COMMUTABILITY OF CONTROL MATERIALS IN GLYCOHEMOGLOBIN DETERMINATIONS

The intermethod variabilities of control materials and patient blood s amples for the measurement of glycohemoglobin were compared. Sets of 5 0 blood samples and 15 control materials were analyzed by HPLC and aff inity and immunochemical methods. For each pair of methods, the distan ces of the materials from the regression line of patient blood results (expressed as normalized residuals) were calculated. Only two of 15 c ontrols had normalized residuals exceeding 3 standard deviations from the regression line. Total hemoglobin (Hb) content, Hb derivatives, an d cellulose acetate electrophoresis 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 calibr ation of the different techniques by these materials. Intermethod cali bration succeeded mostly in harmonizing results obtained by HPLC metho ds. On the contrary, calibration of the immunochemical techniques (Boe hringer and Roche) did not improve intermethod agreement to a clinical ly useful level.