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Fructosamine

Clinical significance

A fructosamine test has been available through laboratories since the early 1980s. The main adventage of the test is that it can detect overall changes in blood glucose control within a few weeks, rather than months. Fructosamine levels indicate the level of blood glucose control over the past two or three weeks. When changes are being made in a diabetes treatment plan, this test can indicate in a more timely fashion than an HbA1c test how well the changes are working and whether other changes should be considered.(51)
Fructosamine levels are directly proportional to serum protein levels (albumin, immunoglobulins). Since the fructosamine level is not given as a percentage of actual serum total protein, a low level may indicate good control or it may indicate low total protein. Not all proteins are glycated at the same rate. Although normal serum protein is largely albumin, in patients with abnormally elevated levels of proteins other than albumin, glycation rates may shift affecting fructosamine levels as well.

Since many diabetics can maintain average glucose levels in the normal range, there is no clear distinction between a «normal» and «diabetic» specimen. The higher the fructosamine value, the poorer the degree of glycamic control. Because of this overlap between normal and diabetic ranges, the assay by itself cannot serve as an indicator of diabetes. Relative changes in fructosamine values for a specific individual may have more diagnostic significance than the absolute value.(52)

Variations in levels of serum proteins (albumin, IgA, and other immunoglobulins) may affect fructosamine results. High levels of ascorbic acid also interfere with the fructosamine assay. Patients should abstain from ascorbic acid supplements for a minimum of 24 hours prior to sample collection.

One mechanism of potential pathogenic importance of diabetes complications is nonenzymatic glycosylation of proteins. The effect of such glycosylation on multiple proteins in the body causes their disturbed functions.
Examples include:
• plasma albumin,
• lens protein,
• fibrin,
• collagen,
• lipoproteins,
• and the glycoprotein system of hepatic endothelial cells.

It is very important the effect of glycosylation on lipoproteins. Glycosylated low-density lipoprotein (LDL) is not recognized by the normal LDL receptor, and its plasma half-life is increased.
Conversely, glycosylated high-density lipoprotein (HDL) turns over more rapidly than native HDL.
It has also been reported that glycosylated collagen traps LDL at rates two or three times greater than normal collagen. Conceivably the accelerated atherosclerosis of diabetes might be related to the combined effect of a glycosylated LDL that did not bind normally to LDL receptors but would be trapped to a greater than normal extent in macrophages and glycosylated collagen of blood vessels and other tissues. Dysfunctional HDL could contribute by diminishing cholesterol transport out of affected sites.

Glycosylated collagen is less soluble and more resistant to degradation by collagenase than native collagen. It is not clear that this is related either to the basement membrane thickening or the tight, waxy skin syndrome with limited joint mobility (scleroderma-like) seen in some patients with insulin-dependent diabetes. Nonenzymatic glycosylation of proteins plays a role in some degenerative complications.
The fructosamine test can be potentially helpful for people making changes in their diabetes treatment plan. It can also be helpful to people with diabetes who do not closely monitor their blood sugar levels with multiple daily home tests. But, a once-a-week fructosamine test should not take place of regular visits to a doctor and regular hemoglobin A1c tests. Also, a normal fructosamine test doesn't mean that the patient blood sugars have been normal for the past 2-3 weeks. Someone with wide swings in blood sugars levels-lots of highs and lows-would also have a normal fructosamine test, but would really have serious problems with their overall treatment plan that require adjustment. This would be uncovered by frequent daily home blood sugar monitoring. Also, people should not be tempted to shoot for too low of a fructosamine level, as this might result in dangerous low blood sugars.

Fructosamine test offers information that augments that provided by home blood sugar monitoring and hemoglobin A1c provide. For people who are changing a treatment program it may be particularly useful. For those who currently are not doing frequent blood sugars tests at home, it may provide a first step towards getting oriented more towards home testing and taking action in overall diabetes management. (51)