Practice Cases in primary care laboratory medicine

Glycated haemoglobin (HbA1c) monitoring

BMJ 2006; 333 doi: http://dx.doi.org/10.1136/bmj.38947.627847.AE (Published 14 September 2006) Cite this as: BMJ 2006;333:586
  1. Timothy M Reynolds, professor1,
  2. W Stuart A Smellie ([email protected]), consultant2,
  3. Patrick J Twomey, consultant3
  1. 1 Department of Clinical Chemistry, Queen's Hospital, Burton upon Trent DE13 0RB,
  2. 2Clinical Laboratory, General Hospital, Bishop Auckland DL14 6AD,
  3. 3Department of Chemical Pathology, Ipswich Hospital, Ipswich IP4 5PD
  1. Correspondence to: W S A Smellie
  • Accepted 9 August 2006

Glycation of haemoglobin to produce HbA1c occurs throughout the 120 day average lifespan of the red blood cell. Repeat testing in less than 120 days or situations that shorten this lifespan will produce HbA1c results that do not fully reflect current diabetic control

This article describes two common scenarios involving the use of glycated haemoglobin (HbA1c) that may be seen in primary care and considers their potential clinical implications in monitoring patients with diabetes.

HbA1c has become established as the monitoring test of choice to assess medium term diabetic control and as a key parameter on which to base changes in management of patients. Common situations exist, however, in which the HbA1c can be misleading. As the average lifespan of a red blood cell is approximately 120 days, in situations in which red cell lifespan is reduced HbA1c may not accurately reflect diabetic control. With increasing emphasis on achieving lower HbA1c values in patients with diabetes, clinicians need to be aware of these situations and understand the limitations of the test methods used.

Case 1

A 60 year old woman was seen for review of her diet controlled type 2 diabetes. She was also taking long term ferrous sulphate treatment because of caecal angiodysplasia. Otherwise, she seemed healthy with no specific problems except for being slightly overweight (body mass index 28). Her blood pressure was 144/94 mm Hg, and her haemoglobin was 12.3 g/dl (reference interval 11.5-16.5 g/dl). Random plasma glucose and HbA1c were measured and found to be 12.0 mmol/l and 7.4% respectively. Urine albumin excretion was also assessed—urinary albumin:creatinine ratio 1.5 mg/µmol (threshold < 3.5 mg/µmol to exclude micro-albuminuria). This was considered acceptable, and no change in treatment of her diabetes was considered necessary. Over the next year her haemoglobin remained stable; …

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