Fructosamine

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).

The American Diabetes Association (ADA) recognizes the usefulness of both tests and states that fructosamine may be considered as a substitute in situations where A1c cannot be reliably measured. Instances where fructosamine may be a better monitoring choice than 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 diabetic women who are pregnant, good glycemic control is essential during pregnancy, and the needs of the mother frequently change during gestation; 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. In these cases, fructosamine can be used to monitor glucose control.

Although not widely used, the fructosamine test may be ordered whenever a health practitioner wants to monitor a person's average glucose levels over the past 2 to 3 weeks. It is primarily ordered when a diabetic treatment plan is being started or adjusted in order to monitor the effect of the change in diet, exercise, or medication.

Fructosamine levels also may be ordered periodically when a diabetic woman is pregnant or when a person has an illness that may change their glucose and insulin requirements for a period of time. The fructosamine test may be used when monitoring is required and an A1c test cannot be reliably used, as in cases of a shortened RBC life span or in some cases where the person being tested has an abnormal hemoglobin.

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.

A normal fructosamine level may indicate that a diabetic has good diabetic control and that the current treatment plan is effective for the individual. Likewise, a trend from high to normal fructosamine levels may indicate that changes to a person's treatment regimen have been effective.

Fructosamine results must be evaluated in the context of a person's overall clinical findings. Falsely low fructosamine results may be seen with decreased blood total protein and/or albumin levels, with conditions associated with increased protein loss in the urine or gastrointestinal tract, or with changes in the type of protein produced by the body. In this case, a discrepancy between the results obtained from daily glucose monitoring and fructosamine testing may be noticed. Also, someone whose glucose levels swing erratically from high to low may have normal or near normal fructosamine and A1c levels but still have a condition that requires frequent monitoring. However, most people with such unstable diabetic control do have elevated fructosamine and A1c concentrations. 

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.