Pets with Diabetes: Fructosamine and glycosylated Hemoglobin

Fructosamine and Glycosylatated Hemoglobin (Hb) blood tests are blood tests that are used to measure the average level of glucose control over the past few weeks.

Hemoglobin (Hb) is the protein in red blood cells that carries oxygen. Serum albumins are a group of several proteins that occur naturally in the blood. All of these proteins are constantly being manufactured by the body. The life-span of a red blood cell and its hemoglobin is about 120 days (17 weeks). The life-span of serum albumins is between about 1 to 3 weeks, depending on the specific protein. In cats, the life-span of the proteins being measured in a fructosamine test is about 1-2 weeks.

Hb and serum albumins can bind (connect to) glucose. When this binding occurs, the protein is said to be glycosylated. The amount of binding depends on two factors: how long the proteins have been in the body, and the amount of glucose in the blood during the life-span of the protein. The binding is irreversible, so after the protein binds glucose, they stay bound.

Glycosylated Hb and fructosamine tests measure how many proteins have been glycosylated. In other words, how many proteins have glucose connected to them. Fructosamine is a sugar-albumin complex.

These tests are used to measure the average level of glucose control. The higher the level of glycosylated Hb or fructosamine above normal, the poorer the average glycemic (glucose) control. The glycosylated Hb reflects the average glucose control over the past 120 days (approximately). Since the serum albumins are shorter-lived, the fructosamine test reflects average glucose control for the past 1-3 weeks.

Glycosylated Hb and fructosamine levels have been studied in diabetic cats and dogs, and they have been shown to correlate with the severity of hyperglycemia. Therefore, these tests can be used to monitor the average level of glucose control. Most pets get fructosamine tests, and not glycosylated Hb tests. This might be due to the cost, or the availability of labs doing the different tests.

Elevated glycosylated Hb or fructosamine values reflect poor glucose control and indicate the need for a change in insulin therapy. Since these tests reflect the average control, they do not identify the specific problem. Serial blood glucose measurements (a blood glucose curve) are needed to determine how to adjust the insulin.

Also, a "normal" glycosylated Hb or fructosamine test result can be obtained from an animal where the bg fluctuates between high and low values. Remember: these tests indicate the average level of bg control.

Note: If you have a glycosylated Hb or fructosamine test done on your pet, make sure you obtain the reference values from the lab that ran the test. Different labs will have very different "normal" values. You can not compare numbers between labs. Your vet must obtain the "low", "normal", and "high" numbers from the lab that performed the blood test, and evaluate your pet's results based on those reference values.

A note on cost: when we had a fructosamine test done on Barney, it was about $40. This is typical of what other owners have reported.

A few in-depth, technical details: In humans, glycosylated Hb is the most commonly measured glycosylated protein. There is one major fraction of hemoglobin (HbA1c) which binds glucose, and there are two minor fractions (HbA1a and HbA1b) which do not bind glucose. Because it is tedious to separate these different fractions, most techniques used in commercial labs measure total glycosylated Hb concentration (HbA1), which has been shown to be a clinically valid measure of degree of diabetic control. Depending on the methodology, however, acute hyperglycemia may cause an increase in the concentration of HbA1.

References
Ettinger's Textbook of Veterinary Internal Medicine
Diabetes & Hormone Center of the Pacific
SouthPaws Veterinary Referral Center

	Fructosamine & glycosylated Hemoglobin