteria based on biological variation. RESULTS: Between 19040 (CA15-3) and 25398 (PSA) individual results and 56 (PSA) to 76 (AFP) unique EQA samples were included in the final analysis. The mean differences with the consensus mean of patient-pool-based EQA samples for all measurement procedures were within the optimum bias criterion for AFP, the desirable bias for PSA, and the minimum bias criterion for CEA. However, CEA results <8 µg/L exceeded the minimum bias criterion. For CA125, CA15-3, and CA19-9, the harmonization status was outside the minimum bias criterion, with systematic differences identified. CONCLUSIONS: This study provides relevant information about the current harmonization status of 6 tumor markers. A pilot harmonization investigation for CEA, CA125, CA15-3, and CA19-9 would be desirable.

An LC-MS/MS method for serum cystatin C quantification and its comparison with two commercial immunoassays.

OBJECTIVES: The standardization of cystatin C (CysC) measurement has received increasing attention in recent years due to its importance in estimating glomerular filtration rate (GFR). Mass spectrometry-based assays have the potential to provide an accuracy base for CysC measurement. However, a precise, accurate and sustainable LC-MS/MS method for CysC is still lacking. METHODS: The developed LC-MS/MS method quantified CysC by detecting signature peptide (T3) obtained from tryptic digestion. Stable isotope labeled T3 peptide (SIL-T3) was spiked to control matrix effects and errors caused by liquid handling. The protein denaturation, reduction and alkylation procedures were combined into a single step with incubation time of 1 h, and the digestion lasted for 3.5 h. In the method validation, digestion time-course, imprecision, accuracy, matrix effect, interference, limit of quantification (LOQ), carryover, linearity, and the comparability to two routine immunoassays were evaluated. RESULTS: No significant matrix effect or interference was observed with the CysC measurement. The LOQ was 0.21 mg/L; the within-run and total imprecision were 1.33-2.05 % and 2.18-3.90 % for three serum pools (1.18-5.34 mg/L). The LC-MS/MS method was calibrated by ERM-DA471/IFCC and showed good correlation with two immunoassays traceable to ERM-DA471/IFCC. However, significant bias was observed for immunoassays against the LC-MS/MS method. CONCLUSIONS: The developed LC-MS/MS method is robust and simpler and holds the promise to provide an accuracy base for routine immunoassays, which will promote the standardization of CysC measurement.

The Role of IL-6 in Neurodegenerative Disorders.

"Neurodegenerative disorder" is an umbrella term for a group of fatal progressive neurological illnesses characterized by neuronal loss and inflammation. Interleukin-6 (IL-6), a pleiotropic cytokine, significantly affects the activities of nerve cells and plays a pivotal role in neuroinflammation. Furthermore, as high levels of IL-6 have been frequently observed in association with several neurodegenerative disorders, it may potentially be used as a biomarker for the progression and prognosis of these diseases. This review summarizes the production and function of IL-6 as well as its downstream signaling pathways. Moreover, we make a comprehensive review on the roles of IL-6 in neurodegenerative disorders and its potential clinical application.

Evaluation of Coefficients of Variation for Clinical Chemistry Tests Based on Internal Quality Control Data Across 5,425 Laboratories in China From 2013 to 2022.

Background: Clinical chemistry tests are most widely used in clinical laboratories, and diverse measurement systems for these analyses are available in China. We evaluated the imprecision of clinical chemistry measurement systems based on internal QC (IQC) data. Methods: IQC data for 27 general chemistry analytes were collected in February each year from 2013 to 2022. Four performance specifications were used to calculate pass rates for CVs of IQC data in 2022. Boxplots were drawn to analyze trends of CVs, and differences in CVs among different groups were assessed using the Mann-Whitney U-test or Kruskal-Wallis test. Results: The number of participating laboratories increased significantly from 1,777 in 2013 to 5,425 in 2022. CVs significantly decreased for all 27 analytes, except creatine kinase and lipase. Triglycerides, total bilirubin, direct bilirubin, iron, and γ-glutamyl transferase achieved pass rates >80% for all goals. Nine analytes with pass rates <80% based on 1/3 allowable total error were further analyzed; the results indicated that closed systems exhibited lower CVs than open systems for all analytes, except total protein. For all nine analytes, differences were significant between tertiary hospitals and non-tertiary hospitals and between accredited and non-accredited laboratories. Conclusions: The CVs of IQC data for clinical chemistry have seen a continuous overall improvement in China. However, there is ample room for imprecision improvement for several analytes, with stricter performance specifications.

Abnormal kynurenine-pathway metabolites in gout: Biomarkers exploration based on orthogonal partial least squares-discriminant analysis.

BACKGROUND: This study aims to investigate serological characteristics of kynurenine pathway (KP) metabolites in healthy controls (HC) and gout patients and explore possible differential metabolites. METHODS: A total of 191 individual fresh residual sera was collected from 129 HC and 62 gout patients. A liquid chromatography-tandem mass spectrometry method was fully validated to measure 6 metabolites, including tryptophan (TRP), kynurenine (KYN), 5-hydroxytryptamine (5HT), kynurenic acid (KA), xanthurenic acid (XA), and neopterin (NEO). Supervised orthogonal partial least squares-discriminant analysis (OPLS-DA) and differential metabolite screening with fold change (FC) were performed to identify intrinsic variations and differential levels of KP metabolites between the HC and gout groups. Logistic regression was used to assess the contributions of KP metabolites to gout. RESULTS: There were significant decreases of TRP, 5HT, XA, and NEO and increases of KYN, KA, KA/KYN, and KYN/TRP in gout patients compared to the HC group (all p < 0.05). KP metabolites of the gout group showed good discrimination from those of the HC group (Q2: 0.892). Two distinct different metabolites were identified in gout, i.e., XA (FC: 0.56, p < 0.01) and NEO (FC: 0.34, p < 0.01). Of the KP metabolites, KYN was strongly associated with gout (OR: 7.91, p < 0.01). CONCLUSIONS: Abnormal levels of serum KP metabolites were observed in gout. XA and NEO are promising biomarkers that were relevant to the status of gout. The level of KYN could be an attractive checkpoint for the management of gout. Continuous monitoring of KP metabolism in gout provides new opportunities to predict therapeutic efficacy and prognosis.

Regio- and diastereoselective synthesis of diverse spirocyclic indenes by cyclization with indene-dienes as two carbon building blocks.

We report a base-promoted cyclization with indene-dienes as two carbon building blocks toward diverse spirocyclic indene scaffolds including hexacyclic spiroindenes bearing benzo pyran motifs and pentacyclic spiroindenes containing oxindole units in high yields with excellent diastereoselectivities.

The necessity for improving lipid testing reagents: A real world study.

BACKGROUND: We investigated the interference of vitamin C (VitC), glycerol fructose, lipoprotein X (LpX) and lipemia on the analysis of serum lipids. METHODS: Serum were collected from 44 patients with VitC infusion, serum lipid concentrations before and after VitC auto-oxidation were compared. Serum of 31 patients with glycerol fructose infusion were collected, triglycerides (TG) measured by glycerol blanking and non-blanking reagents were compared. Forty-four serum samples suspected to contain LpX were collected, LDL-C measured by reagents from five manufacturers were compared. Lipemia samples were collected, LDL-C measured using five different reagents were compared. The interference rate was considered unacceptable if it was greater than 1/2 total allowable error (TEa). RESULTS: In patients with VitC infusion, the interference rates of TG and total cholesterol (TC) were -59% (-123%, -28%) and -15% (-21%, -11%), respectively. In patients with glycerol fructose infusion, the interference rate of TG was 13% (4%, 113%). LpX interference led to increased LDL-C results for most reagents. Lipemia caused great interference with LDL-C analysis. CONCLUSION: VitC, glycerol fructose, LpX and lipemia significantly interfered with lipid assays. The reagent formulation should be improved to get reliable results.

Characterization of tumor-associated reactive astrocytes in gliomas by single-cell and bulk tumor sequencing.

Objective: Astrocytes constitute approximately 30% of cells in gliomas and play important roles in synapse construction and survival. Recently, JAK/STAT pathway activation associated with a new type of astrocyte was reported. However, the implications of these tumor-associated reactive astrocytes (TARAs) in glioma are not known. Methods: We comprehensively assessed TARAs in gliomas, both in single cells and at the bulk tumor level, by analyzing five independent datasets. First, we analyzed two single-cell RNA sequencing datasets of 35,563 cells from 23 patients to estimate the infiltration level of TARAs in gliomas. Second, we collected clinical information and genomic and transcriptomic data of 1,379 diffuse astrocytoma and glioblastoma samples from the Chinese Glioma Genome Atlas (CGGA) and The Cancer Genome Atlas datasets to evaluate the genomic, transcriptomic and clinical characteristics of TARA infiltration. Third, we downloaded expression profiles of recurrent glioblastoma samples from patients receiving PD-1 inhibitors to analyze the predictive value of TARAs for immune checkpoint inhibition. Results: Single-cell RNA sequencing data showed TARAs were abundant in the glioma micro-environment (15.7% in the CGGA dataset and 9.1% in the Gene Expression Omnibus GSE141383 dataset, respectively). Bulk tumor sequencing data showed that the extent of TARA infiltration was highly associated with major clinical and molecular features of astrocytic gliomas. Patients with more TARA infiltration were more likely to have MUC16, FLG, and PICK3A mutations, chromosome 9p21.3, 10q23.3, and 13q14.2 deletions and 7p11.2 amplification. Gene Ontology analysis revealed that the high level of astrocyte infiltration was characterized by immune and oncogenic pathways, such as the inflammatory response, positive regulation of the JAK-STAT cascade, positive regulation of NIK/NF-kappa B signaling and the tumor necrosis factor biosynthetic process. Patients with greater TARA infiltration showed inferior prognosis. Meanwhile, the extent of reactive astrocyte infiltration exhibited a predictive value for recurrent glioblastoma patients undergoing anti-PD-1 immune therapy. Conclusion: TARA infiltration might promote glioma tumor progression and can be used as a diagnostic, predictive and prognostic marker in gliomas. Prevention of TARA infiltration might be a new therapeutic strategy for glioma.

Preclinical assessment of IRDye800CW-labeled gastrin-releasing peptide receptor-targeting peptide for near infrared-II imaging of brain malignancies.

We aimed to develop a new biocompatible gastrin-releasing peptide receptor (GRPR) targeted optical probe, IRDye800-RM26, for fluorescence image-guided surgery (FGS) of brain malignancies in near-infrared window II (NIR-II) imaging. We developed a novel GRPR targeting probe using a nine-amino-acid bombesin antagonist analog RM26 combined with IRDye800CW, and explored the fluorescent probe according to optical properties. Fluorescence imaging characterization in NIR-I/II region was performed in vitro and in vivo. Following simulated NIR-II image-guided surgery, we obtained time-fluorescent intensity curves and time-signal and background ratio curves. Further, we used histological sections of brain from tumor-beating mice model to compare imaging specificity between 5-aminolevulinic acid (5-ALA) and IRDye800-RM26, and evaluated biodistribution and biocompatibility. IRDye800-RM26 had broad emission ranging from 800 to 1200 nm, showing considerable fluorescent intensity in NIR-II region. High-resolution NIR-II imaging of IRDye800-RM26 can enhance the advantages of NIR-I imaging. Dynamic and real time fluorescence imaging in NIR-II region showed that the probe can be used to treat brain malignancies in mice between 12 and 24 h post injection. Its specificity in targeting glioblastoma was superior to 5-ALA. Biodistribution analysis indicated IRDye800-RM26 excretion in the kidney and liver. Histological and blood test analyses did not reveal acute severe toxicities in mice treated with effective dose (40 µg) of the probe for NIR-II imaging. Because of the considerable fluorescent intensity in NIR-II region and high spatial resolution, biocompatible and excretable IRDye800-RM26 holds great potentials for FGS, and is essential for translation into human use.

A regioselective [3 + 2] cycloaddition reaction of 2-benzylidene-1-indenones with functional olefins to access indanone-fused 2D/3D skeletons.

The regioselective [3 + 2] cycloaddition reaction of 2-benzylidene-1-indenones with functional olefins was established with DABCO as a base under mild conditions. Using this approach, a series of diversely substituted indanone-fused cyclopentane polycycles with highly crowded multiple substituents were synthesized in high yields.

Exploration of suitable external quality assessment materials for serum C-peptide measurement.

OBJECTIVES: To find suitable external quality assessment (EQA) materials for serum C-peptide, we evaluated the commutability of five types of processed materials. METHODS: Seventy-four individual serum samples and 12 processed samples including three EQA samples currently in use, frozen human serum pools (FHSP), and three other kinds of processed samples were prepared by dissolving WHO International Standard Reagent for C-peptide (WHO ISR 13/146) in three different matrixes: 0.05 % bovine serum albumin, fetal bovine serum and human serum pools. Samples were analyzed using the isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method and six widely used immunoassays. The commutabilities of processed materials were assessed according to the difference in bias approach recommended by the IFCC. And the short- and long-term stability of FHSP samples at different temperatures were also evaluated. RESULTS: Out of the five kinds of processed materials, FHSP samples were commutable on most assays. In contrast, the EQA materials currently in use were only commutable on a few immunoassays. Additionally, processed materials derived from WHO ISR 13/146 were found to be un-commutable on over half of immunoassays. The FHSP samples could be stably stored at 4 and -20 °C for at least 16 days, and at -80 °C for at least 1 year, but at room temperature only for 12 h. CONCLUSIONS: With clarified commutability and stability information, the human serum pool samples along with the developed ID-LC-MS/MS method could be used in the EQA program to promote the comparability among laboratories for C-peptide measurement in China.

Identification of distinct tumor cell patterns with single-cell RNA sequencing integrating primary lung adenocarcinoma and brain metastasis tumor.

Background: Lung adenocarcinoma (LUAD) is the most common form of lung cancer and is often accompanied by brain metastasis (BM). The heterogeneity of the tumor renders all current conventional treatments less effective. This study aims to dissect tumor cell heterogeneity and identify potential therapeutic targets. Methods: We conducted single-cell RNA-sequencing (scRNA-seq) in 8 patients with treatment-naïve LUAD BM and included scRNA-seq data of 10 primary LUAD samples and their matched adjacent normal tissue from GSE131907 to determine the tumor cell heterogeneity. Results: Our analyses revealed tumor cells derived from brain metastases were more heterogeneous. Tumor cells from BM harbored significantly more copy number variants (CNVs), and cells of magnoid subtype were the critical source of malignant cells both in BM and the primary lung tumor. Pseudo-time trajectory analysis revealed that malignant cells had upregulated genes enriched for cell cycle and cell division. Integrated analysis of tumor cells revealed 2 distinct malignant cell clusters (cluster 4 and cluster 6) and their marker genes. The signatures identified in the single-cell profile had prognostic value in the bulk tumor profiles. Moreover, the signature of cluster 4 had significant prognostic value in predicting patients surviving longer than 3.5 years, while the signature of cluster 6 showed better predictive ability within 1 year. Magnoid-type cells are most likely to develop into the riskiest cell type and potentially promote tumor progression. Conclusions: scRNA profiling that integrates LUAD BM and primary LUAD can provide information on those malignant cells with BM potential, offering additional prognostic information at cellular level, and may serve as a foundational resource for further tumor cell dissection and therapeutic target exploration.

Poor comparability of plasma renin activity measurement in determining patient samples: the status quo and recommendations for harmonization.

OBJECTIVES: This study aims to investigate and update the consistency and comparability of plasma renin activity (PRA) assays in measuring clinical samples. The contributions of recalibration, blank subtraction, and incubation strategies to interchangeability were also explored. METHODS: Five different laboratories were evaluated using forty-six individual plasma samples, including four liquid chromatography-tandem mass spectrometry (LC‒MS/MS) assays and one chemiluminescence immunoassay (CLIA). Spearman correlation coefficient (R), Passing-Bablok regression, and Bland‒Altman plot analyses were used to evaluate the consistency among assays. Consistency before and after recalibration, blank subtraction, and incubation strategy unification was compared. RESULTS: A good correlation was observed among all assays (R>0.93). None of the samples measured by all assays showed coefficient variation (CV) <10 %, and 37 % of samples showed overall CVs >20 %. The 95 % confidence intervals (CIs) for slopes did not contain 1 for most assay pairs. Large relative biases (-85.1-104.2 %) were found, and 76 % (52-93 %) of samples had unacceptable biases. Recalibration reduced the calibration bias. Ignoring blank subtraction improved the comparability across all assays while unifying incubation did not. CONCLUSIONS: The interchangeability of PRA measurement was unsatisfying. Harmonization on calibrator and ignoring blank were recommended. Unifying incubation strategy was unnecessary.

Evaluation of blood lead measurements by the 6-year external quality assessment program in China.

BACKGROUND: Blood lead is an important clinical indicator. A typical tool for promoting standardisation or harmonisation is external quality assessment (EQA). Therefore, the National Centre for Clinical Laboratories (NCCL) in China launched the EQA Program for blood lead measurement in 2006 to assess its standardisation process. METHODS: Blood lead EQA samples tested for homogeneity and stability were sent to participating laboratories. The return data were grouped according to the detection method. The robust mean value, robust coefficient of variation (CV) and standard uncertainty were calculated according to ISO 13528. The evaluation criteria were determined based on a thorough analysis of the previous pass rate and the current detection level. Overall trends in the blood lead EQA program over 6 years were investigated by calculating the pass rates of participating laboratories. We compared the pass rates and current issues of different detection methods and analysed the target values, bias and CV results of mainstream detection methods. RESULTS: A total of 4,283 laboratories participated in EQA programs from 2017 to 2022. The pass rates were generally increasing while the inter-laboratory mean CVs were decreasing. For samples with varying concentrations, the higher the concentration, the smaller the CV. According to the evaluation criteria, the most used measurement methods, Graphite Furnace Atomic Absorption Spectrometry (GFAAS) and Tungsten Ship Atomic Absorption Spectrometry (TSAAS) demonstrated better performances than Differential Potentiometric Stripping (DPS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Flame Atomic Absorption Spectrometry (FAAS). Furthermore, DPS, ICP-MS and FAAS outperformed Anodic Stripping Voltammetry (ASV). CONCLUSION: Our study provides reliable information on the standardisation of blood lead measurement procedures for manufacturers and clinical laboratories. Further improvements for standardisation are still required to make laboratories more patient-centred.

Imprecision remains to be improved in the measurement of serum cystatin C with heterogeneous systems.

OBJECTIVES: Except for the large bias of some measurement systems for serum cystatin C (CysC) measurements, unacceptable imprecision has been observed for the heterogenous system. This study analyzed the external quality assessment (EQA) results in 2018-2021 to provide an insight into the imprecision of CysC assays. METHODS: Five EQA samples were sent to participating laboratories every year. Participants were divided into reagent/calibrator-based peer groups, for which the robust mean of each sample and robust coefficient of variation (CV) were calculated by Algorithm A from ISO 13528. Peers with more than 12 participants per year were selected for further analysis. The limit of CV was determined to be 4.85% based on clinical application requirements. The concentration-related effect on CVs was investigated using logarithmic curve fitting; the difference in medians and robust CVs between instrument-based subgroups was also evaluated. RESULTS: The total number of participating laboratories increased from 845 to 1,695 in four years and heterogeneous systems remained the mainstream (≥85%). Of 18 peers with ≥12 participants, those using homogeneous systems showed relatively steady and small CVs over four years, with the mean four-year CVs ranging from 3.21 to 3.68%. Some peers using heterogenous systems showed reduced CVs over four years, while 7/15 still had unacceptable CVs in 2021 (5.01-8.34%). Six peers showed larger CVs at the low or high concentrations, and some instrument-based subgroups presented greater imprecision than others. CONCLUSIONS: More efforts should be made to improve the imprecision of heterogeneous systems for CysC measurement.

An Accurate Isotope Dilution Liquid Chromatography-Tandem Mass Spectrometry Method for Serum C-Peptide and Its Use in Harmonization in China.

Background: Serum C-peptide results from various routine methods used in China are highly variable, warranting well-performing methods to serve as an accuracy base to improve the harmonization of C-peptide measurements in China. We developed an accurate isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method for serum C-peptide measurement and explored its use in harmonization. Methods: After protein precipitation with ZnSO4 solution, C-peptide was extracted from serum samples by anion-exchange solid-phase extraction and quantified by ID-LC-MS/MS in positive ion mode. The precision and analytical recovery of the ID-LC-MS/MS method were assessed. Seventy-six serum samples were analyzed using the ID-LC-MS/MS method and six routine immunoassays. Ordinary linear regression (OLR) and Bland-Altman (BA) analyses were conducted to evaluate the relationship between the ID-LC-MS/MS method and routine immunoassays. Five serum pool samples assigned using the ID-LC-MS/MS method were used to recalibrate the routine assays. OLR and BA analyses were re-conducted after recalibration. Results: The within-run, between-run, and total precision for the ID-LC-MS/MS method at four concentrations were 1.0%-2.1%, 0.6%-1.2%, and 1.3%-2.2%, respectively. The analytical recoveries for the ID-LC-MS/MS method at three concentrations were 100.3%-100.7%, 100.4%-101.0%, and 99.6%-100.7%. The developed method and the immunoassays were strongly correlated, with all R2 >0.98. The comparability among the immunoassays was substantially improved after recalibration. Conclusions: The performance of the ID-LC-MS/MS method was carefully validated, and this method can be used to improve the harmonization of serum C-peptide measurements in China.