Clinical Chemistry 44:3 632–638 (1998)
Commutability of control materials in glycohemoglobin determinations
Andrea Mosca,1* Renata Paleari,1 Alessandro Mad`e,1 Carlo Ferrero,2 Massimo Locatelli,2 and Ferruccio Ceriotti2
The intermethod variabilities of control materials and patient blood samples for the measurement of glycohe- moglobin were compared. Sets of 50 blood samples and 15 control materials were analyzed by HPLC and affin- ity and immunochemical methods. For each pair of methods, the distances of the materials from the regres- sion line of patient blood results (expressed as normal- ized residuals) were calculated. Only two of 15 controls had normalized residuals exceeding 3 standard devia- tions from the regression line. Total hemoglobin (Hb) content, Hb derivatives, and cellulose acetate electro- phoresis demonstrated that only a minority of controls could be considered similar to patients’ blood samples. We selected Menarini’s and our home-prepared controls to simulate calibration of the different techniques by these materials. Intermethod calibration succeeded mostly in harmonizing results obtained by HPLC meth- ods. On the contrary, calibration of the immunochemi- cal techniques (Boehringer and Roche) did not improve intermethod agreement to a clinically useful level.
In the last 10 years reference materials,
20 papers on the commutability of i.e., the ability that such materials
possess to show interassay properties comparable with those of human samples, have been published. The ma- jority deal with the measurement of enzyme activities [1, 2], serum proteins , and cholesterol . The lack of commutability of control materials has been considered a
Glycohemoglobin (glyHb) standardization is another subject that has been intensively debated over the last few years, especially after the evidence that the measurement of glyHb in blood is the best tool for the long-term monitoring of glycometabolic control in diabetics .3 To this purpose an IFCC working group on glyHb standard- ization is actually working to develop and validate a reference metrological system for Hb A1c determination, including primary and secondary reference materials, a reference method, and adjusted reference and target val- ues [7–9].
However, up to now no study has been performed on the commutability of control materials for glyHb deter- mination. Furthermore, the latest proposed secondary reference material for glyHb has been tested for stability, matrix effect, and homogeneity, not for commutability . Because control and reference materials are essential in assessing analytical methods and for data alignment, we decided to check the commutability of a set of com- mercially available control materials among the most widely used techniques for whole-blood glyHb determi- nation.
Our goal was to find a control material with good commutability that could be used as calibrator for the diverse assay methods actually used to measure glyHb in blood, and to try to ascertain which kind of harmoniza- tion of results obtained by different methods can be achieved by calibrating all the methods with the same material.
methods  and the fact that half been published after 1995 support of lack of commutability is an clinical chemistry.
of the papers that have the idea that awareness emerging problem in
Materials and Methods
Human blood samples (n
250) covering a wide range of
1 Department of Sciences and Biomedical Technologies, University of Milan, Italy. Istituto Scientifico H. S. Raffaele, Laboratorio di Analisi, Milan, Italy. *Address correspondence to this author at: Dip. Sc. Tecnol. Biomediche, 2
glyHb values and collected in the presence of EDTA were taken from the routine laboratory. The following commer- cially available control materials were also analyzed for
L.I.T.A., Via Fratelli Cervi 93, 20090 Segrate, Milano, Italy. Fax
e-mail email@example.com. Received July 21, 1997; revision accepted December 2, 1997.
3 Nonstandard abbreviations: glyHb, glycohemoglobin; MetHb, methemo- globin; NGSP, National Glycohemoglobin Standardization Program; and IGSP, International Glycohemoglobin Standardization Program.