Annals of Clinical Biochemistry > Volume 45, Number 4 > Pp. 421-425

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Original Articles

Clinical impact of variability in HbA_1c as assessed by simultaneously measuring fructosamine and use of error grid analysis

David R Macdonald¹, Alison M Hanson², Martin R Holland³ and Baldev M Singh²

¹ Albrighton Medical Practice, Shaw Lane, Albrighton, Wolverhampton, West Midlands WV7 3DT, UK; ² Wolverhampton Diabetes Centre; ³ Clinical Chemistry, New Cross Hospital, Wolverhampton, West Midlands WV10 OQP, UK

Corresponding author: Dr David R Macdonald. Email: davidmacdonald{at}doctors.org.uk

Background: Haemoglobin A_1c (HbA_1c) is the only measure of glycaemic control used for many patients with diabetes, but it has limitations and might sometimes be misleading. HbA_1c concentrations are influenced by conditions that alter red-cell life and there is evidence that biochemical variation in intracellular glycation rates also influence HbA_1c concentrations. This paper is the first to propose a method of using simultaneously measured HbA_1c and fructosamine, and error grid analysis, in the clinical setting, to gain a better understanding of glycaemic control.

Methods: Cross-sectional analytical study using HbA_1c and fructosamine measures on the same blood sample from 1744 patients having blood taken for hospital diabetes clinic appointments. No other selection or exclusion criteria were applied.

Results: The fructosamine results were converted to a HbA_1c equivalent which was then compared with the HbA_1c. In an Altman-Bland plot, the paired result differences ranged between –6.9% and +5.5% HbA_1c with 1139 (65%), 438 (25%), 130 (8%) and 37 (2%) being 1%, 1–2%, 2–3% or >3% of HbA_1c difference, respectively. In clinical error grid analysis, 864 (50%) results had tight concordance for clinical interpretation, 761 (43%) had one block disunity of probably little clinical significance, but 105 (6%) were two blocks and 14 (1%) were three blocks discordant.

Conclusion: HbA_1c may not accurately reflect glucose control. Our method, utilizing co-assessment with serum fructosamine, evaluates the possible clinical impact of this. We suggest the analysis used in this paper should be used routinely in diabetes practice.

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