The EPA2 protocol from CLSI. • Uses control material with assigned concentration (e g from external quality control) or certified reference materials. We are pleased to have a guest essay explaining the latest in Method Verification , specifically the newest version of the CLSI guideline EP15 on Method. CLSI document EPA2 describes the protocols that should be undertaken by the user to verify precision claims by a manufacturer. Precision claims by a.
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When using quality control samples, these should be different to those used to ensure the instrument is in control at the time of the assessment. For this, longer-term assessment is required. For a normal distribution the measure of imprecision is the standard deviation SD. For example, if the true standard deviations were actually exactly equal to their claimed counterparts, the calculated standard deviations would exceed their published counterparts fifty percent of the time in verification experiments.
Finally, we can calculate the total or within-laboratory SD s w2 using the equation:.
Ep115 evaluating the precision of an assay, the trivial approach for estimating repeatability for any given level is to perform 20 replicate analyses in a single run on a single day.
The only requirement is that the assigned value must be available. No literary a in The Clinical Biochemist — Reviews is to be reproduced, stored in a retrieval system or transmitted in any form by electronic or mechanical means, photocopying or recording, without permission.
Here’s a brief description of the protocol. Patient samples, reference materials, proficiency rp15 samples, or control materials c,si be used as the test samples, provided there is sufficient sample material for testing each sample five times per run for five to seven runs. Repeatability Verification Value In order to compare the estimated repeatability to a claimed value we can calculate the critical or verification value using the equation: Elsevier Saunders; St Louis: It is generally assumed in the laboratory that the variation associated with repeated analysis will follow a normal distribution, also known as the Laplace-Gaussian or Gaussian distribution.
There should be at least one quality control QC cllsi in each run. Using the values from our example the mean of all the results is 1. Repeatability Repeatability is estimated using the equation below.
Patient samples or control materials which have been repeatedly assayed with a measurement procedure felt to be substantially equivalent to the measurement procedure being evaluated cclsi be appropriate if the user is interested in estimating bias relative to that measurement procedure.
Introduction Part of the process of verifying or validating a method to confirm that it is suitable for use is an assessment of precision.
If an outlier is found the pair should be rejected and the cause investigated and resolved before repeating the run. Tools, Technologies and Training for Healthcare Laboratories. The user needs access to software to do the ANOVA calculations, but they are available in Excel, Minitab, Analyze-it, and other software packages that do statistical calculations. If the measurement procedure’s imprecision reported in publications, such as the manufacturer’s stated imprecision, does not meet the criterion, the precision verification procedure described in EPA3 is not appropriate.
Summary When evaluating the precision of a method it is necessary to assess dp15 repeatability within-run and the total or within-laboratory precision. Within-Laboratory Precision Finally, we can calculate the total or within-laboratory SD s l using the equation: Precision claims by a manufacturer should be tested at at-least two levels, by running three replicates over five days. If the estimated bias is less than allowable bias, the bias is acceptable.
Alternatively one can use the variance, which is simply the square of the SD. Typically, there is no way to estimate the uncertainty of the “assayed” clis, which is needed to determine if the calculated bias is statistically significant. The figure of 5. Second, most manufacturers provide only regression statistics as the results of comparison experiments, and do not provide bias claims, so the user has to calculate the bias to be expected from the regression statistics provided and has little idea of the uncertainty of this estimated bias.
If this is true then using the principle of analysis of variance components:. Cli the calculated standard deviations are less than the published values, the user has verified the claim.
CLSI/NCCLS: EPA2. User verification of performance for precision and trueness – ScienceOpen
It may be especially useful when patient samples are difficult to obtain for a traditional comparison of methods experiment. Internationally recognized high order reference materials, such as clsk material from the U.
This could be useful, for example, if the intent of the experiment was to estimate the bias of one laboratory in a system relative to another, or to the mean of the laboratories in a system. Statements of opinion in AACB publications are those of the contributors. While the term precision relates to the concept of variation around a central value, imprecision is actually what is measured. The first step is to calculate the mean of the replicates for each day, then for each result subtract the mean for that day and square the resultant value.
Author information Copyright and License information Disclaimer. Linnet K, Boyd JC.
CLSI EPA3: verification of precision and estimation of bias – Westgard
Acknowledge Committee Members The EPA3 document development committee was team of experts who worked together well. Because the precision experiment has so many replicate measurements, collected over several days, results from the precision experiment may be used to make a reliable estimate of the bias of the measurement procedure relative to the assigned target values of the sample materials used in the experiment.
Acknowledgments Special thanks to Amanda Caswell for her careful review of the manuscript. This is its fourth iteration, and although it retains much of its original approach, there were some significant changes in the A3 version. If QC material is being used for the precision assessment, it should be different to that used to control the assay.
The most significant change is the creation of a relatively simple experiment that gives reliable estimates of a measurement procedure’s imprecision and its bias.