title: A spuriously 'normal' haemoglobin A1c result.
abstract: We report a case of spuriously 'normal' haemoglobin A1c (HbA1c) result due to misidentification of HbG Taipei as HbAo by the Variant II built-in retention time algorithm. The defect was circumvented effectively by the implementation of a chromatographic system specific internal quality control mechanism for peak identity verification. HbA1c and estimated average glucose results were corrected from 4.7% to 8.2%, and 4.9 to 10.5 mmol/L, respectively. The results were consistent with the patient's concurrent and previous fasting blood glucose concentrations and existence of diabetes mellitus dermopathy, indicating poor glycaemic control. A review of currently available analytical systems showed that other than mass spectrometry, HbA1c measurements by these systems were generally affected by the presence of haemoglobin variants. The same haemoglobin variant may affect different analytical systems differently, resulting in the deviation of HbA1c results from the true value to different extents. Including the analytical principle of HbA1c measurement in the laboratory report can avoid inappropriate comparison of results obtained by different analytical systems. Moreover, since individual haemoglobinopathy may affect the degree of glucose binding to haemoglobin in a different way, this uncertainty limits the general application of same decision cut-off of established guidelines for glycaemic control monitoring. Adoption of an individualized monitoring system based on the critical difference or reference change value of HbA1c can be considered.
authors.affiliation: Clinical Pathology Laboratory, Department of Pathology, Hong Kong Sanatorium and Hospital, University of Hong Kong, Hong Kong SAR. mhlo@hksh.com
authors.forename: Vanessa Man Har
authors.initials: VM
authors.lastname: Lo
authors.forename: Edmond Shiu Kwan
authors.initials: ES
authors.lastname: Ma
authors.forename: Elaine Mo Chee
authors.initials: EM
authors.lastname: Chau
authors.forename: Jason Chi Chiu
authors.initials: JC
authors.lastname: So
mesh_terms: D000368:Aged; D000818:Animals; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D008297:Male; D051381:Rats; D012016:Reference Values; D012680:Sensitivity and Specificity
chemical_list: D006442:Glycated Hemoglobin