Fructosamine (glycated plasma proteins) is formed in the blood by the reaction of glucose with proteins. This reaction is identical to the reaction that occurs with hemoglobin inside the red blood cells to form HbA1c. The higher the glucose level, the greater the formation of fructosamine and HbA1c.
HbA1c represents the average glycemia for the 4 to 6 weeks prior to collection, and fructosamine for 2 to 3 weeks prior. Measuring fructosamine is therefore useful in any situation where blood sugar control needs to be assessed over a period shorter than one month and a half to two months (e.g., in pregnant women) and in rare cases involving an interference in the HbA1c measurement. The ratio of micromoles of fructosamine per gram of protein (µmol/g) is most useful in interpreting the results.
A high ratio indicates that the average glycemia in a diabetic individual was high in the 2 to 3 weeks prior to testing. The higher the ratio, the more poorly the blood sugar is being controlled. A normal ratio is found in non-diabetic individuals or in diabetic patients who are controlling their blood sugar well.