Calibration of HbA1c and its measurement in the presence of variant haemoglobins: report on questionnaire to manufacturers

Abstract

Aims: To review 'Diabetes Control and Complications Trial (DCCT)-aligned' HbA1c reporting in UK, use of individual/network equations relating IFCC calibration to 'DCCT alignment', and whether HbA1c in the presence of variant haemoglobins is, according to manufacturers, suitable for current, clinical guidelines. Methods: Questionnaire sent to nine manufacturers and responses analysed. Results: All methods were certified as 'DCCT-aligned' by National Glycohemoglobin Standardization Program (NGSP); UK EQA schemes reported 95% of results 'DCCT-aligned' in December 2004. The master equation relating networks was used by six manufacturers and specific equations for individual methods by three. HbA1c results from laboratory/point of care testing analysers can be affected by variant haemoglobins including elevated HbF; only IE HPLC (and LPLC) detect their presence. If chromatographic separation is ideal in heterozygous patients, laboratories either choose not to report HbA1c and propose another strategy for monitoring glycaemia, or report HbA1c and issue a caution that it may not be appropriate for guidelines. HbA1c reported from immunochemistry or affinity chromatography in presence of variant haemoglobins, may not be reliable for use with clinical guidelines. Conclusions: For clinical care, HbA1c must reflect its relationship to glycaemia in clinical trials underpinning national guidelines. A flowchart to establish if HbA1c measurement is appropriate has been produced for use in a clinical setting.