Fructosamine Test for Diabetes: Pros, Cons, Compared to A1C

The fructosamine and A1C tests for diabetes both measure blood sugar. But there are differences, with the fructosamine test measuring average blood glucose levels across two or three weeks prior to the test date and the hemoglobin A1C test (HbA1c) measuring across two to four months.

The shorter fructosamine time window is not sufficient for determining a long-term prognosis. The fructosamine test measures glycated proteins (not glycated hemoglobin) that circulate in the blood for only 14 to 21 days. Measuring these proteins provides a picture of the amount of sugar in your blood for just that time period.

While the A1C test is now generally preferred, fructosamine tests are more accurate with certain health conditions and situations.

This article explains benefits and limitations of both the fructosamine and A1C tests, and why each may be used. It explains what the results mean and how you can convert the test results from fructosamine to A1C.

Purpose of the Fructosamine Test

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 may be used in situations in which the A1C test is less reliable or doesn't offer the same information.

Benefits of Fructosamine Test

The fructosamine test may be more useful in certain situations, like managing diabetes in the short term, or with certain health conditions. For example, it may be used if you've had a recent change in your medicines or insulin, as it can help gauge the effectiveness of the new treatments in a more immediate time window.

The test may also be used during pregnancy when your body is changing constantly, which may lead to falsely low A1C results.

Health conditions in which the fructosamine test may offer benefits include:

• Hemolytic anemia or recent blood loss, because the rapid turnover of your red blood cells means a hemoglobin A1C test result will be falsely low
• Sickle cell anemia
• Kidney failure (end-stage renal disease)
• Liver disease
• HIV infection
• Recent blood transfusions

Fructosamine may be a useful test for people who develop gestational diabetes (diabetes during pregnancy) because changes in red blood cells and rapid blood sugar increases can make A1C results less reliable.

Drawbacks of Fructosamine Test

Some healthcare providers may be moving away from the fructosamine test because of its limitations, including accuracy in assessing long-term complications of diabetes. A 2016 review concluded that the fructosamine test doesn’t have enough evidence to support its use.

The authors note that 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.

However, the glycated albumin tests also have limitations. Albumin levels can be affected by other health conditions, including thyroid disease, kidney and liver conditions, or even smoking. Some of these factors also affect fructosamine tests. A 2015 article also noted that glycated albumin testing is considered more reliable than fructosamine testing.

How the Fructosamine Test Is Done

This is a blood test done with a sample drawn from a vein or fingerstick at your healthcare provider's office and analyzed in a laboratory. It is usually covered by health insurance.

Risks are minimal, as with any blood draw, and no special preparation (e.g., fasting) is required.

Normal Range for Fructosamine Test

It's not entirely clear what fructosamine levels indicate and how they correlate to diabetes or its complications, but the following guide is suggested:

• For people without diabetes, the fructosamine range should be 175-280 millimoles per liter (mmol/L).
• For people with controlled diabetes, the fructosamine range should be 210-421 millimoles per liter (mmol/L).
• For people with uncontrolled diabetes, the fructosamine range should be 268-870 millimoles per liter (mmol/L).

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 that is 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 healthcare provider will try to determine the cause and help you adjust your medications, diet, and other factors.

Converting Fructosamine to A1C

One formula used to convert fructosamine to A1C uses the fructosamine level (the mmol/L) x 0.017 + 1.61 to arrive at the hemoglobin A1C as a percentage.

Comparing Fructosamine Results to A1C

Other mathematical equations also may be used, and the numbers may vary depending on a person's overall health, weight, and lifestyle choices like exercise.

Some examples of how fructosamine levels would work in real life, based on four specific case studies, include results of:

• An A1C of 5.6 and fructosamine level of 244 leading to an original diagnosis of diabetes
• An A1C of 7.5 and fructosamine at 409, during an episode of diabetic ketoacidosis occurring five years after diagnosis
• An A1C of 11.9 and fructosamine of 408, with metformin used rather than insulin in a person with newly diagnosed type 2 diabetes

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Other Considerations

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 may also affect results.

A Word From Verywell

A fructosamine test is likely to be part of a larger group of tests your healthcare provider orders. Take your time to review your results, and be sure to ask questions about anything you don’t understand.

Getting abnormal 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 your test results as a motivator to learn more about diabetes and make simple changes so you can see improvement the next time you're tested.