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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Estimation of Repeatability and Within-Laboratory Precision The following example relates to the verification of performance of calcium according to EPA2 using a five day protocol. No literary matter in The Clinical Biochemist — Reviews is to cksi reproduced, stored in ep5 retrieval system or transmitted in any form by electronic or mechanical means, photocopying or recording, without permission.

Journal List Clin Biochem Rev v. Introduction Part of the process of verifying or validating a method to confirm that it is suitable for use is an assessment of precision. For bias relative to the quality control peer group, quality control materials with peer group values for the measurement procedure are appropriate. On day 1 the mean of the three replicates was 1.

Evaluating Assay Precision

Using the values from our example the mean of all the results is 1. Sometimes the manufacturer identifies clzi comparative measurement procedure only generically.

Patient samples, reference materials, proficiency testing samples, or control materials may 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. T is best calculated in a spreadsheet and is given by:.

Author information Copyright and License information Disclaimer. Care must be taken in knowing which term is being referred to. Tools, Technologies and Training for Healthcare Laboratories.

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: There were two problems with this approach.

The reader is referred to the CLSI documents for details. Cli may be especially useful when patient samples are difficult to obtain for a traditional comparison of methods experiment. National Institute of Standards and Technology, or from the Joint Committee for Traceability in Laboratory Medicine, or from similar organizations may be appropriate if the user wishes to estimate the bias relative to the assigned concentrations of such materials.


CLSI/NCCLS: EPA2. User verification of performance for precision and trueness – ScienceOpen

Requests to do so should be addressed to the Editor. The document includes tables to simplify the calculation of the verification limit. The experiment produces at least 25 replicates collected over at least 5 days for each sample material.

Instead total precision within a laboratory within-laboratory precision will be assessed. Calculation of the verification interval would be complicated, but the committee simplified it greatly by providing tables for the difficult-to-calculate quantities based on the number of replicate measurements per run, the number of runs, clai the uncertainty of the target value. Open in a separate window. If the calculated standard deviations are less than the published values, the user has verified the claim.

The next step is to calculate the variance for the daily means s b 2 using the equation. 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.

When undertaking the assessment the data must be assessed for outliers, which are considered to be present if the absolute difference between replicates exceeds 5.

This article has been cited by other articles in PMC. In order to compare the estimated repeatability to a claimed value we can calculate the critical or verification value using the equation:. The figure of 5. Unfortunately this approach is insufficient, as it tends to under-estimate repeatability, as the operating conditions in effect at the time may not reflect usual operating parameters. The first step is to calculate the mean of the replicates for each day, then for each result subtract the clxi for that day and square the resultant value.

If the estimated bias exceeds allowable bias, it is not acceptable.

Precision should be tested with two or more sample materials at different medical decision point concentrations. Verification of Precision EP15 first describes a precision verification experiment.

User verification of performance for precision and trueness; approved guideline. As the period of assessment is quite short, the total SD or within-laboratory SD derived from these experiments should not generally be used to define acceptability limits for clsl quality control.


The assessment is performed on at least two levels, as precision can differ over the analytical range of an assay. The EPA3 document development committee was team of experts who worked together well. 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.

Two or more appropriate materials should be tested in the precision experiment. If this is true then using the principle of analysis of variance components:. Lcsi is its fourth iteration, and although it retains much of its original approach, there were some significant changes in the A3 version. Australasian Association of Clinical Biochemists Website.

Various materials may be used to complete the assessment with either protocol. Clinical and Laboratory Standards Institute.

Guest Essay

This is valuable when the user wishes to verify precision and to estimate bias relative to a peer group or target concentration. There should be at least one quality control QC sample in each run. If QC material is being used for the precision assessment, it should be different to that used to control the assay. 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.

Reproducibility is at the other extreme and refers to the closeness of agreement between results of successive measurements obtained under changed conditions time, operators, calibrators, reagents, and laboratory. Thus the variance of the daily means is:. If the user is evaluating a procedure for which there are manufacturer’s precision claims, or published precision results, that were developed using CLSI EP5, the user can verify the published precision in an experiment lasting as few as five days.

National Center for Biotechnology InformationU. However, for a method developed in-house a higher level of proof is required to validate the method, in which case EPA2 would be the appropriate guideline to use.