285 - Detection of abnormal haemoglobins using a dedicated HbA1c test
Autor(s): M. Mercadanti, A. Caleffi, E. Bonilauri, C. Monica
Issue: RIMeL - IJLaM, Vol. 4, N. 4, 2008 (MAF Servizi srl ed.)
Page(s): 285-293
Background. Diabetes mellitus is a pathology associated with severe complications: the fundamental objective of preventing them is constituted by the achievement of good glycaemic control. The level of glycosylated haemoglobin (Hb A1c) is an essential parameter for monitoring glycaemic control as it has been found to be correlated to the complications of diabetes. Haemoglobin-related diseases have a high incidence in Mediterranean countries. The purpose of the study is to verify the incidence of haemoglobin variants observed during A1c testing in samples from external outpatient clinics and inpatient wards, and to assess the impact of structural variants on A1c levels, using the HPLC (high-pressure liquid chromatography) technique. Methods. Between 2004 and 2007, we selected all samples submitted for A1c testing by HPLC (A1c, Variant II HbA2/HbA1c Dual Program, Bio-Rad, Milan, Italy), whose chromatograms showed abnormal peaks or patterns suggesting the presence of haemoglobin disorders. The same samples were tested using the β- Thal method (Variant II HbA2/HbA1c Dual Program, Bio-Rad), which also gives the A1c value. A complete blood count was obtained from every patients. Results. 219 cases with structural variants and/or HPFH/βδ thalassaemia were observed, distributed as follows: 19 in 2004, 37 in 2005, 51 in 2006 and 112 in 2007, for a total of 115 patients, 56 male and 59 female, with an average age of 55 for males and 46 for females. Having excluded multiple tested and known cases, the number of patients with incorrectly diagnosed variants was 16 in 2004, 21 in 2005, 29 in 2006, 45 in 2007; 45 subjects were in follow-up. The A1c values, which were compared in 139 cases, were similar with the two methods: average value 7.09 % (+/- 2.03 SD) for the A1c method; 7.02 % (+/- 1.95 SD) for the β-Thal Method. The average values of A1c, broken down by type of variant, were perfectly correlated in the two methods for HbS (54 cases), and HbC (12 cases), δchain variants (31 cases) and HPFH/ βδ(11 cases), and were only slightly different in 17 cases of non-structurally identified variants. In the presence of Hb Toulon and G-Copenaghen the value obtained using the β-Thal method was the most accurate. In 2006, of a total of 16,145 test requests, corresponding to 11,486 patients, cases with variants constituted 0.44% of patients. Conclusions. The HPLC system detects the presence of structural variants, even when present in minimal percentages, as δchain variants (0.5-1.4%). The presence of S, C and δvariants and the consistent elevation of HbF do not interfere with the A1c value in HPLC. Only the less common variants required use of the β-Thal method, that, by performing a clear separation of the haemoglobin fractions, provides an accurate A1c value, even in the presence of this kind of haemoglobin variants.