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also known as method comparison.   This is the CAP checklist item:

**NEW**       04/21/2014


Comparability of Instruments/Methods

Phase II


If the laboratory uses more than one nonwaived instrument/method to test for a given analyte, the instruments/methods are checked against each other at least twice a year for comparability of results.

NOTE:  This requirement applies to tests performed on the same or different instrument makes/models or by different methods.  The purpose of the requirement is to evaluate the relationship between test results using different methodologies, instruments, or testing sites. This comparison is required only for nonwaived instruments/methods accredited under a single CAP number.  The laboratory must establish a written procedure for this check that includes acceptance criteria.  This requirement is not applicable to calculated parameters.

Quality control data may be used for this comparison for tests performed on the same instrument platform, with both control materials and reagents of the same manufacturer and lot number.

Otherwise, the use of human samples, rather than stabilized commercial controls, is preferred to avoid potential matrix effects. The use of pooled patient samples is acceptable since there is no change in matrix. In cases when availability or pre-analytical stability of patient/client specimens is a limiting factor, alternative protocols based on QC or reference materials may be necessary but the materials used should be validated (when applicable) to have the same response as fresh human samples for the instruments/methods involved.

This requirement only applies when the instruments/reagents are producing the same reportable result. For example, some laboratories may use multiple aPTT reagents with variable sensitivity to the lupus anticoagulant. If these are defined as separate tests, then this requirement does not apply unless each type of aPTT test is performed on more than one analyzer.

For Microbiology testing, this requirement applies when two instruments (same or different manufacturers) are used to detect the same analyte. Two or more detectors or incubation cells connected to a single data collection, analysis and reporting computer need not be considered separate systems (e.g. multiple incubation and monitoring cells in a continuous monitoring blood culture instrument, two identical blood culture instruments connected to a single computer system, or multiple thermocycler cells in a real time polymerase chain reaction instrument). This checklist requirement does not apply to multiple analytical methods (e.g. antigen typing versus culture or detection of DNA versus a biochemical characteristic) designed to detect the same analyte.

Evidence of Compliance:

       Written procedure for performing instrument/method comparison AND

       Records of comparability studies reflecting performance at least twice per year with appropriate specimen types




Department of Health and Human Services, Centers for Medicare and Medicaid Services. Medicare, Medicaid and CLIA programs; CLIA fee collection; correction and final rule. Fed Register. 2003(Jan 24):5236 [42CFR493.1281(a)]


Podczasy JJ, et al. Clinical evaluation of the Accu-Chek Advantage blood glucose monitoring system. Lab Med. 1997;28:462-466


Ross JW, et al. The accuracy of laboratory measurements in clinical chemistry: a study of eleven analytes in the College of American Pathologists Chemistry Survey with fresh frozen serum, definitive methods and reference methods. Arch Pathol Lab Med. 1998;122:587-608


Miller WG, Myers GL, Ashwood ER, et al. State of the Art in Trueness and Inter-Laboratory Harmonization for 10 Analytes in General Clinical Chemistry. Arch Pathol Lab Med 2008;132:838-846


Clinical and Laboratory Standards Institute. Verification of Comparability of Patient Results within One Healthcare System: Approved Guideline (Interim Revision). CLSI Document EP31-A-IR. Clinical and Laboratory Standards Institute, Wayne, PA; 2012.


Miller WG, Erek A, Cunningham TD, et al. Commutability limitations influence quality control results with different reagent lots. Clin Chem. 2011;57:76-83



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  • 5 months later...

We have a couple of different ways we do it depending on the test.  We only do 5 patient samples spanning the range for most assays.  ACT's and Hepcon tests we use QC samples on each device (excluding iSTAT ACT's which we use the 6 month internal simulator as a comparison of all "readers" and then use a single device to test against the Hepcon with a patient sample).  For PT/INR's, we review monthly any samples run POCT and in the core lab within 30 minutes as our correlation.

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  • 1 year later...

For correlation studies I only do 5-10 samples. I make sure to cover the range of values for each. For example the samples I run for our urine analyzers I try to have samples that are positive for glucose and bilirubin. I also make sure that the Specific Gravity covers a wide range as well as the pH. This helps me to be sure the refractometer and manual pH results also are covering the low, normal and high ranges. Our Joint Commission inspection this year was fine with that.



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On 4/6/2020 at 8:46 AM, Jparker said:

What if you only have one instrument at your clinic and have a sister clinic and main hospital. All have different cap numbers. Do you need to do instrument correlations? 

No - if they have different CLIA numbers they are considered different labs and comparison is not required between labs. However, some believe it is good practice to perform correlations between sites, but not required. 

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