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Assessing intermediate-term glycemic control
Fructosamine is a general term, which applies to any glycated protein. It is formed by the nonenzymatic reaction of glucose with the a- and e-amino groups of proteins to form intermediate compounds called aldimines. These aldimines may dissociate or undergo an Amadori rearrangement to form stable ketoamines called fructosamines. This nonenzymatic glycation of specific proteins in vivo is proportional to the prevailing glucose concentration during the lifetime of the protein. Therefore, glycated protein measurement in the diabetic patient is felt to be a better monitor of long-term glycemic control than individual or sporadic glucose determinations. The best known of these proteins is glycated hemoglobin which is often measured as hemoglobin A1c, and reflects glycemic control over the past 6 to 8 weeks. In recognition of the need for a measurement that reflects intermediate-term glycemic control and was easily automated, a nonspecific test, termed fructosamine, was developed. Since albumin is the most abundant serum protein, it accounts for 80% of the glycated serum proteins, and thus, a high proportion of the fructosamine. Although a large portion of the color generated in the reaction is contributed by glycated albumin, the method will measure all proteins, each with a different half-life and different levels of glycation.
In general, fructosamine reflects glycemic control in diabetic patients over the previous 2 to 3 weeks. High values indicate poor control.
Since the assay is nonspecific, color may be generated by compounds other than glycated proteins. Interferences are seen from ascorbic acid (vitamin C) and elevated bilirubin values.
However, the second-generation assays have been shown to be highly specific for glycated proteins.
Fasting blood glucose and hemoglobin A1c are the usual and preferred means of monitoring glycemic control.
1. Tietz Textbook of Clinical Chemistry, Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders Company, 1999
2. Austin GE, Mullins RH, Morin LG: Non-enzymatic glycation of individual plasma proteins in normoglycemic and hyperglycemic patients. Clin Chem 1987;33:2220-2224
3. Schleicher ED, Mayer R, Wagner EM, Gerbitz KD: Is serum fructosamine assay specific for determination of glycated serum protein? Clin Chem 1988;34:320-323