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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This is valuable when the user wishes to verify precision and to estimate bias relative to a peer group or target concentration. If the mean concentration from the user’s experiment is beyond the verification interval, statistically significant bias exists. Using the values from our example the mean of all the results is 1.

The only requirement is that the assigned value must be available. Similarly the within-laboratory precision is estimated by measuring a sample 20 times over multiple days.

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. Journal List Clin Biochem Rev v.

Evaluating Assay Precision

Xlsi 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. There is some variation in the terminology used but for the purposes of this discussion, repeatability, also known as within-run precision, is defined as the closeness of agreement between results of successive measurements obtained under identical conditions.


Calculation of the verification interval would be complicated, but the dp15 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, and the uncertainty of the target value. 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 clsk acceptability limits for internal quality control.

National Institute of Standards and Technology, or from the Joint Committee for Traceability in Laboratory Medicine, or from similar organizations may be xlsi if the user wishes to estimate the bias relative to the assigned concentrations of such materials.

Guest Essay

If an outlier is found the pair should be rejected and the cause investigated and resolved before repeating the run. Selection and analytical evaluation dlsi methods with statistical techniques.

The user must evaluate the estimated bias versus allowable bias. The width of the verification interval depends on the uncertainty of the target value of the reference material and the standard error of the calculated mean concentration from the experiment. A spreadsheet for assisting with the calculations described in this article is available from the AACB web-site.

First, users rarely have access to the measurement procedure used by the manufacturer or authors of a publication as the comparative method for the published bias.

If the calculated standard deviations are less than the published values, the user has verified the claim. National Center for Biotechnology InformationU. There were two problems with this approach.

Evaluating Assay Precision

If the mean concentration from the user’s experiment is within the verification interval, there is no statistically significant bias. Here’s a brief description of the protocol. Finally, we can calculate the total or within-laboratory SD s l using the equation:. Elsevier Saunders; St Louis: 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. Summing the square of the differences gives a total of 0.


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

EPA2 should be used to validate a method against user requirements, and is generally used by reagent and instrument suppliers to demonstrate the precision of their methods. Support Center Support Center. Tools, Technologies and Training for Healthcare Laboratories. It may be especially useful when patient samples are difficult to obtain for a traditional comparison of methods experiment.

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

Author information Clai and License information Disclaimer. The first replicate on day 1 is 2. This article has been cited by other articles in PMC. For a normal distribution the measure of imprecision is the standard deviation SD. User verification of performance for precision and trueness; approved guideline.