This study was undertaken to evaluate the feasibility of using commercial control materials in a regional external quality assessment scheme (EQAS) for serum carcinoembryonic antigen (CEA) measurement. We have assessed the commutability of 12 commercial control materials using five automated immunochemical systems. We compared the intermethod behavior of the materials with that of 12-14 patient serum pools. In a total of 48 comparisons (12 materials x 4 pairs of analytical systems), seven instances of non-commutability were apparent, as shown by normalized residuals falling outside the +/-3 interval. The use of non-commutable materials generates two negative effects. In EQAS, the interlaboratory variation recorded is not representative of the variation expected in the assay of patient sera; in interlaboratory harmonization programs, recalibration with non-commutable materials increases, instead of decreasing, the interlaboratory variation. Both these effects were shown to occur in CEA measurement with the tested materials and systems. The materials planned to be used in our EQAS turned out to be commutable: this gave us the guarantee of measuring realistic interlaboratory variation values, although the check for commutability should be extended to all the analytical systems used by the participants in the scheme.
Letter to the Editor. To our knowledge, this is the first study reporting\ud
reference values for ALT, Amy, AST, GGT and LDH assuredly\ud
traceable to the IFCC standardization in uncomplicated\ud
pregnancy. The proposed reference intervals may\ud
be adopted by laboratories employing such standardized\ud
analytical methods
Background: To effectively assess and correct for intermethod variability, calibration and control materials (CCMs) must show the same intermethod behavior as patient sera, i.e., they must be commutable. We describe the commutability of selected CCMs for lipase assays, the impact of noncommutability of CCMs in normalizing patient results, and characteristics of reagents that affect assay specificity and commutability.
Methods: Lipase was measured in 98 patient sera and in 29 commercial CCMs, with 2 commercial methods using different substrates and with 4 experimental methods using 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6′-methylresorufin) ester as substrate and colipase as cofactor, but differing in the stabilizing proteins used and in the size of the substrate micelles.
Results: The noncommutability rate, i.e., the frequency of aberrant intermethod behavior of CCMs in comparison with patient sera, was 27% for liquid CCMs and 47% for lyophilized CCMs. The normalized residuals, measuring the degree of noncommutability, were −2.3 to 2.4 for CCMs with “normal” lipase activity, and −3.5 to 21.7 for CCMs with higher lipase activity. Recalculation of patient results with CCMs as calibrators decreased or increased the original bias according to whether the CCMs were commutable.
Conclusions: For the lipase methods in this study, the frequency of noncommutability of CCMs is affected by assay-specific characteristics, including size of substrate micelles and the presence or absence of added proteins.
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