What is Fructosamine?
Also Known As:
Glycated Serum Protein, GSP
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.
Glucose molecules will permanently combine with proteins in the blood in a process called glycation. These 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 test, reflect average glucose levels over 2 to 3 weeks.
Keeping blood glucose levels as close as possible to normal helps individuals 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 people treated with insulin and by occasional monitoring of the effectiveness of treatment using the A1c test or the fructosamine test.
How is the test used?
Fructosamine testing may be used to help people with diabetes monitor and control their blood glucose levels in cases where the A1c test cannot be used and/or a shorter-term monitoring window is desired. 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.) However, what this translates to in regard to outcomes and prognosis is not as validated as with A1c.
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).
The American Diabetes Association (ADA) recognizes the usefulness of monitoring glucose control and suggests more frequent self-monitoring of blood glucose or changing the timing of continuous glucose monitoring in situations where A1c cannot be reliably measured. The ADA states that the prognostic significance of the results of a fructosamine test are not as clear as with A1c.
Instances where fructosamine may be considered over A1c include:
- Rapid changes in diabetes treatment – fructosamine allows the effectiveness of diet or medication adjustments to be evaluated after a few weeks rather than months.
- Diabetic pregnancy – in women with diabetes who become pregnant, good glycemic control is essential during pregnancy, and the needs of the mother frequently change during the pregnancy; fructosamine measurements may be ordered along with glucose levels to help monitor and accommodate shifting glucose, insulin, or other medication requirements.
- Shortened RBC life span – an A1c test will not be accurate when a person has a condition that affects the average lifespan of red blood cells (RBCs), such as hemolytic anemia or blood loss. When the lifespan of RBCs in circulation is shortened, the A1c result is falsely low and is an unreliable measurement of a person’s average glucose over time.
- Abnormal forms of hemoglobin – the presence of some hemoglobin variants, such as hemoglobin S in sickle cell anemia, may affect certain methods for measuring A1c. Furthermore, the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) recommends against the use of the A1c test in patients with the hemoglobin variants HbSS, HbSC, or HbCC as these patients may suffer from conditions that affect the A1c test, such as anemia, increased RBC turnover, and frequent blood transfusions.