Trueness verification of actual creatinine assays in the European market demonstrates a disappointing variability that needs substantial improvement. An international study in the framework of the EC4 creatinine standardization working group

Abstract Background: The European In Vitro Diagnostics (IVD) directive requires traceability to reference methods and materials of analytes. It is a task of the profession to verify the trueness of results and IVD compatibility. Methods: The results of a trueness verification study by the European Communities Confederation of Clinical Chemistry (EC4) working group on creatinine standardization are described, in which 189 European laboratories analyzed serum creatinine in a commutable serum-based material, using analytical systems from seven companies. Values were targeted using isotope dilution gas chromatography/mass spectrometry. Results were tested on their compliance to a set of three criteria: trueness, i.e., no significant bias relative to the target value, between-laboratory variation and within-laboratory variation relative to the maximum allowable error. Results: For the lower and intermediate level, values differed significantly from the target value in the Jaffe and the dry chemistry methods. At the high level, dry chemistry yielded higher results. Between-laboratory coefficients of variation ranged from 4.37% to 8.74%. Total error budget was mainly consumed by the bias. Non-compensated Jaffe methods largely exceeded the total error budget. Best results were obtained for the enzymatic method. The dry chemistry method consumed a large part of its error budget due to calibration bias. Conclusions: Despite the European IVD directive and the growing needs for creatinine standardization, an unacceptable inter-laboratory variation was observed, which was mainly due to calibration differences. The calibration variation has major clinical consequences, in particular in pediatrics, where reference ranges for serum and plasma creatinine are low, and in the estimation of glomerular filtration rate. Clin Chem Lab Med 2008;46:1319-25.     

Determination of serum creatinine by Jaffe method and how to calibrate to eliminate matrix interference problems

BACKGROUND: The calibration of Jaffe method for serum creatinine using one serum-based standard complemented with artificial matrix compensating standard's Jaffe-interfering substances allows two-point calibration with results well comparable with enzymatic methods. METHOD: Spectrophotometry was used. RESULTS: Jaffe procedures compensating serum/plasma intereferents by subtracting a constant amount of creatinine poorly overcompensate creatinine in children. Two-point calibration with a pair of primary serum standards certified by the reference measurement procedure (isotope-dilution, mass spectrometry) or with a pair of secondary standards linked to primary materials could provide results well agreeable with enzymatic determination. Such a calibration comprises an absorbance offset corresponding to other-than-creatinine Jaffe-interfering chromogens present in standards in the calibration line, while a two-point calibration combining one standard with physiological saline/water always grossly distorts calibration line. We calculated/prepared artificial serum matrices capable of compensating Jaffe-interfering chromogens in serum standards. The combination of even one standard with its artificial matrix also enables two-point calibration with practically the same results as with a pair of primary standards. CONCLUSIONS: A two-point calibration of Jaffe method for serum creatinine combining only one serum standard with creatinine solution matching standard's allow matrix-present interferents present results well comparable with enzymatic determination, providing the standard is attested/linked to the reference measurement procedure.     

Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program

BACKGROUND: Reliable serum creatinine measurements in glomerular filtration rate (GFR) estimation are critical to ongoing global public health efforts to increase the diagnosis and treatment of chronic kidney disease (CKD). We present an overview of the commonly used methods for the determination of serum creatinine, method limitations, and method performance in conjunction with the development of analytical performance criteria. Available resources for standardization of serum creatinine measurement are discussed, and recommendations for measurement improvement are given. METHODS: The National Kidney Disease Education Program (NKDEP) Laboratory Working Group reviewed problems related to serum creatinine measurement for estimating GFR and prepared recommendations to standardize and improve creatinine measurement. RESULTS: The NKDEP Laboratory Working Group, in collaboration with international professional organizations, has developed a plan that enables standardization and improved accuracy (trueness) of serum creatinine measurements in clinical laboratories worldwide that includes the use of the estimating equation for GFR based on serum creatinine concentration that was developed from the Modification of Diet in Renal Disease (MDRD) study. CONCLUSIONS: The current variability in serum creatinine measurements renders all estimating equations for GFR, including the MDRD Study equation, less accurate in the normal and slightly increased range of serum creatinine concentrations [<133 micromol/L (1.5 mg/dL)], which is the relevant range for detecting CKD [<60 mL.min(-1).(1.73 m2)(-1)]. Many automated routine methods for serum creatinine measurement meet or exceed the required precision; therefore, reduction of analytical bias in creatinine assays is needed. Standardization of calibration does not correct for analytical interferences (nonspecificity bias). The bias and nonspecificity problems associated with some of the routine methods must be addressed.     

血清肌酐测定基质效应的研究

目的 评价血清肌酐测定常规方法的校准偏差及肌酐制备物常在常规方法上的基质效应.方法 根据美国临床实验室和标准化协会(CLSI)EP14-A2评价方案,同位素稀释液相色谱串联质谱法(ID-LC/MS/MS)测定血清肌酐的方法为比对方法,15种常规肌酐测定系统(7种酶法,8种苦味酸法)为待评方法,测定40个新鲜冰冻人血清和36种制备物的肌酐浓度,评价制备物的基质效应和测定系统的校准偏差.结果 大部分商品制备物(29/30)在苦味酸法系统上表现出基质效应,少部分商品制备物(13/30)在部分酶法系统上表现出基质效应.我中心6个制备物在所有15个系统上均未观察到基质效应.所有常规系统新鲜冰冻血清测定值与比对方法测定值间均呈较好的直线相关,所有苦味酸法和部分酶法测定肌酐方法存在校准偏差.结论 基质效应和校准偏差存在于常规肌酐测定方法,必须重视这些因素,提高肌酐测定结果的正确度和可比性.     

Evaluation of the IRMA TRUpoint and i-STAT creatinine assays

BACKGROUND: The i-STAT (Abbott Diagnostics, East Windsor, NJ) and IRMA TRUpoint (ITC, Edison, NJ) POCT analyzers were evaluated in an oncology center. METHODS: Precision and agreement with our core laboratory creatinine was judged by comparison of 50 consecutive chemotherapy patient results against the Roche rate-blanked Jaffe and enzymatic creatinine methods. Glomerular filtration rate (GFR) was estimated using the Cockroft-Gault (CG) calculation and Modification of Diet in Renal Disease Study (MDRD) equation. RESULTS: Precision varied from 1% (enzymatic)-6.1% (TRUpoint). Correlation was good (r>0.9948) with slopes within 5% of the Jaffe and enzymatic methods. Intercepts were <15.9 micromol/l (<0.18 mg/dl), and statistically significant bias (p<0.0025) was noted between the mean of patient specimens for i-STAT correlations to both the Jaffe and enzymatic laboratory creatinine methods. There was statistically significant concordance of estimated GFR between all methods, however, the agreement of estimated GFR to either the Jaffe or enzymatic creatinine laboratory methods was better for the TRUpoint (by either MDRD or CG estimation) and i-STAT (by MDRD equation) (Kappa>0.60) than the i-STAT (by CG estimation) (Kappa=0.41-0.60). CONCLUSION: Small biases in the calibration of analytical creatinine methods can lead to differences in clinical concordance using estimated GFR. Selecting an optimal POCT method depends on the institution's current creatinine method and tolerance for analytical performance and clinical concordance.     

Limitations of compensated Jaffe creatinine assays in cirrhotic patients

ObjectivesThis study aimed to evaluate the impact of two creatinine measurement methods on the Model for End Stage Liver Disease (MELD) score and glomerular filtration rate estimation (eGFR) in cirrhotic patients. We focused on ID-MS traceable method such as compensated Jaffe (cJafCreat) and enzymatic (EnzCreat) methods.Design and methodsPotential protein-related interferences in creatinine determination were evaluated using dialysates spiked with albumin. MELD score, CKD-EPI formula creatinine-based eGFR and cystatin C-based eGFR were evaluated in 100 cirrhotic patients.ResultsIn vitro model demonstrated that low protein levels result in an underestimation of creatinine levels using cJafCreat. In patients, cJafCreat created a negative bias of ? 6.1 μmol/L that led to higher eGFR and lower MELD scores.ConclusionscJafCreat contributes to an overestimation of renal function in cirrhotic patients and may alter cirrhosis-severity assessment. Compensated Jaffe assays should therefore be replaced by enzymatic methods.     

Application of a six sigma model to the evaluation of the analytical performance of serum enzyme assays and the design of a quality control strategy for these assays: A multicentre study

BackgroundSix medical testing laboratories at six different sites in China participated in this study. We applied a six sigma model for (a) the evaluation of the analytical performance of serum enzyme assays at each of the laboratories, (b) the design of individualized quality control programs and (c) the development of improvement measures for each of the assays, as appropriate.MethodsInternal quality control (IQC) and external quality assessment (EQA) data for selected serum enzyme assays were collected from each of the laboratories. Sigma values for these assays were calculated using coefficients of variation, bias, and total allowable error (TEa). Normalized sigma method decision charts were generated using these parameters. IQC design and improvement measures were defined using the Westgard sigma rules. The quality goal index (QGI) was used to assist with identification of deficiencies (bias problems, precision problems, or their combination) affecting the analytical performance of assays with sigma values <6.ResultsSigma values for the selected serum enzyme assays were significantly different at different levels of enzyme activity. Differences in assay quality in different laboratories were also seen, despite the use of identical testing instruments and reagents. Based on the six sigma data, individualized quality control programs were outlined for each assay with sigma <6 at each laboratory.ConclusionsIn multi-location laboratory systems, a six sigma model can evaluate the quality of the assays being performed, allowing management to design individualized IQC programs and strategies for continuous improvement as appropriate for each laboratory. This will improve patient care, especially for patients transferred between sites within multi-hospital systems.     

Impact of serum creatinine measurement error on dose adjustment in renal failure

BACKGROUND: Doses of renally eliminated drugs should be adjusted according to kidney function to prevent adverse drug events and cost. Dose adjustment can be based on serum creatinine level, subsequent creatinine clearance estimation, and dosage calculation with consideration of the renal elimination properties of the respective compound. OBJECTIVE: Our objective was to quantify the impact and relevance of serum creatinine measurement error on dose adjustment in renal failure. METHODS: We analyzed 27914 measurements from external quality assessment surveys of 1878 German laboratories that used a kinetic alkaline picrate (69% of results) or an enzymatic method (25%) for creatinine determination. Linear models were fit for both methods combined and separately. On the basis of 95% confidence intervals (CIs) for creatinine values, 95% CIs for drug dosing were calculated. RESULTS: The 95% CI for a measured serum creatinine value was 0.80. Measured value < Reference method value < 1.28. Measured value for the kinetic alkaline picrate method and 0.87. Measured value < Reference method value < 1.21. Measured value for the enzymatic method. Applied to a data set of 6.5 million simulated patients with all possible combinations of characteristics relevant for drug dosing, the dosing error caused by serum creatinine measurement error did not exceed 25% in patients with creatinine clearance estimates lower than 50 mL/min according to the Cockcroft-Gault equation. For drugs completely eliminated by the kidneys in active form, the dosing error was up to 6-fold smaller than that which would occur if doses were not adjusted. CONCLUSION: The serum creatinine measurement error of current laboratory methods is small and is comparable to other errors influencing dose adjustment.     

Application of a six sigma model to evaluate the analytical performance of urinary biochemical analytes and design a risk‐based statistical quality control strategy for these assays: A multicenter study

BackgroundThe six sigma model has been widely used in clinical laboratory quality management. In this study, we first applied the six sigma model to (a) evaluate the analytical performance of urinary biochemical analytes across five laboratories, (b) design risk‐based statistical quality control (SQC) strategies, and (c) formulate improvement measures for each of the analytes when needed.MethodsInternal quality control (IQC) and external quality assessment (EQA) data for urinary biochemical analytes were collected from five laboratories, and the sigma value of each analyte was calculated based on coefficients of variation, bias, and total allowable error (TEa). Normalized sigma method decision charts for these urinary biochemical analytes were then generated. Risk‐based SQC strategies and improvement measures were formulated for each laboratory according to the flowchart of Westgard sigma rules, including run sizes and the quality goal index (QGI).ResultsSigma values of urinary biochemical analytes were significantly different at different quality control levels. Although identical detection platforms with matching reagents were used, differences in these analytes were also observed between laboratories. Risk‐based SQC strategies for urinary biochemical analytes were formulated based on the flowchart of Westgard sigma rules, including run size and analytical performance. Appropriate improvement measures were implemented for urinary biochemical analytes with analytical performance lower than six sigma according to the QGI calculation.ConclusionsIn multilocation laboratory systems, a six sigma model is an excellent quality management tool and can quantitatively evaluate analytical performance and guide risk‐based SQC strategy development and improvement measure implementation.     

Multicentre evaluation of an enzymatic method for creatinine determination using a sensitive colour reagent

A new enzymatic colorimetric method for the determination of creatinine in serum and urine (Creatinine PAP, Cat. No. 839434 and 836885, Boehringer Mannheim GmbH, Mannheim, FRG) was evaluated in 16 clinical chemistry laboratories and the manufacturer's testing laboratory. The test is based on the enzymatic degradation of creatinine and its reaction products by creatininase, creatinase and sarcosine oxidase. The H2O2 produced by the oxidation of sarcosine is determined using a modified Trinder reaction. The test can be carried out either manually or in mechanized analysers which enable the pipetting of a starter reagent to be made. The following results were obtained: Depending on the analyte concentration (range 40 to 1240 mumol/l), medians for the coefficients of variation were: 4.6-0.9% within-run and 6.4-2.8% between-day. At 546 nm the linear measuring range extended from 13 mumol/l (detection limit) to 1780 mumol/l, at 510 nm from 9 to 890 mumol/l. Recoveries in aqueous and human serum based standards as well as method comparisons with Fuller's earth methods and an enzymatic UV test indicate a high accuracy of this new enzymatic method in serum and urine. No interference was observed with haemolysed and lipaemic sera. This also applied to anticoagulants and to 36 drugs at therapeutic concentrations, with the exception of calcium dobesilate, which led to decreased values. Icteric samples containing 120-310 mumol/l bilirubin invariably led to decreased creatinine values (10-50 mumol/l lower). In a collaborative study substantially better interlaboratory agreement was observed with the new colorimetric enzymatic test than with the comparison methods (enzymatic UV test and various Jaffe procedures). In conclusion, this new enzymatic colorimetric test permits a precise and specific determination of creatinine in serum and urine. It makes a considerable contribution to improving the interlaboratory comparability of creatinine determinations and is suitable for routine use.     

Comparison between IDMS-traceable Jaffe and enzymatic creatinine assays for estimation of glomerular filtration rate by the CKD-EPI equation in healthy and diabetic subjects

Objectives

The aim of this paper was to compare the agreement between creatinine measured by Jaffe and enzymatic methods and their putative influence on eGFR as calculated by the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation in healthy and diabetic individuals.

Design and methods

Cross-sectional study conducted in 123 adult southern Brazilians with GFR > 60 mL/min/1.73 m² (53 patients with type 2 diabetes, 70 healthy volunteers). Mean age was 49 ± 16 years (range of 19–86). Most were female (55%) and white (83%). Creatinine was measured by a traceable Jaffe method (Modular P, Roche Diagnostic) and by an enzymatic method (CREA plus, Roche/Hitachi 917). GFR was measured by the ⁵¹Cr-EDTA single-injection method.

Results

Serum creatinine measured by the Jaffe and enzymatic methods was similar in healthy subjects (0.79 ± 0.16 vs. 0.79 ± 0.15 mg/dL, respectively, P = 0.76), and diabetic patients (0.96 ± 0.22 vs. 0.92 ± 0.29 mg/dL, respectively, P = 0.17). However, the correlation between the two methods was higher in the healthy group (r = 0.90 vs. 0.76, P < 0.001). The difference between Jaffe creatinine and enzymatic creatinine was < 10% in 63% of cases in the healthy group and 40% of cases in the diabetes group (P = 0.018). In the subset of patients with diabetes, eGFR based on enzymatic assay results showed better agreement with measured GFR than did eGFR based on Jaffe results.

Conclusion

Jaffe and enzymatic creatinine methods show adequate agreement in healthy subjects, but in the presence of diabetes, the enzymatic method performed slightly better.     

Deproteinization of serum: another best approach to eliminate all forms of bilirubin interference on serum creatinine by the kinetic Jaffe reaction

The negative interference of conjugated, unconjugated, and delta bilirubin on patient serum creatinine determined by the kinetic Jaffe reaction is the unresolved problem. We compared bilirubin interference on thirty patients' serum creatinine obtained from four analyzers, with and without deprotenization before the Jaffe reaction, to the Vitros dry enzymatic method. We found significant negative interference from bilirubin on serum creatinine in all samples directly applied to four wet chemical methods, except the one incorporated with serum blank rate. The negative interferences linearly related to bilirubin concentration. However, bilirubin did not interfere on serum creatinine obtained from all wet chemical methods incorporated with deproteinization process before the reaction. We conclude that deproteinized serum before the reaction is the best approach to eliminate all forms of bilirubin interference on serum creatinine determined by the kinetic Jaffe reaction.     

Use of robust ZB and ZW to evaluate proficiency testing data

BackgroundIn PT program, mean is conventionally used as the target after deletion of values which exceed the mean ± 3SD. This computation fails if there are some outliers.MethodsCreatinine data were divided into Jaffe and enzymatic method groups in accordance with the analytical method used. The results tested by both methods were compared. The normality of standardized sum and difference was tested. The outliers in these data were deleted. The trimmed data were tested for normality. The performance of laboratories was assessed using ZB and ZW, whose values were considered acceptable when |ZB| or |ZW|≤2, questionable when 2<|ZB|<3 or 2<|ZW|<3 and unacceptable when |ZB| or |ZW|≥3.ResultsThe results tested using Jaffe and enzymatic methods were not comparable. The data of standardized sum and difference were not normally distributed. When the outliers in these data were removed, the trimmed data were normally distributed. In Jaffe group, the acceptable rates of between and within laboratories respectively were 90.2% and 86.0%. In enzymatic group, the acceptable rates of between and within laboratories respectively were 82.6% and 82.4%.ConclusionIt was reasonable to choose robust ZB and ZW as assessment indexes because robust z-scores were less influenced by outliers.     

重庆市三甲医院临床生物化学常规项目正确度与精密度调查

目的调查重庆市三甲医院临床生物化学常规项目正确度及精密度。方法用参考方法为新鲜冰冻血清样品赋值,并发送给重庆市各个三甲医院临床实验室检测,分析和评估正确度通过率及精密度。结果 33家参加实验室肌酐、总蛋白、总胆红素、尿酸、葡萄糖等项目的正确度通过率低于50%;封闭检测系统中尿酸的正确度通过率(33%)小于开放检测系统(非原厂检测系统,79%,P=0.033);开放检测系统中,校准品与试剂品牌一致模式肌酐正确度通过率高于不一致模式(P=0.014);总胆红素和尿素各有1个水平封闭检测系统精密度高于开放检测系统(T-Bil,P=0.043;Urea,P=0.031)。结论重庆市三甲医院临床生物化学常规项目正确度均有待进一步提高;开放检测系统正确度、精密度与封闭系统无明显差距,某些项目性能超过封闭检测系统。     

Exogenous interferences with Jaffe creatinine assays: addition of sodium dodecyl sulfate to reagent eliminates bilirubin and total protein interference with Jaffe methods

Background: The study evaluated the impact of interferences on the analytical specificity of three commercial and commonly used creatinine methods (two Jaffe and one enzymatic). Methods: Manufacturer creatinine methods plus modified methods were tested with the following interferences: spiking serum with bilirubin, albumin, glucose, hemoglobin and lipid, and patient sera with maximum concentrations of bilirubin, 1,090 µmol/l and protein, 117.8 g/l. Results: Hemoglobin, 7.5 g/l and lipaemic with triglyceride concentration of 6.27 mmol/l, did not interfere with all assays. Glucose >33.3 mmol/l increased creatinine recovery for Dimension method. Samples spiked with bilirubin imparted a negative bias for Dimension and Architect methods but imparted a positive bias for Vitros assay. However, using patient sera, negative bias with bilirubin was found for all methods, from which Architect method gave the highest effect (R²=0.861), followed by Vitros (R²=0.239) and Dimension (R²=0.163). Protein provided the positive bias for all creatinine measurements that increased with increasing concentration (R² ranging from 0.104 to 0.182, P<0.0001). Addition of sodium dodecyl sulfate (SDS) in alkaline‐picrate reagent reduced the effect of bilirubin and protein for kinetic Jaffe method. Although adding potassium ferricyanide was well effective for eliminating negative interference of bilirubin, it was prone to interference from protein. Conclusions: Endogenous interferences continue to plague creatinine accuracy measurement in both Jaffe and enzymatic methods, and consequentially the estimated glomerular filtration rate. The addition of SDS to the alkaline‐pirate reagent was shown to be effective in reducing bilirubin and protein interferences. J. Clin. Lab. Anal. 24:123–133, 2010. © 2009 Wiley‐Liss, Inc.     

CALIPER paediatric reference intervals for the urea creatinine ratio in healthy children & adolescents

BackgroundThe urea creatinine ratio (UCR) is important in the clinical assessment of several medical conditions, including acute kidney injury and gastrointestinal bleeding. However, accurate and robust paediatric reference intervals (RIs) for this ratio have not been well established. Here, we determined age- and sex-specific discrete and continuous RIs for UCR in the Canadian Laboratory Initiative on Paediatric Reference Intervals (CALIPER) cohort of healthy children and adolescents for the first time.MethodsUCR was calculated for approximately 1030 CALIPER participants using retrospective urea and creatinine (both Jaffe and enzymatic methods) normative data. Partitions were determined using the Harris & Boyd statistical method. Discrete RIs were established in accordance with the Clinical and Laboratory Standards Institute (CLSI) guidelines. Continuous RIs were established using nonparametric quantile regression.ResultsSeveral age- and sex-specific partitions were necessary to capture dynamic physiological trends associated with this ratio throughout childhood and adolescence, highlighting the benefit of continuous RI establishment. Established UCR RIs also demonstrated marked differences between Jaffe and enzymatic assay methods.ConclusionOur results clearly demonstrate the critical need for RI stratification by important covariates such as age, sex, and creatinine assay methodology for paediatric UCR test result interpretation. These data contribute to our understanding of normative UCR values in childhood and adolescence and can be expected to improve paediatric test result interpretation in clinical laboratories that report this ratio.     

Compensating for the influence of total serum protein in the Schwartz formula

Abstract Background: The Schwartz 2009 creatinine-based revised formula is the only pediatric GFR estimating formula, which is compatible with the recent global creatinine standardization. This formula is only applicable if enzymatic creatinine methods are used. We propose an equation, taking into account the relative bias caused by serum proteins to use Jaffe based creatinine data for GFR estimation. Methods: In a cohort study of 100 pediatric patients, serum creatinine was measured using a kinetic rate-blanked Jaffe assay (modified kinetic alkaline picrate method), a kinetic rate-blanked Jaffe compensated assay for reactive proteins and an enzymatic assay (creatinine plus method). Serum total protein, albumin, urea, uric acid and total bilirubin were measured with the use of commercial agents. Results: The difference in serum creatinine between the enzymatic method and the compensated Jaffe method was mainly dependent on the total protein concentration in serum (r2=0.61, p<0.001). After applying the proposed protein correction, corrected compensated Jaffe results and creatinine clearance values became interchangeable with enzymatic serum creatinine results (r2=0.99, p<0.001; Deming regression: slope: 0.9787, intercept: -0.351) and with the newly proposed Schwartz formula, respectively (r2=0.99, p<0.001; Deming regression: slope 1.004, intercept: 2.16). Conclusions: In this study, we demonstrated the usability of the alkaline picrate method in the Schwartz formula, taking into account the relative bias caused by serum proteins.     

应用西格玛进行血清ALT,Cr,Glu检测项目的性能验证

目的 应用西格玛指标评价临床生化检验性能,了解广东省计划生育系统各级计划生育机构临床生化的检验质量现状,以其发现问题,促进质量提高.方法 通过向广东省19家计划生育机构实验室发放相同批号质控品,进行丙氨酸氨基转移酶（ALT）、肌酐（Cr）、血糖（Glu）项目的室内质控室间比对,计算各实验室室内质控结果,剔除离群值后的均值（x）、标准差（s）、室内变异系数（CV）、偏倚（bias）、西格玛（σ）值和质量目标指数（QGI）.结果 ALT,Cr和Glu大于6σ检测性能的实验室分别占16.68％,17.65％和35.29％;3≤σ＜6检测性能的实验室分别占44.44％,29.41％和35.29％.77％以上的实验室在检测ALT,Cr和Glu项目需从精密度和（或）正确度进行改进.结论 广东省计划生育机构实验室临床生化的检验性能有待提高,应用6σ评价室内质控室间比对,能将实验室的检测性能定量化,有助于检验质量的持续改进.     

利用稳健Z比分数评价肌酐能力验证的数据

目的 利用稳健Z比分数评价肌酐能力验证的数据.方法 肌酐数据来自2009年卫生部临床检验中心3次能力验证常规化学检测项目,分别有1 179、1169和1 168家实验室参加.按照检测方法的不同将肌酐能力验证的数据分为苦味酸组和酶组.利用Mann-Whitney检验作苦味酸法和酶法检测结果的可比性分析.利用四分位值建立的TUKEY区间剔除离群值.利用单样本Kolmogorov-Smirnov检验作原始数据和剔除离群值后数据的正态性分析.利用稳健Z比分数评价检测结果.Z比分数绝对值≤2的检测结果评价为满意值,2＜Z比分数绝对值＜3之间的检测结果评价为可疑值,Z比分数绝对值≥3的检测结果评价为不满意值.结果 苦味酸法和酶法的检测数据大部分(86.7％)不可比.所有研究组的原始数据是非正态分布,剔除离群值后,73.3％的数据是正态分布.2009年3次能力验证苦味酸组的满意率分别是89.8％ (495/551)、87.2％( 468/537)和89.5％ (476/532);不满意率分别是3.3％( 18/551)、6.5％ (35/537)和4.5％ (24/532).酶组的满意率分别是88.8％( 558/628)、89.3％( 564/632)和88.1％(560/636);不满意率分别是5.6％( 35/628)、5.2％ (33/632)和6.6％ (42/636).结论 选择稳健Z比分数作为能力验证的评价指标是合理的,避免了离群值对评价结果的影响.     

酶法与碱性苦味酸法测定肌酐清除值的差异情况研究

目的研究酶法和碱性苦味酸法测定肌酐清除值(CrCl)的差异,探讨酶法CrCl采用国外参考区间是否合适。方法分别用肌氨酸氧化酶法(简称酶法)和碱性苦味酸速率法(简称苦味酸法)测定266名患者的血肌酐、尿肌酐以及CrCl,并以苦味酸法CrCl水平分为4组,第1~4组CrCl分别为<25、26~50、51~80和>81 mL/min。分析两法测定血肌酐、尿肌酐和CrCl结果的差异以及各组两法差异的变化。结果酶法血肌酐值和尿肌酐值低于苦味酸法(P<0.001),酶法CrCl除第1组外均高于苦味酸法(P<0.001)。第1组两法血肌酐相对差值较小,且与两法尿肌酐相对差值接近,使CrCl在两法间无差异;第2~4组血肌酐相对差值逐渐增大,尿肌酐相对差值基本不变,导致CrCl在两法间出现差异且差异越来越大(P<0.001)。结论CrCl<25 mL/min时,两法CrCl没有差异;CrCl>26 mL/min时,两法CrCl出现差异且差值逐渐增大;CrCl正常组两法差值很大,酶法CrCl采用国外参考区间不合适。