Glycated haemoglobin values: problems in assessing blood glucose control in diabetes mellitus

OBJECTIVE: To see whether two measures of glycated haemoglobin concentration--the haemoglobin A1 (HbA1) value and the haemoglobin A1c (HbA1c) value--assess blood glucose control differently in diabetes. DESIGN: Diabetic patients had glycaemic control assessed on the basis of HbA1 and HbA1c values measured by the same high performance liquid chromatography instrument and on the basis of HbA1 measured by electrophoresis. SETTING: A diabetic outpatient clinic. SUBJECTS: 208 diabetic patients and 106 non-diabetic controls. MAIN OUTCOME MEASURES: Glycated haemoglobin concentrations classified according to European guidelines as representing good, borderline, or poor glycaemic control by using standard deviations from a reference mean. RESULTS: Fewer patients were in good control (25;12%) and more poorly controlled (157;75%) as assessed by the HbA1c value compared with both HbA1 assays (39 (19%) and 130 (63%) respectively when using high performance liquid chromatography; 63 (30%) and 74 (36%) when using electrophoresis). The median patient value was 8.0 SD from the reference mean when using HbA1c, 5.9 when using HbA1 measured by the same high performance liquid chromatography method, and 4.1 when using HbA1 measured by electrophoresis. CONCLUSIONS: Large differences exist between HbA1 and HbA1c in the classification of glycaemic control in diabetic patients. The HbA1c value may suggest a patient is at a high risk of long term diabetic complications when the HbA1 value may not. Better standardisation of glycated haemoglobin measurements is advisable.