title: Comparison of advanced glycation endproducts on haemoglobin (Hb-AGE) and haemoglobin A1c for the assessment of diabetic control.
abstract: Glycation process in vivo results in two different products: early and advanced glycation endproducts (AGEs). The mechanism of early product formation has been well described, with HbA1c as the best-studied example. The finding that advanced glycation endproducts are also formed on haemoglobin suggests that HbA1c is a precursor for Hb-AGE formation. HbA1c has been well established as an important indicator for glycaemia monitoring, but the diagnostic role of Hb-AGE has not yet been clarified. A question is whether HbA1c and Hb-AGE are competitive or complementary parameters. In our study, Hb-AGE was quantified by the competitive ELISA technique using polyclonal anti-AGE-RNase antibodies to detect AGE immunoreactivities of proteins precipitated in red cell hemolysate. Results are expressed as AGE units/mg Hb. Hb-AGE was analysed in three groups of patients divided according to HbA1c values as follows: group I (n = 25) HbA1c < 7%, Hb-AGE = 6.93 (5.7-7.3) U/mg; group II (n = 25) HbA1c = 7-10%, Hb-AGE = 8.62 (7.7-10.2) U/mg; and group III (n = 25) HbA1c > 10%, Hb-AGE = 12.47 (10.8-13.9) U/mg (median (interquartile range)). A close relation between the amounts of red cell HbA1c and Hb-AGE was observed in all diabetic subjects (n = 75) r = 0.77, P < 0.001. Patients with HbA1c level > 8% were considered to be in poor glycaemic control and those with HbA1c < 8% in good control. In the well-controlled subgroup (n = 33), HbA1c and Hb-AGE were less tightly correlated (r = 0.37, P <0.001). However, in those patients with a higher level of HbA1c = 12.55 (8.9-13.3)% (n = 42), the related Hb-AGE was 11.5 (10.3-12.8) U/mg Hb, yielding a more significant correlation (r = 0.51, P < 0.001). The content of Hb-AGE did not correlate with age (r = 0.09), diabetes duration (r = 0.05) or severity of retinopathy and/or nephropathy. The observed difference may reflect a different kinetic rate of HbA1c production and subsequently the rate of Hb-AGE formation. The discrepancy in the correlation between HbA1c and Hb-AGE suggests that they are complementary rather than opposed parameters. The amount of haemoglobin-linked AGEs does not correlate with the presence or absence of retinopathy and/or nephropathy. It seems that Hb-AGE represents only the metabolic status, equally in the subjects with and without diabetic microangiopathy.
authors.affiliation: University Clinic for Diabetes, Endocrinology and Metabolic Diseases, Zagreb, Croatia. zturk@indija.idb.hr
authors.forename: Z
authors.initials: Z
authors.lastname: Turk
authors.forename: R
authors.initials: R
authors.lastname: Mesić
authors.forename: B
authors.initials: B
authors.lastname: Benko
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism*; D017127:Glycation End Products, Advanced / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin; D017127:Glycation End Products, Advanced