Continuous improvement of medical test reliability using reference methods and matrix-corrected target values in proficiency testing schemes: Application to glucose assay

The reliability of biological tests is a major issue for patient care in terms of public health that involves high economic stakes. Reference methods, as well as regular external quality assessment schemes (EQAS), are needed to monitor the analytical performance of field methods. However, control material commutability is a major concern to assess method accuracy. To overcome material non-commutability, we investigated the possibility of using lyophilized serum samples together with a limited number of frozen serum samples to assign matrix-corrected target values, taking the example of glucose assays. Trueness of the current glucose assays was first measured against a primary reference method by using human frozen sera. Methods using hexokinase and glucose oxidase with spectroreflectometric detection proved very accurate, with bias ranging between -2.2% and +2.3%. Bias of methods using glucose oxidase with spectrophotometric detection was +4.5%. Matrix-related bias of the lyophilized materials was then determined and ranged from +2.5% to -14.4%. Matrix-corrected target values were assigned and used to assess trueness of 22 sub-peer groups. We demonstrated that matrix-corrected target values can be a valuable tool to assess field method accuracy in large scale surveys where commutable materials are not available in sufficient amount with acceptable costs.     

Pilot external quality assessment survey for post-market vigilance of in vitro diagnostic medical devices and investigation of trueness of participants' results.

The Czech External Quality Assessment Scheme organized a survey using 14 fresh-frozen sera targeted for cholesterol and glucose by reference measurement procedures. The objective was to investigate whether it could fulfil a post-market vigilance function for in vitro diagnostic medical devices and assess trueness of participants' results. It revealed a mean bias of +5.1% for cholesterol and +3.7% for glucose (n approximately 150). However, the bias source (manufacturer or laboratory) could not be identified unequivocally because of the lack of homogeneous groups. This was due to the fact that laboratories mainly used reagents from manufacturers that do not market instruments or combined calibrators and reagents from different sources. Consequently, these habits did not allow the survey to fulfil the vigilance function. On the other hand, we were able to show the individual participants results for patient samples deviating from the true value (deviations >10% in approximately 20% of the laboratories). However, again, the survey failed in problem-solving via peer-group evaluation, even for participants that applied homogeneous tests. If other European schemes confirm this outcome, cooperation and/or participation of manufacturers may be the solution. The survey pointed out to the other participants, interchanging instrument, reagent and calibrator, that they are themselves responsible for the problems shown and hence also for problem-solving.     

External Quality Assessment in The Netherlands: time to introduce commutable survey specimens. Lessons from the Dutch "Calibration 2000" project.

The performance of suitable secondary reference material for the use of trueness control of six routinely measured clinical enzymes in the Dutch External Quality Assessment (EQA) scheme is described. The reference material of choice was selected using the split-patient-sample between-field method (twin study) design as described in an earlier study of the Calibration 2000 project in The Netherlands. This material, which was proven to be commutable for all wet chemistry systems, was implemented as the national enzyme calibrator. It consisted of a cryo-protected lyophilised serum with additions of recombinant human enzymes. Various batches of the frozen version of this material without cryo-protection additive, called native EQA samples, were used in the general EQA scheme for performance evaluation. The results of Calibration 2000 calibrated and non-Calibration 2000 calibrated laboratories were compared for both the regular (spiked with non-human enzymes) and native EQA samples in terms of precision and bias with established reference method values for the native samples. The regular samples showed mean between-laboratory CV ranges for all six enzymes involved (low-high) of 5.5-10.3% for the non-calibrated users vs. 4.6-10.8% for the calibrated users. For the native samples these respective ranges were 5.2-9.9% vs. 2.2-4.9%. Without exception, the group of Calibration 2000 calibrated users showed the lowest bias against the reference method values. Regular EQA samples (spiked with non-human enzymes) showed poorer performance than native samples and are not suitable for accuracy assessment purposes, the main aim of EQA schemes. Native samples that are commutable should be used for trueness control in current EQA schemes.     

Quality specifications in EQA schemes: from theory to practice

BACKGROUND: External quality assessment (EQA) is a tool for quality management in clinical laboratories and its main objectives are assessment of participants and methods performance, training and advice. This paper describes the quality specifications used in EQA schemes of the Centre of Biomedical Research (CRB), in order to design schemes that can assess laboratory reliability performances, meet the changing needs and quality recommendations. METHODS: Quality specifications for control materials, statistical procedures and goals to assess laboratory performance have been applied and introduced in EQA schemes managed by CRB. RESULTS: The application of well-defined quality specifications has demonstrated effective. In particular, we report results on alkaline phosphatase and cholesterol obtained using commercial control materials and human serum controls, in two different EQA surveys; the inter-laboratory variability (CVinter%) for troponin I analysed with a diagnostic system and assigned values of CK-MB mass obtained using four different diagnostic systems; the percentage of acceptable performances obtained by means of the application of goals based on clinical criteria, biological variation, state-of-the-art and used for EQA schemes, and referring to some analytes with significant clinical values such as cholesterol, glucose, glycated hemoglobin and sodium. CONCLUSIONS: The design of reliable EQA schemes based on evidence-based quality specifications is a pre-requisite for supporting the quality improvement of clinical laboratories.     

Between-lot variation in external quality assessment of glucose: clinical importance and effect on participant performance evaluation

BACKGROUND: External quality assessment schemes (EQAS) are conducted to evaluate user performance (participant assessment) and to assess different methods and instruments (method assessment). The quality of control materials is crucial to achieving these goals. Inconsistencies in between-lot variations detected by use of different control and sample materials may affect EQAS outcomes. METHODS: For the Accu-Chek Sensor, Precision Xtra, Ascensia Elite, and HemoCue 201 glucometers, 3 different lots of glucose strips were used with each instrument. Method assessment results from analysis of capillary blood and 3 control materials were used to calculate between-lot differences. A simulation study was performed to evaluate the effect of between-lot variation on participant assessment results. RESULTS: With the Precision Xtra, the results obtained with EQA control material mirrored those obtained with capillary blood, but for the other instruments, we found between-lot differences of as much as 1.3 mmol/L, which were substantially greater than those found with capillary blood and of clinical importance at decision limits. The simulation study showed an effect on participant assessment results related to the target values, with the percentage of poor results decreasing (38%, 10%, and 4%) with the use of common, method-specific, and lot-specific target values, respectively. CONCLUSIONS: Between-lot variation may influence participant EQA results for participant and method assessments. The clinical relevance of between-lot variation discovered in EQAS using noncommutable control materials should be examined by use of native blood samples.     

Quality of serum creatinine measurement in light of EQA programs.

BACKGROUND: The aim of our study was to identify the role of External Quality Assessment (EQA) programs in improving the quality of serum creatinine measurement and glomerular filtration rate (GFR) estimation. Comparison of results achieved during EQA with National Kidney Disease Education Program and College of American Pathologists guidelines identified an urgent need for an improvement in measurement quality. We compared actual results for serum creatinine measurement within the Czech Republic EQA with the requirements of EC Directive 98/79. METHODS: We used the results for 2005-2006 EQA programs. There were seven surveys involved with two samples each, and a 2006 questionnaire on the post-analytical phase survey. RESULTS: Bias depended strongly on the creatinine concentration. However, this dependence varied for different in vitro diagnostic manufacturers, although they should all follow the same directive. We chose biological variation as the significance rate for bias and a resulting overall error of 6.9%. The proportion of results with total error <6.9% ranged from 11% to 80%. The total error for a reference sample of 94.8 mumol/L also showed significant dependence on the working calibrator used and ranged from 1% to 17%. CONCLUSIONS: The main role of EQA programs in improving the quality of creatinine measurement results and GFR calculation should be in monitoring the quality of IVD products, enabling users to adapt their use of these products accordingly. EQA programs can also educate on performing GFR estimation in a unified way. Highly commutable control materials with certified creatinine values or, alternatively, lyophilized materials with sufficient commutability proved by comparison with native frozen human sera, should become an important EQA tool.     

Experience with an external quality assessment programme for point-of-care-testing (POCT) devices for the determination of blood glucose

This article describes the preparation and internal and external evaluation of materials, critical issues in the external quality assessment (EQA) of point-of-care testing (POCT) devices for measuring blood glucose. A comparison was made between different materials, both of natural and synthetic origin and with and without stabilisers. The aims were to produce a material which was compatible with as many POCT-devices as possible and so reduce the number of materials sent out in each campaign as well as to optimise the precision and comparability of results between methods and devices. Although the use of near natural material--sterile-filtered plasma spiked with glucose--survived internal testing, this material proved to be unsuitable for EQA surveys. The study resulted in the reduction of materials for each survey to stabilised whole blood for one device, stabilised plasma for two devices and a synthetic material based on a polyethylene glycol matrix for all other devices. Samples were sent as pairs six times annually. The POCT-devices tested measured precisely but inaccurately in the synthetic material, when compared with the reference method (gas-chromatography coupled with isotope-dilution mass-spectrometry; GC-IDMS), so that the devices could only be evaluated for precision. The construction of ratios between the concentrations measured on the two samples distributed allowed an indirect assessment of accuracy. The need for surveillance of POCT devices is stressed in this publication, which combines theory and practice in setting up and running an EQA programme for blood glucose.     

Minimally processed fresh frozen human reference sera: preparation, testing, and application to international external quality assurance

The preparation of unmodified or minimally processed fresh frozen human sera is described, as well as the previous use of such sera, e.g. in Nordic and international external quality assurance (EQA) activities. The unmodified serum is prepared from fresh donors' blood collected in dry bags and allowed to coagulate. The serum is collected "on the clot", pooled, filtered, mixed, dispensed in polypropylene vials and frozen at -80 degrees C without further processing. Some batches were slightly modified by spiking or dilution. Critical steps of the production and use of the sera are described and improvements are discussed. A total of 34 different batches have been prepared since 1985. Results from homogeneity and stability studies are presented. The studies cover 18 routine components in serum stored at +4 degrees C to 37 degrees C for up to 34 days. Good stability was observed for storage of all components, with the exception of triglyceride. Amylase, creatininium, glucose, gamma-glutamyltransferase, urate (and perhaps carbamide) showed deterioration after 13 days of incubation at 37 degrees C. The long-term stability at -80 degrees C is reviewed and new data are presented, e.g. as consensus values from EQA schemes, where the same serum has been sent out three times over 5 years, and from reference measurement procedure values that have been assigned twice with an interval of 5 years. Furthermore, a 10-year stability study has been started.     

三级公立医院绩效考核第13项指标室间质量评价的解读

根据《国务院办公厅关于加强三级公立医院绩效考核工作的意见(国办发〔2019〕4号)》"三级公立医院绩效考核指标"的第13项指标"通过国家室间质量评价的临床检验项目数",国家卫生健康委临床检验中心开发了信息采集系统,建立实验室室间质评项目参加率和合格率分析系统。近3年,参加室间质量评价的三级公立医院数量有所上升,室间质评项目参加率中位数有所提高,室间质评项目合格率中位数相对稳定。通过国家卫生健康委临床检验中心组织的室间质量评价项目数量的监测,对三级公立医院临床实验室室间质评项目参加率和合格率进行统计分析,推动三级公立医院重视室间质量评价,持续改进质量,以提高检测的有效性和可比性。     

Serum cholesterol during 27 years: assessment of systematic error and affecting factors and their role in interpreting population trends

BACKGROUND: The aim was to assess which factors cause a systematic error in serum total cholesterol measurements and how bias can influence the interpretation of serum cholesterol changes of the Finnish population. METHODS: Data on precision and accuracy during 27 years for serum total cholesterol were documented from participation in 438 rounds of five different external quality assessment (EQA) programs. RESULTS: The mean annual accuracy (bias) of the cholesterol assay using the results from all EQAs during 1978-2004 was -0.74% (95%CI -0.88 to -0.60). An exceptionally large deviation in bias coincided with the introduction of a new serum calibrator lot. New methods or instrumentation had only a minor impact on serum cholesterol bias. The mean serum cholesterol bias during the latest five population studies in 1982-2002 was -0.10% (95%CI -0.60 to 0.40) but comparison of the bias between the last study (CDC EQA in 2002) and the four previous ones (WHO EQA) showed a net difference of 3.32% (p<0.001). Correcting the mean serum cholesterol of men with respect to WHO and CDC EQA bias changed the interpretation for the last two survey years from an increase of 1.8% to no change. CONCLUSIONS: It is necessary to participate in EQA programs, which include target values measured by the CDC cholesterol reference method and then to perform bias corrections on the mean cholesterol values of the populations.     

Problems with the external quality assessment of accuracy of point of care devices (POCD) for blood glucose are independent of sample composition

This short article describes the results obtained in both internal and external quality assessment of point of care devices (POCD) for the monitoring of blood glucose. The results show that the use of synthetic, serum and whole blood matrices for the samples do not markedly change the inaccuracy of measurement. It is only possible to check precision of POC devices for glucose in external quality assessment (EQA) surveys for POC devices for blood glucose. The majority of devices used in point of care testing for blood glucose had acceptable (im)precision. The applications and limitations of the use of POC devices for blood glucose must be clearly defined before allowing their use in patient care programmes. Finally, the results confirm that the decision of the German Federal Medical Council (Bundes?rztekammer) to exclude POC devices from accuracy checks against a reference method procedure in national EQA surveys was correct, at least at the present time.     

血清尿素测定基质效应研究

目的 评价2007年全国室间质量评价(EQA)临床化学项目材料和13种市售制备物血清尿素测定在7种脲紫外速率法测定系统上的基质效应,并考察这些测定系统的校准偏差.方法 按美国临床和实验室标准协会(CLSI)EP 14-A2试验方案,同位素稀释气相色谱质谱法作比对方法,7种尿素酶常规方法为待评方法,用比对方法和待评方法同时测定25份新鲜冰冻人血清和EQA材料及市售制备物.考察常规方法和比对方法测定EQA材料(或市售制备物)结果间的数量关系与它们测定新鲜冰冻人血清样品数量关系的一致程度,评价样品的基质效应.考察新鲜冰冻人血清样品常规方法和比对方法结果的差异,评价测定系统的校准偏差.结果 8种EQA材料和3种市售制备物对参加评价的所有测定系统无基质效应,1种市售制备物对所有系统都表现基质效应,其他样品视系统的不同而表现出不同的情况.7种测定系统中的6种都存在不同程度的校准偏差:同直线Y=X相比,系统A的斜率、截距偏差均小于5%,不存在明显校准偏差.系统B、C、D、F、G的斜率偏差小于5%,截距偏差大于5%,存在一定的校准偏差.系统E的斜率和截距偏差均大于5%,表现为存在校准偏差.结论 样品的基质效应和测定系统的校准偏差影响血清尿素测定的准确性和可比性.应充分重视基质效应和校准偏差对临床检验量值溯源的影响.     

Preparation of fresh frozen human sera for external quality assessment

A procedure for preparation of unmodified and modified fresh frozen human quality testing sera is described. The materials have been used for external quality assessment in Denmark. Examples of improvements in external quality assessment schemes using this type of material are shown.     

apo A1和apo B侯选参考方法在室间质量评价中的应用价值

目的 探讨载脂蛋白(apo)A1和apo B的候选参考方法 在室间质量评价(EQA)中的应用价值.方法 以5个水平的冰冻人血清制品作为EQA质评物,采用免疫透射比浊法(ITA)检测.采用同位素稀释液相色谱串联质谱(ID-LC-MS/MS)定量技术对EQA样本进行定值,包括变性、烷基化和胰蛋白酶酶解处理,使用C18色谱柱...     

2008至2009年度上海市糖化血红蛋白项目室间质评结果分析

目的分析上海市2008~2009年度糖化血红蛋白（HbA1c）项目室间质评结果,为提高HbA1c检测质量提供依据。方法收集2008~2009年参加上海市临床检验中心HbA1c室间质评医院的4次调查结果,对结果进行统计分析。结果 2008~2009年上海市开展糖化血红蛋白室间质评的医院数从2008年122家增加至2009年178家,合格率从2008年96.7%增加到2009年98.9%。部分的调查结果离散度〉10%[2008年第1次的低压液相（LPLC）1号样本（10.8%）、免疫比浊法2份人新鲜全血样本（15.4%和15.9%）;2008年第2次的免疫比浊法2号样本（10.5%）;2009年第1次的微粒色谱法2号样本（10.3%）;2009年第2次的微粒色谱法2号样本（11.0%）和免疫比浊法1号样本（10.0%）]。经过质控管理,至2009年第2次调查,整体的平均变异系数（CV）有明显改进,人新鲜全血样本各检测系统的结果无明显差异,除微粒色谱法外,符合率达到100%。结论通过加强质控管理,开展HbA1c标准化工作,推动HbA1c检测结果的准确、可比,为临床提供可靠的诊疗依据。     

Methodologic European external quality assurance for DNA sequencing: the EQUALseq program

BACKGROUND: DNA sequencing is a key technique in molecular diagnostics, but to date no comprehensive methodologic external quality assessment (EQA) programs have been instituted. Between 2003 and 2005, the European Union funded, as specific support actions, the EQUAL initiative to develop methodologic EQA schemes for genotyping (EQUALqual), quantitative PCR (EQUALquant), and sequencing (EQUALseq). Here we report on the results of the EQUALseq program. METHODS: The participating laboratories received a 4-sample set comprising 2 DNA plasmids, a PCR product, and a finished sequencing reaction to be analyzed. Data and information from detailed questionnaires were uploaded online and evaluated by use of a scoring system for technical skills and proficiency of data interpretation. RESULTS: Sixty laboratories from 21 European countries registered, and 43 participants (72%) returned data and samples. Capillary electrophoresis was the predominant platform (n = 39; 91%). The median contiguous correct sequence stretch was 527 nucleotides with considerable variation in quality of both primary data and data evaluation. The association between laboratory performance and the number of sequencing assays/year was statistically significant (P <0.05). Interestingly, more than 30% of participants neither added comments to their data nor made efforts to identify the gene sequences or mutational positions. CONCLUSIONS: Considerable variations exist even in a highly standardized methodology such as DNA sequencing. Methodologic EQAs are appropriate tools to uncover strengths and weaknesses in both technique and proficiency, and our results emphasize the need for mandatory EQAs. The results of EQUALseq should help improve the overall quality of molecular genetics findings obtained by DNA sequencing.     

2004～2008年湖南省尿液干化学室间质量评价结果分析

目的探讨影响湖南省临床实验室尿液干化学检测结果准确性的因素,并提出相应的改进措施和建议。方法对2004～2008年室间质量评价(EQA)回报数据和现场检测的相关情况进行分析。结果 5年全省尿液干化学室间质评参评实验室从157家增加到214家;参评实验室合格率2004年为80.3%,2005年为89.7%,2006～2008年为93.8%～94.1%;能力验证得分和及格率较低的项目有尿胆原(89.2%、81.2%)、白细胞(91.6%、89.6%)、葡萄糖(91.9%、89.6%),其余项目均在95.0%以上;现场检测共计抽查101家实验室,平均合格率95.1%,但问卷调查存在问题较多。结论全省尿液干化学参评情况不理想。部分参评实验室EQA成绩不满意与不开展室内质控、试纸条与尿液分析仪的非配套使用、仪器的保养与维护等因素有关。     

Precision of glucose measurements in control sera by isotope dilution/mass spectrometry: proposed definitive method compared with a reference method

This improved isotope-dilution gas chromatographic/mass spectrometric (GC/MS) method, in which [13C]glucose is the internal standard, meets the requirements of a Definitive Method. In a first study with five reconstituted lyophilized sera, a nested analysis of variance of GC/MS values indicated considerable among-vial variation. The CV for 32 measurements per serum ranged from 0.5 to 0.9%. However, concentration and uncertainty values (mmol/L per gram of serum) assigned to one serum by the NBS Definitive Method (7.56 +/- 0.28) were practically identical to those obtained with the proposed method (7.57 +/- 0.20). In the second study, we used twice more [13C]glucose diluent to assay four serum pools and two lyophilized sera. The CV ranged from 0.26 to 0.5% for the serum pools and from 0.28 to 0.59% for the lyophilized sera. In comparison, results by the hexokinase/glucose-6-phosphate dehydrogenase reference method agreed within acceptable limits with those by the Definitive Method but tended to be slightly higher (up to 3%) for lyophilized serum samples or slightly lower (up to 2.5%) for serum pools.     

脑脊液生化检测室内质量控制不精密度分析及Westgard西格玛规则的应用

目的 分析脑脊液生化检测项目室内质量控制不精密度及Westgard西格玛规则在葡萄糖项目室内质量控制(IQC)中的应用。方法 收集2014～2017年参加卫生部临床检验中心室间质量评价(EQA)单位回报的IQC数据,依据1/3TEa(室间质量评价限),1 /4TEa计算得到满足两种标准的实验室比例。根据IQC所使用的检测系统进行分组统计,并按两个评价标准计算各组的通过率。随机选择2017年10家同时上报葡萄糖项目EQA和IQC的实验室,以EQA中的百分差值作为偏倚(bias)估计值,以IQC的累积变异系数作为不精密度估计值,以EQA计划中的允许总误差TEa作为质量规范,依据公式σ=[(TEa-|bias|)/CV]计算σ值。结果 2014～2017年间清蛋白、总蛋白、氯化物3个项目达到两种标准的不精密度性能规范的实验室比例较低。葡萄糖、乳酸脱氢酶、IgA,IgG,IgM和乳酸6个项目通过率相对较高,且各项目的通过率略有上升趋势。使用不同检测系统的通过率比例参差不齐,并无规律。使用Westgard西格玛规则为葡萄糖项目选择合适的质控规则。3号实验室σ值>6,6σ质量应选择1_3s规则; 2,5,7号σ值分别为4.84,4.47和4.72,4σ质量水平应选择1_3s/2_2s/R_4s/4_1s规则; 其余实验室σ值均<4,选用1_3s/2_2s/R_4s/4_1s/8x规则。结论 各项目的IQC不精密度水平存在很大差距,各实验室应建立严格的IQC程序,积极参与IQC数据实验室间比对,进一步提高脑脊液生化检测的水平,并通过Westgard西格玛规则为实验室检测项目选择正确的质控规则。     

TORCH血清学检测室间质量评价分析

目的 对目前国内临床实验室TORCH血清学检测情况进行评价.方法 通过室间质量评价的方式:每年进行2次室间质评,每次发放5支质评样本;要求各临床实验室在规定时间内检测、回报检测结果、所用的检测方法、仪器和试剂;卫生部临床检验中心对各实验室的结果进行统计分析,将结果反馈给各实验室,同时对检测结果、试剂情况进行评价.结果 2007年单纯疱疹病毒(HSV)IgM、风疹病毒(Rubella virus)IgM和巨细胞病毒(CMV)lgM 3个项目临床实验室检测合格率均达到了80%以上,弓形虫(Toxo)IgM符合率较低,仅53.1%.试剂的使用评价分析显示,不同试剂各个项目的 阳性符合率均较低(均小于80%).相同的试剂在不同的实验室检测得到的样本吸光度(A)值与阳性结果判定值的比值(S/CO值)有很大差异.结论 TORCH血清学检测室间质量评价反映出多数实验室得到了满意的成绩(PT≥80),但阳性样本的检出率较低,除试剂的原因,也有实验室工作人员操作方面的原因.