Fructosamine

Fructosamine (frook-TOH-sah-meen) is a sugar-albumin complex that forms in chronic hyperglycemic conditions. A fructosamine test is a blood test that is used in animals to measure the average level of glucose control over the past few weeks. It's in proportion to the blood glucose concentration over the lifespan of the glycated protein being measured. The most common test for this in humans is the HbA1c, which is very much like the Ghb or glycosylated hemoglobin test shown on this page.

Both tests measure the level of glycosylated proteins in the blood. The higher the serum fructosamine concentration, the higher the blood glucose levels have been over the lifespan of the albumin protein, which is 1-2 weeks in dogs and is presumed to be the same in cats. The serum fructosamine concentration is meant to reflect the blood glucose concentration level over a 7-10 day period prior to testing.

Fructosamine testing is favored for humans over HbA1c in cases where the age of red blood cells may be affected, such as blood loss or certain types of anemia, where the test may not be reliable.

Serum fructosamine levels are significantly higher in untreated or poorly controlled diabetic pets compared with stressed or sick non-diabetic pets with hyperglycemia.

Glycosylated hemoglobin tests

Glycosylated hemoglobin (Ghb) or (Hb) tests use insulin binding of glucose to the hemoglobin. In this way, it measures the average blood glucose for several weeks prior to testing. Ghb or Hb is similar to the HbA1c tests for human diabetics, because it depends on the half-life of red blood cells.

Red blood cell life in dogs is 120 days; therefore a Ghb test will reflect average blood glucose concentration over an 8-12 week period. Halflife of red blood cells in cats is 66-78 days, so a Ghb test done on a cat reflects average blood glucose concentration over the 5-6 week period before testing. Glycosylated hemoglobin tests, like the human HbA1c above, can produce less than accurate results with concurrent health problems like anemia.

Stress and glucose testing

Stress hyperglycemia (the "white coat" syndrome some pets display with visits to the veterinarian) can approach diabetic levels, and can in some instances be high enough to cause glycosuria--glucose in the urine. (Personal experience of one canine caregiver indicates a reading can be 50+ points higher, depending on whether or not the pet liked the doctor or tech doing the blood draw.) Both fructosamine and glycosylated hemoglobin tests can help distinguish stress hyperglycemia from diabetic hyperglycemia when viewed in conjunction with other test results and clinical signs.

What fructosamine and Ghb tests cannot do

Neither of these tests alone can offer insight into possibly needed insulin dosage adjustments. A pet not receiving enough insulin will have a high fructosamine level. A pet receiving too much will also have high results because of the Somogyi rebound pattern which forces the body to release glucose. The resulting hyperglycemia of rebound reflects as elevated fructosamine concentrations.

What fructosamine and Ghb tests can do

The "plus" side of fructosamine and Ghb testing is learning how well overall glucose control has been over the past few weeks. The "minus" side is that they can't identify any possible problems. In short, they can tell you that you've gone wrong, but they can't tell you where. Worse, it's possible to get a good fructosamine result (average BG) while having very poor regulation (alternating highs and lows.) Fructosamine and Ghb tests are not intended to replace blood glucose curves, but to supplement them.

False fructosamine test results

High levels of Vitamin C (ascorbic acid) or circulating fat in the blood (lipemia) can interfere with fructosamine testing. The breakdown of red blood cells (hemolysis) or hyperthyroidism can also.

Further Reading

• Dr. Richard Nelson--On Feline Diabetes Management--pages 34 & 35 Page 35 has fructosamine test result interpretation table.
• A chart for converting fructosamine results to average blood glucose levels

• Canine fructosamine test reference chart and a comparison of fructosamine and glycosylated hemoglobin (Ghb) tests.

• Pets with Diabetes article on fructosamine tests