What Is a Fructosamine Blood Test for Diabetes?

The fructosamine test is similar to the hemoglobin A1c test, but it is not as commonly used.

The main difference between the two tests is that the fructosamine test measures your average blood glucose level over the past two or three weeks, while the A1c test is a measurement average of your blood sugar over the past two to four months.

In addition, the fructosamine test measures glycated protein in the blood, instead of glycated hemoglobin. Sugar molecules that are present in your blood stick to proteins. These proteins circulate in your bloodstream for 14 to 21 days, so measuring them provides a picture of the amount of sugar in your blood for that time period.

Unlike the A1c test, the fructosamine test is not used as a screening test for people who do not have diabetes or who have well-controlled diabetes.

Instead, the fructosamine test is used when the A1c test cannot provide reliable monitoring.

A number of conditions can affect HbA1c levels. For example, if you have had blood loss or hemolytic anemia, the rapid turnover of your red blood cells will mean that testing hemoglobin A1c will be falsely low, so a fructosamine test will be more accurate. If you have sickle cell anemia or other hemoglobin variants, the hemoglobin A1c test is also less reliable and the fructosamine test may be preferred.

Other conditions that may affect HbA1c reliability include kidney failure (end-stage renal disease), liver disease, HIV infection, and having undergone recent blood transfusions.

The fructosamine test is also used when you want more information. It is used as an addition to blood glucose logging when you've had a recent change in your medicines or insulin and can help to monitor the effectiveness of the new treatments after just a few weeks rather than waiting months to do an A1c test. The test may also be used during pregnancy when your body is changing constantly.

Some doctors may be moving away from the fructosamine test. A 2016 review concluded the test doesn’t have enough evidence to support its use. The authors note a different test that measures glycated albumin—which also reveals blood sugar levels over the short term—shows promise in most accurately identifying prediabetes in African-Americans and those who are not obese. Another 2015 article noted that glycated albumin testing is considered more reliable than fructosamine testing.

This is a blood test done with a sample drawn from a vein or fingerstick at your doctor’s office and analyzed in a laboratory. Risks are minimal, as with any blood draw, and no special preparation, such as fasting, is required. A home-based test was discontinued in 2002 because it wasn't accurate. It is usually covered by health insurance.

High fructosamine levels indicate high average blood glucose levels took place in the previous two to three weeks. Usually, a trend is monitored with repeat testing, whether of fructosamine levels or other indicators, such as glycated albumin or HbA1c. If the results remain high, it shows you have not had good blood glucose control. Your doctor will try to determine the cause and help you adjust your medications, diet, and other factors to maintain better control.

While it's still not entirely clear what fructosamine levels indicate and how they correlate to diabetes or its complications, the following guide is suggested by some authorities.

• For people without diabetes, the fructosamine range is 175-280 mmol/L.
• For people with controlled diabetes, the fructosamine range is 210-421 mmol/L.
• For people with uncontrolled diabetes, the fructosamine range is 268-870 mmol/L.

Sometimes, the reliability of the fructosamine test can be compromised. Any condition that affects serum albumin production, either increasing or decreasing turnover, may affect the reliability of the fructosamine test. Some examples of these conditions include:

• Liver diseases (e.g., cirrhosis)
• Nephrotic syndrome
• Thyroid disease
• Paraproteinemia

In addition, high levels of ascorbic acid (vitamin C) can interfere with the reliability of the test. Therefore, patients should abstain from ascorbic acid supplements for a minimum of 24 hours prior to sample collection. The Chinese herb Polygalae Radix is biologically similar to 1,5-AG and may also affect results.

A fructosamine test is likely to be part of a larger group of tests your doctor orders. Take your time to review your results, and be sure to ask questions about anything you don’t understand. Getting test results can be worrisome but remember there are many easy ways you can take control of your blood sugar with diet, medication, and other lifestyle changes, such as exercise. Use this opportunity to learn about diabetes, make simple changes, and you should see improvements at your next test.