Determination of haemoglobin A1c by iso-electric focusing. Effect of incubation of erythrocytes and comparison of results obtained by ion-exchange chromatography.

Blood samples from 24 non-diabetics and 26 diabetics were analysed using both thin layer iso-electric focusing and ion-exchange chromatography. Using isoelectric focusing it was found that about 10% of haemoglobin A1c (0.7-1.2% of total haemoglobin) could be removed by a preceding incubation of the erythrocytes in saline at 37 degrees C for 6 h. When glucose was added to the incubation medium in a final concentration of 25 mmol/l no decline was seen in the concentration of haemoglobin A1c. Using similar treatment of erythrocytes identical results were obtained by the two methods. A reference interval for normal subjects (age range 6 months to 65 years) was established for the iso-electric focusing method using non-incubated samples.