Validity of the Consensus Mean as the Target Value for a Small External Quality Assessment Scheme

1985 ◽  
Vol 22 (3) ◽  
pp. 283-290 ◽  
Author(s):  
R J Georges
Keyword(s):  
Quality Assessment ◽  
Coefficient Of Variation ◽  
Analytical Methods ◽  
Close Agreement ◽  
External Quality Assessment ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Mean Values ◽  
Consensus Mean ◽  
The Mean

Data from 2 years' operation of an External Quality Assessment Scheme covering 14 analytes and with some 60 participants is presented. Following the trimming of discrepant results and statistical ‘outliers' (outside the range of ±3 SD from the mean), there was generally close agreement between consensus mean values for a specimen analysed on different occasions, by different groups of laboratories, or when using different analytical methods. An improvement in performance, indicated by a reduction in the average inter-laboratory coefficient of variation was found for 11 of the 14 analytes over the 2-year period.

What can be achieved in an external quality-assessment scheme with a small number of participants: four years of experience with thyroid-related tests in Israel

1991 ◽  
Vol 37 (8) ◽  
pp. 1432-1436
Author(s):  
L Kahana ◽  
H Yechieli
Keyword(s):  
Quality Assessment ◽  
External Quality Assessment ◽  
First Year ◽  
Considerable Decrease ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Related Function ◽  
Scheme Design ◽  
Individual Laboratory ◽  
Consensus Mean

Abstract The Israel External Quality-Assessment scheme (EQAS) provided service from 1985 to 1989, primarily to laboratories in Israel. Participation was voluntary and confidential, and involved 30-35 laboratories performing thyroid-related function tests. Scheme design included 36 human serum specimens distributed to the participants at the beginning of each year. For 12 months, three specimens were analyzed each month and the results were reported to EQAS on pre-agreed dates. Monthly reports sent by EQAS to participants after analysis of the results included the overall consensus mean used as target value, between-laboratory agreement, individual laboratory bias, and recovery data. The overall consensus mean calculated as all-laboratory trimmed mean was validated by reproducibility and recovery studies. Samples with undetectable concentrations of thyrotropin (TSH), obtained from patients proven thyrotoxic, were used to validate measurement of very low TSH concentrations. During the scheme, liquid serum was found superior to lyophilized specimens for distribution to the participants. The scheme helped stimulate major improvements in between-laboratory agreement, especially for low TSH concentrations, with CVs decreasing from 180% in the first year to 20% in the fourth year. Each laboratory's performance also improved as judged by the median bias and variability of bias and by the considerable decrease in the number of laboratories with unacceptable performance for all tests. Method-related differences in performance were observed despite the small number of participants. Better methods, e.g., a radioimmunometric method for TSH, were detected and adopted by the participants, with concomitant improvement in performance. Transfer to analog procedures for free thyroxin, in addition to, but mostly instead of, thyroxin, was also documented, with no gain in analytical performance. Despite this being a small scheme, most of the goals achievable with a large scheme were realized.

scholarly journals Application of the Characteristic Function to Evaluate and Compare Analytical Variability in an External Quality Assessment Scheme for Serum Ethanol

2015 ◽  
Vol 61 (7) ◽  
pp. 948-954 ◽  
Author(s):  
Wim Coucke ◽  
Corine Charlier ◽  
Willy Lambert ◽  
Frank Martens ◽  
Hugo Neels ◽  
...  
Keyword(s):  
Characteristic Function ◽  
Quality Assessment ◽  
Analytical Methods ◽  
External Quality Assessment ◽  
Evaluation Process ◽  
Clinical Diagnostics ◽  
External Quality ◽  
Target Concentration ◽  
External Quality Assessment Scheme ◽  
Method Performance

Abstract BACKGROUND As a cornerstone of quality management in the laboratory, External Quality Assessment (EQA) schemes are used to assess laboratory and analytical method performance. The characteristic function is used to describe the relation between the target concentration and the EQA standard deviation, which is an essential part of the evaluation process. The characteristic function is also used to compare the variability of different analytical methods. METHODS We fitted the characteristic function to data from the Belgian External Quality Assessment program for serum ethanol. Data included results from headspace gas chromatography and the enzymatic methods of Abbott, Roche, Siemens, and Ortho-Clinical Diagnostics. We estimated the characteristic function with weighted nonlinear regression. By introducing dummy variables, we rewrote the original formula of the characteristic function to assess statistical inference for comparing the variability of the different analytical methods. RESULTS The characteristic function fitted the data precisely. Comparison between methods showed that there was little difference between the estimated variability for low concentrations, and that the increase in SD with increasing target concentration was slower for Abbott and Roche than for the other methods. CONCLUSIONS The characteristic function can successfully be introduced in clinical schemes, although its applicability to fit the data should always be assessed. Because of its easy parameterization, it can be used to assess differences in performance between analytical methods and to assess laboratory performance. The characteristic function also offers an alternative framework for coefficients of variation to describe variability of analytical methods.

Effect of Favourable Treatment of Samples on Indices of Performance in External Quality Assessment Schemes

1982 ◽  
Vol 19 (3) ◽  
pp. 171-175 ◽  
Author(s):  
Alan Geoffrey Rumley ◽  
Leslie Barry Roberts
Keyword(s):  
Quality Assessment ◽  
External Quality Assessment ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Mean Values

This study was carried out to examine the effect on performance, as assessed by external quality assessment schemes, of ( a) replicate analysis of external quality assessment samples, and positioning of external quality assessment samples immediately after the calibrants, and ( b) alteration of results on the basis of previous performance in order to bring them closer to the method mean values obtained from all laboratories participating in the external quality assessment scheme. Indices of performance were then compared with those obtained from our normal practice where external quality assessment samples were treated as patient samples. Using these methods we were unable to improve significantly our precision or league ranking based on precision over the six-month period of study. We were able to reduce our bias from method means but at the expense of making precision and league ranking worse.

Improvement of Coagulation Laboratory Practice in Thailand: The First-Year Experience of the National External Quality Assessment Scheme for Blood Coagulation

2009 ◽  
Vol 133 (1) ◽  
pp. 72-77
Author(s):  
Panutsaya Tientadakul ◽  
Nisarat Opartkiattikul ◽  
Wanida Wongtiraporn
Keyword(s):  
Quality Assessment ◽  
Blood Coagulation ◽  
Coefficient Of Variation ◽  
Partial Thromboplastin Time ◽  
External Quality Assessment ◽  
International Normalized Ratio ◽  
Activated Partial Thromboplastin Time ◽  
Laboratory Practice ◽  
External Quality ◽  
External Quality Assessment Scheme

Abstract Context.—In Thailand until 2005 there had been no external quality assessment scheme at the national level for blood coagulation tests. Only a few laboratories had an external quality assessment for these tests. In the year 2005, the Thailand National External Quality Assessment Scheme for Blood Coagulation was founded. Objectives.—To describe the establishment of the Thailand National External Quality Assessment Scheme for Blood Coagulation (including problems encountered and solutions), its progression and expansion, and the improvement of coagulation laboratory practice in Thailand during 2 trial surveys and 4 formal surveys conducted in the first 1;h1 years. Design.—Between 2005 and 2006, the external quality assessment samples for prothrombin time/international normalized ratio and activated partial thromboplastin time were distributed to the participants as well as the instructions and suggestions for the improvement of laboratory practice. From the data collected, the all-method coefficient of variation of the international normalized ratio and activated partial thromboplastin time was calculated for each survey. Results.—The number of participants increased during the first 1;h1 years that the surveys were conducted, from 109 to 127. Survey data demonstrate an improvement in response rate and an increase in the number of laboratories that determine their own reference ranges and repeat this for every change of reagent lot, using the appropriate anticoagulant. The increased precision of tests is indicated by the decrease of the all-method coefficient of variation of the international normalized ratio and activated partial thromboplastin time. Examples of individual laboratory improvement through feedback are also described. Conclusions.—The improvement of coagulation laboratory practice both through the instructions provided and liaison with participants was observed during the course of this scheme.

scholarly journals A design for external quality assessment for the analysis of thiopurine drugs: pitfalls and opportunities

2018 ◽  
Vol 56 (10) ◽  
pp. 1715-1721 ◽  
Author(s):  
Karen Robijns ◽  
Matthijs van Luin ◽  
Rob T.P. Jansen ◽  
Cees Neef ◽  
Daan J. Touw
Keyword(s):  
Quality Assessment ◽  
External Quality Assessment ◽  
Absolute Difference ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Mean Absolute Difference ◽  
Standard Operating ◽  
Pure Substances ◽  
The Mean ◽  
Control Samples

Abstract Background For the analysis of 6-thioguanine nucleotides (6-TGN) and 6-methylmercaptopurine ribonucleotides (6-MMPR), no external quality assessment scheme (EQAS) is currently available and no quality control samples can be made because of the absence of pure substances. An experimental design is tested to compare laboratory analytical results. Methods In this EQAS, participating laboratories were asked to select patient samples from their routine analysis and exchange these with a coupled laboratory. Because of large differences in results between laboratories, all standard operating procedures were reviewed, revealing that the origin of these differences could be in the method of hydrolysis and the preparation of calibrators. To investigate the contribution of the calibrators to these differences, one participating laboratory was asked to prepare a batch of calibrators to be shipped to the participating laboratories for analysis. Results Results for 6-TGN differed more between laboratories, compared with results for 6-MMPR. For 6-TGN and 6-MMPR 43% and 24% of the results, respectively, were out of the 80%–120% range. When correcting the results from the exchange of the patient samples with the results of the calibrators, the mean absolute difference for 6-TGN improved from 24.8% to 16.3% (p<0.001), while the results for 6-MMPR worsened from 17.3% to 20.0% (p=0.020). Conclusions This first EQAS for thiopurine drugs shows that there is a difference between laboratories in the analysis of 6-TGN, and to a lesser extent in the analysis of 6-MMPR. This difference for 6-TGN can partially be explained by the use of in-house-prepared calibrators that differ among the participants.

scholarly journals External Quality Assessment of Techniques for Assay of Serum Ethanol

1995 ◽  
Vol 32 (6) ◽  
pp. 540-544 ◽  
Author(s):  
J F Wilson ◽  
K Barnett
Keyword(s):  
Quality Assessment ◽  
External Quality Assessment ◽  
Headspace Analysis ◽  
Packed Columns ◽  
Negative Bias ◽  
External Quality ◽  
Variable Technique ◽  
External Quality Assessment Scheme ◽  
Consensus Mean ◽  
The Uk

Ethanol was assayed by an average of 200 participants in the UK National External Quality Assessment Scheme, in 26 samples of human serum containing 0·1% fluoride/oxalate and added ethanol from 0·2 to 4·5 g/L. Outliers greater than three standard deviations from the consensus mean for any sample were excluded. Data remaining were grouped by technique and the technique mean and standard deviation calculated. Inter-laboratory variation of 13 technique groups was assessed by the coefficient of variation of measurements and bias from the per cent difference of the technique mean from the target value. Gas chromatography (GC) with packed columns and Sigma alcohol dehydrogenase assay protocols that included a sample deproteinization step, showed better between-laboratory agreement but greater bias. The least variable techniques were headspace analysis with GC-packed columns, Kodak Ektachem, bioMérieux and DuPont aca assays. A significant negative bias was produced by Kodak Ektachem and a positive bias by the Lion alcometer which was the most variable technique.

Establishing an Accuracy Basis for the Vitamin D External Quality Assessment Scheme (DEQAS)

2017 ◽  
Vol 100 (5) ◽  
pp. 1277-1287 ◽  
Author(s):  
Carolyn Q Burdette ◽  
Johanna E Camara ◽  
Federica Nalin ◽  
Jeanita Pritchett ◽  
Lane C Sander ◽  
...  
Keyword(s):  
Vitamin D ◽  
Quality Assessment ◽  
External Quality Assessment ◽  
Measurement Procedure ◽  
Binding Assays ◽  
External Quality ◽  
External Quality Assessment Scheme ◽  
Hydroxyvitamin D ◽  
Target Values ◽  
High Concentrations

Abstract Until recently, the Vitamin D External Quality Assessment Scheme (DEQAS) assessed the performance of various assays for the determination of serum total 25-hydroxyvitamin D [25(OH)D] by using a consensus mean based on the all-laboratory trimmed mean (ALTM) of the approximately 1000 participants' results. Since October 2012, the National Institute of Standardsand Technology (NIST), as part of the Vitamin D Standardization Program, has participated in DEQAS by analyzing the quarterly serum sample sets using an isotope dilution LC-tandem MS (ID LC-MS/MS) reference measurement procedure to assign an accuracy-based target value for serum total 25(OH)D. NIST has analyzed90 DEQAS samples (18 exercises × 5 samples/exercise) to assign target values. The NIST-assigned values are compared with the ALTM and the biases assessed for various assays used by the participants, e.g., LC-MS/MS, HPLC, and several ligand-binding assays. The NIST-value assignment process and the resultsof the analyses of the 90 DEQAS samples are summarized. The absolute mean bias between the NIST-assignedvalues and the ALTM was 5.6%, with 10% of the samples having biases &gt;10%. Benefits of the accuracy-based target values are presented, including for sample sets with high concentrations of 25(OH)D2 and 3-epi-25(OH)D3.

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