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Unexpected high HbA1c results due to an unusual haemoglobin variant: an important clinical lesson
  1. Christopher N Floyd1,2,
  2. Sally Brady3,
  3. Daniel Monteiro4,
  4. Yashica Nathan5,
  5. Martin Crook3,6
  1. 1 Department of Clinical Pharmacology, Guy’s and St Thomas’ Hospitals NHS Trust, London, UK
  2. 2 King’s College London British Heart Foundation Centre, School of Cardiovascular Medicine and Sciences, King’s College London, London, UK
  3. 3 Department of Chemical Pathology, Guy’s and St Thomas’ NHS Foundation Trust, London, UK
  4. 4 Department of Special Haematology, Guy’s and St Thomas’ NHS Foundation Trust, London, UK
  5. 5 Department of Diabetes, University Hospital, Lewisham and Greenwich Trust, London, UK
  6. 6 Department of Clinical Biochemistry and Metabolic Medicine, Guy’s and St Thomas' and Lewisham and Greenwich Trust, London, UK
  1. Correspondence to Professor Martin Crook, Guy's Hospital, London SE1 9RT, UK; martin.crook{at}

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The measurement of glycated haemoglobin (Hb), reported as HbA1c, is recommended for the screening, diagnosis and monitoring of diabetes mellitus. HbA1c measurement usually provides an assessment of an individual’s glycaemic control over the previous 2–3 months and correlates with the development of diabetic complications. Standardisation of results attempts to ensure both intra- and inter-assay agreement so that an individual’s glycaemic control can be accurately monitored. Historically, standardisation was performed based on the Diabetes Control Complications Trial (HbA1c reported as a percentage), but more recently based on the International Federation of Clinical Chemistry (reported as mmol/mol).

However, despite robust approaches towards measurement standardisation, it is recognised that HbA1c results might not necessarily provide a true reflection of glycaemic control. HbA1c can be falsely lowered by conditions that shorten erythrocyte survival or decrease mean erythrocyte age (eg, acute blood loss or haemolytic anaemia) irrespective of the assay method.1 Furthermore, other factors such as the presence of a haemoglobinopathy, iron deficiency anaemia, hypertriglyceridaemia, hyperbilirubinaemia, uraemia or exogenous toxins may interfere with some assay methods but not others. In these instances, alternative methods for monitoring long-term glycaemic control (including total HbA1c, plasma glucose or fructosamine measurement) are recommended.2

The presence of interfering factors is not always obvious, especially in the case of haemoglobinopathies that are not evident either clinically or within standard haematological indices. Here we report a rare and novel case of HbJ-CapeTown (plus an alpha chain triplicated 3.7 Kb mutation) resulting in falsely elevated HbA1c results and highlight the importance of visual analysis of chromograms for the …

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  • Correction notice This article has been corrected since it first published. The provenance and peer review statement has been included.

  • Contributors YN and MC provided clinical care. SB and DM performed scientific assays. CNF and MC wrote the manuscript. All authors contributed to data analysis and approved the final submission. MC developed the concept for the article and is responsible for the overall content as guarantor.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.