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Mosca et al.: Commutability of controls

method calibrators only for those pairs of methods for which commutability has been proven, we strongly sug- gest that, also in the case of glyHb measurement, the commutability of calibrators and controls should be tested before the materials are used in routine methods. We also propose that manufacturers clearly state that their own materials are intended for users of their products only, unless commutability studies haven proven their com- mutability with other methods. Moreover, we think that the criterion of not exceeding 3 normalized residuals from the regression line of patient samples could be acceptable for control materials. However, a more strin- gent criterion should be used for the acceptance of cali- brators, and our data seem to indicate that 1 normalized residuals is a more appropriate criterion in such cases. Finally, it is essential that the IGSP proceeds, since the intermethod calibration of some techniques (i.e., the im- munochemical methods) by common commercially avail- able calibrators may not succeed in harmonizing the glyHb results to a clinically useful degree.

We gratefully acknowledge A. Croce (H. Civile, Abbiate- grasso, Milano), C. Franzini (H. L. Sacco, Milano), E. Guagnellini (H. S. Paolo, Milano), and M. Plebani (H. Civile, Padova) for taking part in method comparisons. We thank A. Trapolino (Dip. Sc. Tecnologie Biomediche, Milano) and V. Agape (IRCCCS H. S. Raffaele, Milano) for their skillful help. Finally, we thank Abbott, Bayer, Bio- Rad, Boehringer, Menarini, and Roche for providing us their control materials as a generous gift. This work was partially supported by a grant from M.U.R.S.T. (aliquot 60%, A.M. recipient).

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