My battle with Commutability part 4

Part 3 of this series is here.

The final version in this series is facilitated by a recent article. This article is written by three people, two of which are on the IFCC committee – hence there is traceability (Smiley).

The article provides a review of standardization and harmonization, which are essential in getting results from different labs to agree. I encourage people to read this well written review of standardization and harmonization.

Finally, this article discusses commutability and provides a figure showing three graphs. Each graph contains the results from measurement procedure 2 vs measurement procedure 1 for both clinical samples and reference materials. (I won’t show this figure due to copyright issues). The results are as follows:

Panel A shows clinical samples and reference materials on the same line – thus these reference materials are called commutable.

Panel B shows clinical samples with reference materials not the same line – thus these reference materials are called noncommutable.

Panel C shows the noncommutable reference materials from Panel B used as calibrators with the result that the clinical samples are offset and said to be inaccurate.

But this assumes that measurement procedure 1 is being used as a reference procedure. So even when there is no real reference method, often a method is chosen to be the reference method. And, the information in Panels A and B are equivalent. If one calibrates Panel A using its reference materials as calibrator, one gets accurate values, but one can still get accurate values in Panel B using its reference materials as calibrator, provided one offsets the calibrator values to make the patient samples come out right. Thus, Panels A and B have the same information.

To summarize, standardization and harmonization are essential for results to agree – commutability is not.

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