SMILE
Johns Hopkins University
Baltimore, MD USA
SMILE Linearity Requirements-Chemistry
Author: Validation Committee
Review History
Document Number:
Equ35-A-05
Effective (or Post)
Date:
23-Mar-11
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
Page
1 of 1
Supersedes
New
Subject
Guidelines for performing linearity testing on a chemistry analyzer
Name, Title
Author(s)
Date
Mark Swartz, Heidi Hanes, Jo Shim, Penny
Stevens, Anne Sholander
Name, Title
Approved by
Date
SMILE Validation Committee
Date of last review:
Review History
Reviewed by:
Version # [0.0]
Revision
History
533576754
1.1
Revision Date
[dd/mm/yy]
03/11/11
Dec 2008
Dec 2008
11 Mar 2011
Anne Sholander
Description (notes)
Updated to acceptability criteria to remove reference to “pass or fail”.
Page 1 of 3
SMILE
Johns Hopkins University
Baltimore, MD USA
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/cgibin/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.
533576754
Page 2 of 3
SMILE
Johns Hopkins University
Baltimore, MD USA
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 190981898 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.
533576754
Page 3 of 3