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3 In 1988, the CAP Instrumentation Resource Committee (IRC) began offering linearity surveys as a tool for evaluating linearity. ![]() In the absence of testing at the upper limit of the analytic measurement range, laboratories had to narrow the range with a subsequent increase in the frequency of sample dilutions. Prior to the availability of linearity survey programs, such as those provided by the College of American Pathologists (CAP Northfield, Ill) and Casco (Portland, Me), individual laboratories were forced to undergo the difficult task of saving specimens from patients with elevated results for testing at the upper limits of the analytic measurement range. As described in NCCLS E6-P2, this linear relationship is important to clinicians who rely on this linear relationship for easy interpolation of results. It is the straight-line relationship between points that is the focus of interest in linearity evaluation. California clinical laboratory license verification serial#For example, testing serial dilutions of a sample with an elevated value is an acceptable approach. 2 In contrast, one does not need to know the absolute concentration to perform a linearity evaluation, even though knowledge of such is helpful in establishing upper and lower limits. California clinical laboratory license verification verification#Calibration verification ensures accuracy and involves measuring analytes in calibrators or other samples of known values traceable to a reference method to confirm that the established relationship has remained stable. The Clinical Laboratory Improvement Amendments of 1998 2 define calibration as the process of testing an analytical method to establish a relationship between known concentrations of an analyte (calibrators) and the measured value, but makes no specifications about linearity. ![]() Some laboratory personnel mistake the requirement for calibration verification with that for evaluating linearity. Therefore, the curve of the instrument response, which can be parabolic or sigmoid-shaped, should not be confused with linearity between the measured value and the true value. The test results from this transformation should be linearly proportional to the true value of the analyte in the sample solutions ( Figure 1). The responses may be transformed using a 4-parameter logistic formula or other formula such as logit-log. In some assays, the instrument response versus concentration of sample solutions is not linear for example, competitive radioimmunoassays have a parabolic-shaped instrument response when plotted against concentration and a sigmoid-shaped curve when the response is plotted against the logarithm of the concentration. 1 The points at the upper and lower limits of the analytic measurement range that acceptably fit a straight line determine the linear range. California clinical laboratory license verification series#Handling linearity data in an objective manner will aid clinical laboratorians whose goal is to improve the quality of the tests they perform.Īccording to NCCLS EP6-A, a quantitative analytical method is said to be linear when the analyte recovery from a series of sample solutions (measured value) is linearly proportional to the actual concentration or content of the analyte (true value) in the sample solutions. Regression analysis, as developed as the polynomial method, is partly based on the experiences of the College of American Pathologists Instrumentation Resource Committee and has proved to be a robust statistical method.Ĭonclusions.-We provide general guidelines for handling non-linear results from a linearity evaluation. The lack-of-fit error and the 1986 NCCLS EP6-P G test are sensitive to imprecision and assume that the data are first order. Results.-Visual assessment, although simple, is subjective. We then evaluate the statistical methods for each procedure. ![]() Objective.-This article evaluates the concepts and importance of linearity evaluations for clinical tests.ĭesign.-We describe the theory and procedural steps of each linearity evaluation. Although an important part of quality control and method validation for clinical laboratories, linearity of clinical tests does not get the attention it deserves. Context.-Clinical laboratory assessment of test linearity is often limited to satisfying regulatory requirements rather than integrating this tool into the laboratory quality assurance program.
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