Quantitative Validation Overview

SMILE

Johns Hopkins University

Baltimore, MD USA

SMILE Linearity Requirements-Chemistry

Author: Validation Committee / Document Number: / Equ35-A-05
Effective (or Post) Date: / 23-Mar-11
Review History / Date of last review: / NA
Reviewed by: / Heidi Hanes
SMILE Comments: This document is provided as an example only. It must be revised to accurately reflect your lab’s specific processes and/or specific protocol requirements. Users are directed to countercheck facts when considering their use in other applications. If you have any questions contact your SMILE representative.
SMILE Linearity Requirements-Chemistry / Document Number / 230
Effective Date / 19 Dec 2008
Subject
Guidelines for performing linearity testing on a chemistry analyzer / Page / 1 of 1
Supersedes / New
Author(s) / Name, Title / Date
Mark Swartz, Heidi Hanes, Jo Shim, Penny Stevens, Anne Sholander / Dec 2008
Approved by / Name, Title / Date
SMILE Validation Committee / Dec 2008
Review History / Date of last review: / 11 Mar 2011
Reviewed by: / Anne Sholander
Revision History / Version # [0.0] / Revision Date [dd/mm/yy] / Description (notes)
1.1 / 03/11/11 / Updated to acceptability criteria to remove reference to “pass or fail”.

SMILE Chemistry Linearity Guidelines

A quantitative analytical method is said to be LINEAR when measured results from a series of sample solutions are directly proportional to the concentration or activity in the test specimens. This means that a straight line can be used to characterize the relationship between measured results and the concentrations or activity levels of an analyte for some stated range of analyte values.

I.  Linearity

A.  Sample Criteria

1.  A minimum of 5 samples that cover the reportable range of the method.

2.  When plotted, the values should ideally be equidistant from each other.

3.  Quality control, calibrators or commercial linearity standards should be used.

B.  Testing

1.  At a minimum, run each sample in duplicate.

2.  Data should be plotted immediately to identify and correct any outliers.

C.  Evaluation of data:

1.  Plot the data in regression analysis program. The SMILE Linearity spreadsheet (Appendix 1) performs all necessary calculations.

a.  Plot the known values of the standards on the X-axis

b.  Plot the mean of the measured values on the Y-axis.

c.  Calculate slope and intercept using linear regression. This can be done using the Excel SLOPE and INTERCEPT functions or from the website http://tools.westgard.com/cgi-bin/westgard/comp_calc.cgi?header=http:/www.westgard.com/images/headtoolkit.gif

d.  Using slope and intercept, calculate a predicted Y value for each X value.

e.  Plot the predicted Y values versus the corresponding known X values on the same graph mentioned in a and b above. Draw a straight line to connect all the predicted Y points on the graph.

f.  Subtract each measured Y value from the associated predicted Y value. This difference is the systematic error due to non-linearity.

g.  Compare that systematic error to 50% of the total error. The systematic error must be less than 50% of the total error.

2.  Alternatively, plot the data in EP Evaluator Linearity Module or similar regression analysis program. If using EP follow the steps below. (See Appendix 2 for an example EP Linearity Report).

a.  Under the Linearity parameters select Confirm Linearity.

b.  Enter the Allowable Total Error (TEa) concentration and percent. Refer to SMILE Chemistry TE Limits table (Appendix 3).

c.  Enter 50% for Systematic Error.

d.  Select edit and enter the assigned values of your standards.

e.  Enter each replicate of your test data.

D.  Acceptability criteria

The method is linear if the difference between the predicted Y value and the measured Y value is less than the allowable error for each specimen point.

II.  References

A.  GCLP Workshop and Workbook18-20 May 2008, Verification of Performance Specifications, pages 1-33.

B.  Clinical and Laboratory Standards Institute (CLSI). Evaluation of the Linearity of Quantitative Measurement Approved Guideline-Second Edition, CLSI document EP6-A (ISBN 1-56238-498-8) Clinical and Laboratory Standards Institutes, 940 West Valley Road, Suite 100, Wayne, Pennsylvania 19098-1898 USA, 2005.

C.  EP Evaluator Release 8, David G. Rhoads Associates Inc., www.dgrhoads.com.

D.  James O. Westgard, Online Validation Training, Westgard QC, Inc. www.westgard.com, Sections 9-Determining Reportable Range.

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