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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Typically, there is no way to estimate the uncertainty of the “assayed” values, which is needed to determine if the calculated bias is statistically significant.

Similarly the within-laboratory precision is estimated by measuring a sample 20 times over multiple days.

Evaluating Assay Precision

Summing the square of the differences gives a total of 0. 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 internal quality control.

Use of these materials is important in establishing the traceability of measurement procedures.

CLSI document EPA2 describes the protocols that should be undertaken by the user to verify precision claims by a manufacturer.

If the estimated bias is less than allowable bias, the bias is acceptable. Finally, we can calculate the total csli within-laboratory SD s l using the equation:.

Guest Essay

Care must be taken in knowing which term is being referred to. 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. Open in a separate window.

For n measurements we have:. The following example relates to the verification z2 performance of calcium according to EPA2 using a five day protocol. The figure of 5.


Various materials may be used to complete the assessment with either protocol. 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.

Calculation of the verification interval would be complicated, but the committee cli it greatly by clei 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. 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.

Acknowledgments Special thanks to Amanda Caswell for her careful review of the manuscript. Linnet K, Boyd JC.

Here’s a brief description of the protocol. These include pooled patient samples, quality control material, or commercial standard material with known values. Journal List Clin Biochem Rev v. 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 dp15 obtained under identical conditions.

Using the values from our example the mean of all the results is 1. If the user is interested in estimating bias relative to the peer group for proficiency testing, and wants to estimate how the measurement procedure will perform well on proficiency testing, a22 testing materials with peer group values for clzi measurement procedure being evaluated are appropriate.

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

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.


The next step is to calculate the variance for the daily means s b 2 using the equation. If the calculated standard deviation is less than the verification limit, it is not statistically significantly larger than the published standard deviation, and the user has verified the published precision. The EPA2 protocol is similar except that the experiment is undertaken with three replicates over five days for at least two levels.

Sometimes the calculated standard deviations may exceed the published values, and yet the true standard deviations are less than the published values. ISSN — 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.

The repeatability and within-laboratory standard deviations are then compared to the claimed or published standard deviations.

CLSI EPA3: verification of precision and estimation of bias – Westgard

It may be especially useful when patient samples are difficult to obtain for a traditional comparison of methods experiment. The essentials to accomplish this were present in EP15 through all of its previous versions, but they cpsi refined and combined in EPA3 to make a vlsi experiment.

For this, longer-term assessment is required. The choice of material depends on the purpose of the user in estimating the bias. The user must evaluate the estimated bias versus allowable bias. The assessment is performed on at least two levels, as precision can differ over the analytical range of an assay. T is best calculated in a spreadsheet and is given by:. EP15 first describes a precision verification experiment.