Fructosamine

Glucose in the blood slowly sticks to proteins. Fructosamine is the collective name for these sugar-coated (glycated) proteins in the blood, mainly glycated albumin. Because these proteins last about two to three weeks, fructosamine reflects the average sugar level over that period. Unlike a single glucose measurement, which only shows the moment of the blood draw, this is therefore an average over several weeks.

• An average blood sugar that has been too high over the past 2 to 3 weeks
• The short-term effect of a change in diabetes treatment

With a raised value, the GP usually measures a fasting glucose and an HbA1c before drawing a conclusion. With known diabetes, the treatment is adjusted if needed and checked again after a few weeks. With a strikingly low value, the GP looks at the albumin and at liver and kidney function.

Fructosamine gives an average over two to three weeks; HbA1c does so over about six to eight weeks. For HbA1c, the meaning and the target values have been well studied and are set out in the Dutch GP guideline (NHG) on type 2 diabetes mellitus; for fructosamine there are no agreed target or cutoff values. Fructosamine is mainly informative when HbA1c is unreliable because the red blood cells live shorter, for example with some blood diseases, with an abnormal form of hemoglobin, after bleeding or a transfusion and during pregnancy. Fructosamine has not been studied for, and is not suitable for, determining whether someone has diabetes.

• The result depends strongly on the protein concentration in the blood: with a low albumin it comes out too low, with a high albumin too high.
• A rapid change in blood sugar over the last few days is not yet visible; the value lags two to three weeks behind.
• There are no Dutch target or cutoff values; reference values differ per laboratory and between people with and without diabetes.
• High vitamin C intake, a strongly raised bilirubin and strongly raised blood fat levels can disturb the measurement.

In the Netherlands about 1.2 million people have diabetes, by far most often type 2, and the number rises with age. How often an abnormal fructosamine occurs is not registered.

The test can be useful in people with diabetes in whom HbA1c does not give a reliable picture, for example with a shortened lifespan of the red blood cells, an abnormal form of hemoglobin, after bleeding or a transfusion and during pregnancy. It can also show the effect of a recent change in treatment sooner than HbA1c. In people without diabetes and without symptoms, the result says little: for diagnosing diabetes, a fasting glucose and HbA1c are the studied measures.

• A low value due to a low albumin can make blood sugar control wrongly seem reassuring.
• Because Dutch target values are lacking, a slightly abnormal result is hard to interpret and can cause unnecessary worry.

• NVKC, allesovertesten.nl: Fructosamine
• NVKC, allesovertesten.nl: HbA1c
• NHG-Standaard Diabetes mellitus type 2 (M01)
• Thuisarts.nl: Ik wil mijn diabetes type 2 goed controleren