Fructosamine Service Update

As of 24th June 2019 IDEXX Reference Laboratories is providing updated reference intervals for canine and feline fructosamine results. Comparing an individual patient’s serum fructosamine result to a validated reference interval is an important component in determining the health of a patient. Very few laboratories perform their own reference interval studies because of the time commitment and resources required. IDEXX is committed to providing our clients with the most accurate and reliable results possible. Therefore, we have taken the time and committed the resources to generate our own method specific reference intervals based on current scientific recommendations.¹

Fructosamine is formed by the irreversible binding of glucose to serum proteins. It reflects the average blood glucose (BG) level over the last 1-3 weeks and therefore the higher the mean BG is over time, the higher the fructosamine will be. Fructosamine results should only be compared with measurements run on the same analyser as there is variation in concentrations when run on different analysers. The trend for an individual patient is more important than the absolute values and all results should be considered in conjunction with clinical signs including examination of home records, laboratory results including glucose monitoring and urinalysis and response to current treatment. There is significant variation between an individual’s fructosamine levels e.g. a well-controlled patient can have a higher level than a poorly controlled patient. Fructosamine concentrations can be decreased in cats with hypoproteinaemia and uncontrolled hyperthyroidism and in dogs with hypoalbuminaemia, hyperlipidemia and azotaemia, which can impact clinical decision making. Fructosamine concentrations can be increased in dogs with untreated hypothyroidism and in a small population of sick non-diabetic cats. Fructosamine should be measured on serum samples and haemolysed samples are not suitable for fructosamine analysis.

How have the Fructosamine reference intervals changed?

The new reference interval for cats is now 137-286 µmol/L (previously 0 to 340 µmol/L).
The new reference interval for dogs is now 177-314 µmol/L (previously, 187 to 386 µmol/L).

Why has the method for measuring Fructosamine and the associated reference intervals changed?

There has been a global change in the reagents used to measure fructosamine in reference laboratories. As a result, there has been a need to validate the new reagents and critically assess current reference intervals considering the new methodology. IDEXX has validated the new reagents and generated appropriate reference intervals utilizing surplus blood from blood donor dogs and wellness testing in cats. These reference intervals will be continuously reviewed as more samples are analysed.

How was the new reference interval established?

Healthy blood donor samples were used to establish the reference interval for dogs in the UK. This reference interval is comparable to that established in the USA with the same methodology. Ongoing assessment is taking place looking at the possible impact of dog breeds/size on the reference interval, although a recent study² showed that whilst there were inter-breed differences in fructosamine results, all breeds remained within previously established reference intervals.
The feline reference interval was established following analysis of surplus serum samples from clinically healthy cats (pre-anaesthetic/wellbeing screens with full haematology/extended biochemistry including thyroxine where results were all within normal limits).

How can I compare results generated using the old method with results generated using the new method?

Our new reference intervals offer the most appropriate context for interpretation of an individual’s fructosamine result. Serial measurement from the same patient to produce a trend in fructosamine results is more important than a single measurement. We have evaluated samples from dogs and cats using the current and the new methodology. The new method produces lower results. Therefore, when comparing a result from before June 24th, 2019 with a current result the following calculation may be used:

• Dog – subtract 70 µmol/L from the old result
• Cat – subtract 40 µmol/L from the old result
   

Can I compare Catalyst Fructosamine results with reference laboratory Fructosamine results?

It is important when making comparisons between results, and assessing trends, that the result is generated not only by the same methodology but most importantly by the same type of analyser/machine. Therefore, we would advise that trends in fructosamine, which is the best way to use the test, are assessed on results generated from the same source i.e. either in-house or reference laboratory and not a combination of both.

How will the interpretation of Fructosamine results be affected by the change in the reference range of Fructosamine?

The interpretative guidelines for fructosamine are being continuously reviewed and adjusted in line with the change in the reference interval and current consensus statements (2018 AAHA Diabetes Management Guidelines for Dogs and Cats).³ It is important to note that fructosamine results in the normal reference interval in diabetic patients usually indicate that there may be periods of hypoglycaemia and a need to review the patient history and results to see if this is likely. Fructosamine results >450 µmol/L can suggest poor control and the need to review the patient.

The trend for an individual patient is more important than the absolute values and all results should be interpreted in conjunction with clinical history (including home records), clinical signs, changes in body weight, laboratory findings and response to current treatment.

Our team of internal medicine consultants will be on hand to help guide our clients through this important transition and we would encourage people to utilise this excellent free service.

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