Monday, November 19, 2012

Fructosamine and it's implications


Fructosamine is a ketoamine product of protein glycation formed when glucose bound to variety of proteins by aldimine linkage undergoes an Amadori rearrangement. The major component of fructosamine in plasma is Glycated albumin. Fructosamine is easily measured (using nitroblue tetrazolium assay); its concentration reflects control over the preceding 15-20 days. When the patient has abnormal hemoglobins, or during pregnancy alternative tests should be used. Glycated albumin and Glycated fibrinogen are proposed for such conditions. Albumin has half life of approximately 20 days, so fraction that is Glycated reflects glycaemic control for the preceding 1-2 weeks.
(Source: Tietz Clinical Chemistry, 4th Edition)

Fructosamine is the generic name for plasma protein ketoamine. There is interaction of glucose with the ε-amino group on lysine residue of albumin. Because all Glycated serum proteins are fuctosamines and albumin is the most abundant serum protein, measurement of fructosamine is thought to be largely a measure of Glycated albumin. As fructosamine determination monitors short term glycemic changes different from GHb, it may have a role in conjunction with GHb rather than instead of it. In addition fructosamine may be useful in patients with hemoglobin variants such as HbS or HbC that are associated with decreased erythrocyte lifespan where GHb is of little value. Fructosamine values are highly affected and not recommended in conditions that affect protein turnover like liver cirrhosis, nephrotic syndrome or dysproteinemias, inflammatory conditions. It is generally accepted that the test should not be performed when serum albumin is less than 30g/L.
Methods for measuring Glycated proteins include affinity chromatography using immobilized phenylboronic acid, HPLC of Glycated lysine residue after hydrolysis of Glycated proteins, photometric procedure in which mild acid hydrolysis releases 5-hydroxymethylfurfural- proteins are precipitated with TCA and the supernatant is reacted with 2-thiobarbituric acid; and other procedures using phenylhydrazine and furosine.  Another method is under alkaline conditions which results in fructosamine undergoing an Amadori rearrangement and the resultant compounds having reducing activity that can be differentiated from other reducing substances. In the presence of carbonate buffer, fructosamine rearranges to the eneaminol form, which reduces NBT to a formazan. The absorbance at 530 nm is measured at two time points and the absorbance change is proportional to the fructosamine concentration. 

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