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Linearity and Calibration Verification FAQs 

Questions

What is Linearity?

What is Calibration Verification?

How often is Calibration Verification required?

What is Reportable Range?

What is new instrument performance validation?

What is Analytical Measurement Range (AMR)?

Our inspection checklist requires Analytical Measurement Range (AMR) validation, can LGC Maine Standards’ products be used for AMR validation?

Do I have to use the CAP Linearity Survey (LN) in order to meet the CAP requirements for Calibration Verification on the CAP Checklist?

My laboratory is inspected by JCAHO.  Can I use your VALIDATE® linearity and calibration verification products to meet the requirements for calibration verification?

Answers

What is Linearity? As defined by CLSI’s (formerly NCCLS) EP06-A guideline:

"Linearity - the ability (within a given range) to provide results that are directly proportional to the concentration {amount} of the analyte in the test sample; NOTES:  a)  Linearity typically refers to overall system response (i.e., the final analytical answer rather than the raw instrument output; b)  The linearity of a system is measured by testing levels of an analyte which are known by formulation or known relative to each other (not necessarily known absolutely); when the system results are plotted against these values, the degree to which the plotted curve conforms to a straight line is a measure of system linearity."

VALIDATE® products are designed to make your linearity testing as easy as possible.

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What is Calibration Verification? CLIA ’88 defines the term calibration verification.  The definition is provided in 42 CFR 493 in section 493.2.

“Calibration verification means the assaying of materials of known concentration in the same manner as patient samples to substantiate the instrument or test system’s calibration throughout the reportable range for patient test results.”

The CLIA regulations are located on the CDC internet site at the following location http://wwwn.cdc.gov/clia/Regulatory/default.aspx with the definitions found here http://www.gpo.gov/fdsys/pkg/CFR-2003-title42-vol3/xml/CFR-2003-title42-vol3-part493.xml#seqnum493.2.

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How often is Calibration Verification required? According to the CLIA regulation provided in 42 CFR 493 section 493.1255:

"(b) Perform and document calibration verification procedures:

(3)  At least once every 6 months and whenever any of the following occur:

(i)  A complete change of reagents for a procedure is introduced, unless the laboratory can demonstrate that changing reagent lot numbers does not affect the range used to report patient test results, and control values are not adversely affected by reagent lot number changes.(ii)  There is a major preventive maintenance or replacement of critical parts that may influence test performance.(iii)  Control material reflect an unusual trend or shift, or are outside of the laboratory’s acceptable limits, and other means of assessing and correcting unacceptable control values fail to identify and correct the problem.(iv)  The laboratory’s established schedule for verifying the reportable range for patient test results requires more frequent calibration verification.  These requirement are located on CDC internet site at: http://www.gpo.gov/fdsys/pkg/CFR-2003-title42-vol3/xml/CFR-2003-title42-vol3-part493.xml#seqnum493.1255.

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What is Reportable Range? CLIA ’88 uses the term reportable range. The definition is provided in 42 CFR 493 in section 493.2.

“Reportable range means the span of test result values over which the laboratory can establish or verify the accuracy of the instrument or test system measurement response.”

This definition is very similar to the definition of Analytical Measurement Range (AMR) used by CAP.  Use of the LGC Maine Standards products meets the requirements for reportable range validation and calibration verification.  LGC Maine Standards provides five levels and has multiple product configurations available to maximize the reportable range with no dilutions for many instrument systems available.

The CLIA regulations are located on the CDC internet site at the following location http://wwwn.cdc.gov/clia/Regulatory/default.aspx with the definitions found here http://www.gpo.gov/fdsys/pkg/CFR-2003-title42-vol3/xml/CFR-2003-title42-vol3-part493.xml#seqnum493.2.

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What is new instrument performance validation? CLIA ’88 requires new instrument performance validation.  The requirements are specified in 42 CFR 493 in section 493.1253 "Standard:  Establishment and verification of performance specifications".

For a new unmodified, FDA-cleared or approved test system brought into the lab after April 24, 2003, the standard requires the following:

"(b)(1)(i) Demonstrate that it can obtain performance specifications comparable to those established by the manufacturer for the following performance characteristics:

(A)  Accuracy.(B)  Precision.(C)  Reportable range of test results for the test system."

LGC Maine Standards' VALIDATE® products are excellent for this testing and allow you to maximize your reportable range with no dilutions.

The CLIA regulations are located on the CDC internet site at the following location http://wwwn.cdc.gov/clia/Regulatory/default.aspx.  Here is a link to Section 493.1253 http://www.gpo.gov/fdsys/pkg/CFR-2003-title42-vol3/xml/CFR-2003-title42-vol3-part493.xml#seqnum493.1253.

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What is Analytical Measurement Range (AMR)? The College of American Pathologists (CAP) uses Analytical Measurement Range (AMR) as part of their checklist for their Laboratory Accreditation Program.  AMR is used as part of the CAP checklists to satisfy the CLIA ’88 requirements for the term ‘calibration verification’.  CAP uses two terms – calibration verification and AMR validation – to identify the two distinct processes required.  Definitions from CAP are provided below.  Per the article below, AMR must be revalidated at least every six months.

From March 2003 CAP Today,

“Analytical measurement range validation:

The process of confirming that the assay system will correctly recover the concentration or activity of the analyte over the AMR.  The materials used for validation must be known to have matrix characteristics appropriate for the method.  The matrix of the sample – that is, the environment in which the sample is suspended or dissolved-may influence the measurement of the analyte.  In many cases, the method manufacturer will recommend suitable materials.  The test specimens must have analyte values that, at a minimum, are near the low, midpoint, and high values of the AMR.  Specimen target values can be established by comparison with peer group values for reference materials, by assignment of reference or comparative method values, and by dilution or admixture ratios of one or more specimens with known values.  Each laboratory must define limits for accepting or rejecting validation tests of the AMR.  The AMR must be revalidated at least every six months, at changes in major system components, and when a complete change in reagents for a procedure is introduced, unless the lab can demonstrate that changing reagent lot numbers does not affect the range used to report patient/client test results.  Routine reagent lot changes may not require AMR revalidation if they occur within the six-month interval.  The laboratory director should determine what constitutes a major system component change or a "complete" change in reagents that would require revalidation of the AMR.  Manufacturers’ instructions should be followed.”¹

“Calibration verification:

The process of confirming that the current calibration settings remain valid for a method.  If calibration verification confirms that the current calibration settings are valid, it is not necessary to perform a complete calibration or recalibration of the method.  Calibration verification can be accomplished in several ways.  If the method manufacturer provides a calibration validation or verification process, it should be followed.  Other techniques include (1) assay of the current method calibration materials as unknown specimens and determination that the correct target values are recovered, and (2) assay of matrix-appropriate materials with accurate target values that are specific for the method.  Materials for calibration verification must have a matrix appropriate for the clinical specimens assayed by that method and target values appropriate for the measurement system.  In general, routine control materials are not suitable for calibration verification, except in situations where the material is specifically designated by the method manufacturer as suitable for verification of the method's calibration process.”¹

1.  Southwick, Karen.  Language Barrier Falls With Checklist Change.CAP Today 2003;3.

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Our inspection checklist requires Analytical Measurement Range (AMR) validation, can LGC Maine Standards’ products be used for AMR validation? Yes, the use of the LGC Maine Standards products meets the requirements for AMR validation and also for calibration verification.  The CAP checklist, and CLIA ’88 regulations, require three points for AMR validation:  lowest, midpoint and highest values.  “’We [in the committee] prefer at least five,’ says Dr. Ashwood, ‘but CLIA says three,’ so the checklist question specifies three.”¹  LGC Maine Standards provides five levels and has multiple product configurations available to get as close as possible to the lowest and highest values for the many instrument systems available to maximize the AMR with no dilutions.

1.  Southwick, Karen.  Language Barrier Falls With Checklist Change.CAP Today 2003;3.

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Do I have to use the CAP Linearity Survey (LN) in order to meet the CAP requirements for Calibration Verification on the CAP Checklist? No, the CAP does not require mandatory use of the CAP LN Survey materials in order to satisfy the CAP accreditation program.

In May of 2006, LGC Maine Standards  received written confirmation from the CAP regarding this matter.  A copy of this correspondence is available for download here.

If laboratory users are interested in the position of the CAP on this matter, please feel free to contact CAP directly via e-mail (accred@cap.org).

LGC Maine Standards is confident that its products are uniquely suited to provide for linearity and calibration verification needs in today’s clinical laboratory.  Please contact us with any questions you may have on this issue.

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My laboratory is inspected by JCAHO.  Can I use your VALIDATE® linearity and calibration verification products to meet the requirements for calibration verification? Yes, VALIDATE® linearity and  calibration verification products can be used to meet the JCAHO requirements for calibration verification.  JCAHO calibration verification requirements are contained in Standard QC.1.170, which went into effect January 1, 2005.  These standards can be found on the Joint Commission internet site.  Highlights, from the standard QC.1.170, concerning linearity and calibration verification are as follows:

  • Reportable range should be tested during calibration verification, including at least a minimal value, a mid-point value and a maximum value.
  • Calibration verification should be performed at least once every 6 months and whenever the following occur:
    • A complete change of reagents is introduced, unless it is demonstrated that control values are not affected
    • There is major preventive maintenance or replacement of critical parts
    • Control results indicate that there may be a problem with the test system
    • There is an environmental change, including instrument relocation, as applicable
    • There is an instrument replacement

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