Glycated serum protein determination: comparison between thiobarbituric acid and fructosamine assays

Glycated Serum Albumin and AGE Receptors

In vivo modification of proteins by molecules with reactive carbonyl groups leads to intermediate and advanced glycation end products (AGE). Glucose is a significant glycation reagent due to its high physiological concentration and poorly controlled diabetics show increased albumin glycation. Increased levels of glycated and AGE-modified albumin have been linked to diabetic complications, neurodegeneration, and vascular disease. This review discusses glycated albumin formation, structural consequences of albumin glycation on drug binding, removal of circulating AGE by several scavenger receptors, as well as AGE-induced proinflammatory signaling through activation of the receptor for AGE. Analytical methods for quantitative detection of protein glycation and AGE formation are compared. Finally, the use of glycated albumin as a novel clinical marker to monitor glycemic control is discussed and compared to glycated hemoglobin (HbA1c) as long-term indicator of glycemic status.

Glycated serum proteins and glucose tolerance

Glycated serum proteins (GSP), stable glycated hemoglobin (HbA1c) together with some metabolic parameters were evaluated in 120 subjects, 30 with normal glucose tolerance (NGT), 30 with impaired glucose tolerance (IGT), 30 with non-insulin-dependent diabetes mellitus (NIDD), and 30 with insulin-dependent diabetes mellitus (IDD). GSP levels were significantly higher in IGT, NIDD and IDD than in NGT. HbA1c levels were not significantly higher in IGT in comparison with NGT, but were significantly higher in NIDD and in IDD than in NGT and IGT. GSP correlated better than HbA1c with all metabolic parameters considered. Taking into account the distribution of the values, GSP showed a smaller overlap than HbA1c in all four groups studied. Moreover, only 9 subjects (30%) with IGT showed GSP levels above the normal range. Therefore, GSP assay is able to distinguish between normal and diabetic subjects but is unable by itself to discriminate subjects with normal from those with reduced glucose tolerance.