Fructosamine is a compound that is formed when glucose combines with protein. This test measures the total amount of fructosamine (a glycated protein) in the blood. Since the fructosamine levels of people with well-controlled diabetes may overlap with those of people who are not diabetic, the fructosamine test is not useful as a screening test for diabetes.
High levels of vitamin C (ascorbic acid) and hyperthyroidism can interfere with test results.
Fructosamine testing may be used to help a person with diabetes monitor and control his or her blood glucose level. The level of fructosamine in the blood is a reflection of glucose levels over the previous 2-3 weeks. (See the “What is being tested?” section for more on this.)
Both fructosamine and A1c tests are used primarily as monitoring tools to help people with diabetes control their blood sugar. However, the A1c test is much more well-known and widely accepted because there are firm data that a chronically elevated A1c level predicts an increased risk for certain diabetic complications, such as problems with the eyes (diabetic retinopathy), possibly leading to blindness, kidney disease (diabetic nephropathy), and nerve damage (diabetic neuropathy).
Glucose molecules will permanently combine with proteins in the blood in a process called glycation. Affected proteins include albumin, the principal protein in the fluid portion of blood (serum), as well as other serum proteins and hemoglobin, the major protein found inside red blood cells (RBCs). The more glucose that is present in the blood, the greater the number of glycated proteins that are formed. These combined molecules persist for as long as the protein or RBC is present in the blood and provide a record of the average amount of glucose that has been present in the blood over that time period.
Since the lifespan of RBCs is about 120 days, glycated hemoglobin (hemoglobin A1c) represents a measurement of the average blood glucose level over the past 2 to 3 months. Serum proteins are present in the blood for a shorter time, about 14 to 21 days, so glycated proteins and the fructosamine tests reflect average glucose levels over a 2 to 3 week time period.
Keeping blood glucose levels as close as possible to normal helps those with diabetes to avoid many of the complications and progressive damage associated with elevated glucose levels. Good diabetic control is achieved and maintained by daily (or even more frequent) self-monitoring of glucose levels in insulin-treated diabetics and by occasional monitoring of the effectiveness of treatment using either a fructosamine or A1c test.
A high fructosamine means that a diabetic’s average glucose over the previous 2 to 3 weeks has been elevated. In general, the higher the fructosamine level, the higher the average blood glucose level. Monitoring the trend of values may be more important than a single high value. A trend from a normal to a high fructosamine level may indicate that a person’s glucose control is not adequate. This, however, does not pinpoint the cause. A review and adjustment to the person’s diet and/or medication may be required to help get the person’s glucose under control. Acute illness and significant stress can also temporarily raise blood glucose levels so these factors may also be taken into account when interpreting results.