March 14, 2007

Commentary By: Christopher Johnson, MSIV and Glenn Matfin, MD Clinical Associate Professor of Medicine, Divsion of Endocrinology When was the last time you had a diabetic patient in clinic whose hemoglobin A1C was elevated, prompting you to modify their diabetic regimen? You may have scheduled a repeat hemoglobin A1C in 3 months, since you know A1C measures glycemic control over a 3 month period. A serum fructosamine may help give you a snapshot of more recent control. What is fructosamine? Fructosamine is a compound that is formed by the non-enzymatic reaction between fructose and ammonia or an amine, with a molecule of water being released. Fructosamines are also formed when the carbonyl group of glucose reacts with an amino group of a protein. When fructosamines are formed from blood proteins such as albumin, they are known as Glycated Serum Protein or Glycated Albumin. Since albumin has a much shorter half-life than hemoglobin, serum fructosamine generally reflects the state ofglycemic control for only the preceding 2 weeks. Is serum fructosamine level a useful test? Fructosamine testing has been available since the 1980s as a monitoring tool to help diabetics control their blood sugar. The test for serum fructosamine is simpler and less costly than that for hemoglobin A1C, but at present is less frequently used. The level of fructosamine correlates well with fasting glucose and with hemoglobin A1C levels [1]. This correlation is strengthened when the fructosamine level takes into account the serum albumin concentration [2]. For several years, there was a home fructosamine meter that allowed patients to monitor their own fructosamine weekly, but it was taken off the market by the manufacturer because of inaccurate readings. The American Diabetes Association (ADA) recognizes the utility of both tests, and says that fructosamine may be a better choice when A1C cannot be reliably measured. These situations include: 1) The evaluation of changes in diabetictreatment, since the effects of adjustment can be evaluated after a couple of weeks rather than months. 2) In pregnancy, since the glucose and insulin needs of the mother and fetus change rapidly during gestation. 3) Any condition that affects the average age of red blood cells, such as hemolytic anemia, sickle cell anemia, or blood loss. Fructosamine is not affected by such conditions, and may be a better choice for monitoring glucose control. When is fructosamine not a useful test? Measured fructosamine may be falsely low in the setting of decreased protein levels, such as nephrotic syndrome or hepatic disease. Further, because of lack of standardization and concern with reproducibility, fructosamine is not recommended for routine use, or as a replacement or supplement for A1C when the A1C appears to be providing an accurate representation of glycemic control. How is a serum fructosamine level interpreted? As with many lab values, the reference range is different from lab to lab, so