Fructosamine

Fructosamine and glycosylated haemoglobin (GHb) are two glycated proteins commonly used for monitoring human diabetics.

These two proteins are markers of mean blood glucose concentration, with their concentration being proportional to the blood glucose concentration. The concentration of these proteins is not affected by stress; they are ideal for monitoring diabetic animals. In practice they are often used for the diagnosis and monitoring of diabetic cats.

Fructosamine

The bonding of glucose to proteins produces fructosamines. In dogs glucose has a greater affinity for albumin and in cats globulins. A single fructosamine measurement indicates the average glucose concentration over the previous 1-2 weeks, based on the half-life of the plasma proteins.

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 dogs and cats. Single fructosamine measurements should be interpreted in the light of clinical signs of diabetes, body weight and blood glucose concentration. In general, the closer the fructosamine concentration is to the reference range for healthy dogs and cats, the better the glycaemic control.

Fructosamine reference ranges

(Reference: Feldman EC, Nelson RW (2004) Canine diabetes mellitus. In Canine and Feline Endocrinology and Reproduction. 3rd edition. Saunders, St Louis, USA p. 510)

(Reference: Feldman EC, Nelson RW (2004) Feline diabetes mellitus. In Canine and Feline Endocrinology and Reproduction. 3rd edition. Saunders, St Louis, USA p. 563)

Advantages of measuring fructosamine

• Distinguishes hyperglycaemic, non-diabetic animals from diabetics with chronic hyperglycaemia
• Does not appear to be influenced by transient hyperglycaemia (stress hyperglycaemia in cats)
• Useful in confirming diagnosis in cats
• Useful in evaluating longer-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, e.g. transient daily episodes of hypoglycaemia. 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 due to an increase in the protein turnover rate (decreased protein half-life) due to increased thyroid hormone concentrations.
• Fructosamine concentrations increase in hyperproteinaemia (e.g. hyperalbuminaemia due to dehydration in dogs).
• Albumin and fructosamine concentrations are highly correlated in dogs. Dogs with hypoalbuminaemia also have a decreased fructosamine concentration (false negative) – the laboratory performing the analysis should be consulted as to whether a correction is required and whether or not this has been done.
• Globulin and fructosamine concentrations are correlated in cats. Hypoglobulinemia will result in a decreased fructosamine concentration – the laboratory performing the analysis should be consulted as to whether a correction is required and whether this has been done or not.