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

BMJ 1994;309:983-986 (15 October)

Papers

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

E S Kilpatrick, A G Rumley, M H Dominiczak, M Small

Department of Pathological Biochemistry, Gartnavel General Hospital, Glasgow G12 OYN Diabetic Unit, Gartnavel General Hospital, Glasgow G12 OYN Correspondence to: Dr Kilpatrick, lipid and diabetes laboratory.

Abstract

Objective : To see whether two measures of glycated haemoglobinconcentration - the haemoglobin A1 (HbA1) value and the haemoglobinA1c (HbA1c) value - assess blood glucose control differentlyin diabetes.
Design : Diabetic patients had glycaemic control assessed onthe basis of HbA1 and HbA1c values measured by the same highperformance liquid chromatography instrument and on the basisof HbA1 measured by electrophoresis.
Setting : A diabetic outpatient clinic.
Subjects : 208 diabetic patients and 106 non-diabetic controls.
Main outcome measures : Glycated haemoglobin concentrationsclassified according to European guidelines as representinggood, borderline, or poor glycaemic control by using standarddeviations from a reference mean.
Results : Fewer patients were in good control (25;12%) andmore poorly controlled (157;75%) as assessed by the HbA1c valuecompared with both HbA1 assays (39 (19%) and 130 (63%) respectivelywhen using high performance liquid chromatography; 63 (30%)and 74 (36%) when using electrophoresis). The median patientvalue was 8.0 SD from the reference mean when using HbA1c, 5.9when using HbA1 measured by the same high performance liquidchromatography method, and 4.1 when using HbA1 measured by electrophoresis.
Conclusions : Large differences exist between HbA1 and HbA1cin the classification of glycaemic control in diabetic patients.The HbA1c value may suggest a patient is at a high risk of longterm diabetic complications when the HbA1 value may not. Betterstandardisation of glycated haemoglobin measurements is advisable.

Clinical implications

Clinical implications
Improved glucose control in diabetic patients reduces the risk of long term microvascular complications
HbA1 and HbA1c are glycated haemoglobins commonly measured to give an indication of glycaemic control over the preceding six to eight weeks
In this series HbA1 measurement classified fewer patients as poorly controlled and more as well controlled in comparison with HbA1c
Patients may thus appear to be at less risk of long term complications when HbA1 concentration rather than the more specific HbA1c concentration is measured
until standardisation to HbA1c measurement occurs doctors should be aware that care is required with the interpretation of glycated haemoglobin measurements

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