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Glycated protein levels

Fructosamine and glycosylated hemoglobin

Fructosamine and glycosylated hemoglobin (GHb) are 2 glycated proteins commonly used for monitoring diabetic human patients. These 2 proteins are markers of mean glucose concentration and their amount is proportional to the blood glucose concentration. The concentration of these proteins is not affected by stress, therefore they are often used by veterinary practices to diagnose and monitor diabetic cats.

Although fructosamine and GHb are good tools for determining regulation, they will not identify an underlying problem, nor will they replace glucose curves done for therapy adjustments. Rather, they give an idea of glycemic control over a long period: fructosamine reflects the glycemic control for the previous 2 to 4 weeks and GHb for the prior 2 to 4 months.

Fructosamine is preferred over GHb to assess glycemic control. It is more commonly evaluated than GHb, because simpler, less time-consuming analytical assays are available. Also, successful monitoring and regulation can be achieved with weekly or monthly measurements of serum fructosamine.


The majority of diabetic animals will not always have optimal control of blood glucose; thus, fructosamine concentrations are unlikely to lie entirely within the reference range for normal cats. Single fructosamine measurements should be interpreted in the light of clinical signs, body weight, and blood glucose concentration. In general, the closer the fructosamine concentration is to the reference range for healthy cats, the better the glycemic control.

Fructosamine reference ranges6

Cats Fructosamine values (µmol/L)
Normal non-diabetic cats 190–365
Newly diagnosed diabetic cats 350–730
Regulated diabetic cats:
Excellent control 350–400
Good control 400–450
Fair control 450–500
Poor control >500
Prolonged hypoglycemia <300

Advantages of measuring fructosamine

  • Distinguishes hyperglycemic, non–diabetic cats from diabetic cats with chronic hyperglycemia.
  • Not influenced by stress hyperglycemia in cats.
  • Useful in confirming diagnosis in cats.
  • Helps evaluate long-term control and owner compliance with insulin treatment.

Limitations of fructosamine measurements

  • Unable to detect short-term or transient abnormalities in the blood glucose concentration, eg, transient daily episodes of hypoglycemia. This would require serial measurement of blood glucose concentrations.
  • Hyperthyroid cats with diabetes mellitus may have decreased fructosamine concentrations despite having normal serum protein concentrations. This results from an increase in the protein turnover rate (decreased protein half-life) caused by increased thyroid hormone concentrations.
  • Globulin and fructosamine concentrations are correlated in cats. Hypoglobulinemia will result in decreased fructosamine concentration—consult the laboratory performing the analysis as to whether a correction is required and whether this has been done.

Glycosylated hemoglobin (GHb)

GHb is produced by the non-enzymatic, irreversible binding of glucose to hemoglobin in erythrocytes. The glycation of hemoglobin is a gradual process and is not affected by acute or transient hyperglycemia.

Use GHb concentration as a screening test for diabetes mellitus, as well as to monitor glycemic control in treated diabetic animals.

Advantages of GHb measurements

  • Unaffected by stress-related or postprandial hyperglycemia.
  • Useful in long-term monitoring of diabetic animals over the previous 2 to 3 months.

Limitations of GHb measurements

  • Test not widely available for cats.
  • Not the most effective test due to the relatively long erythrocyte lifespan (~68 days in cats).
  • Less effective for short-term monitoring than fructosamine, because hyperglycemia must be present for at least 3 weeks before increased values are detectable.
  • Affected by hemoglobin concentrations—may be increased or decreased due to polycythemia or anemia, respectively.

Test results and interpretation vary greatly depending on the literature consulted and the laboratory where the test is performed. So, it’s best to ask each laboratory for guidelines to help with interpretation of results.

To submit blood samples to a laboratory, use red-top serum tubes for fructosamine and EDTA, lavender-top whole-blood tubes for GHb.

Suggested additional reading

  • Feldman EC, Nelson RW. Canine and Feline Endocrinology and Reproduction. 3rd ed. St. Louis, MO: Saunders; 2004.
  • Rand JS, Marshall RD. Diabetes mellitus in cats. Vet Clin North Am Small Anim Pract. 2005;35(1):211–224.