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D-dimer AMR and CRR

From Heather DeVries, Indiana University: Greetings George!
The labs within our system have been discussing our reportable range for D-dimers. Our vendor’s stated limit is beyond what calculates from our AMR and maximum dilution. We are debating changing our reportable range to what we calculate, and stop using the vendor’s limit so that we truly are within CAP regulations. What do other systems do? Would they choose to stay with the vendor’s limit and refer to them if questioned by CAP, or would they change to what calculates out mathematically? I can give specific numbers if this doesn’t make sense! Thanks, Heather

Thank you, Heather, it definitely seems you are doing the right thing, I will be interested in learning what our other participants are doing in this case.

To define, the reportable range (clinical reportable range, CRR, clinical measurement range, CMR) is the span of test result values over which the laboratory can establish or verify the accuracy of the instrument or test system measurement response, The CRR permits for diluting a specimen whose analyte result exceeds the analytical measurement range, assaying the dilution, and reporting the result after multiplying by the dilution factor. The analytical measurement range (AMR) is the span of test result values in which the results are proportional to the true concentration of the analyte in the sample or the range over which the test can be performed without modification. The AMR is determined locally and may match manufacturer-computed linearity or, as described by Ms. DeVries, may have narrower limits.

Comments (1)
Nov 22, 2016 10:09am

You cannot depend on the
You cannot depend on the instrument/reagent manufacturer’s claims for AMR. You must prove it for your laboratory. We use the limits established by linearity testing. If the test is linear to the highest value of a sample in the linearity test sample set, we use that as our AMR high limit. If we get a higher sample in a subsequent test set and it still is linear, we may adjust our upper limit of AMR.
At least two factors affect or limit the clinical measurement range (CMR), First is the maximum dilution that does not affect final test results. There are test results that are markedly affected by dilution because dilution alters the test matrix. Some tests do not allow dilution, and others (e. g., hCG) you can dilute almost infinitely. The second is the clinical importance of the test result. Where does clinical importance stop? Does it make any clinical relevance whether the enzyme measurement is 10,000 IU or 15,000 IU? The CMR is usually determined by the laboratory medical director, often in consultation with the physician groups most often affected.

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