Fructosamine test vs HbA1c test

The Fructosamine and the Hemoglobin A1c (HbA1c) tests for diabetes both measure blood sugar, but there are differences.

What is the Fructosamine test?

The Fructosamine test measures average blood sugar levels across a two-to-three week time frame and the HbA1c test measures across a three-month time frame prior to the test date.

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

What is the HbA1c test?

The HbA1c test, on the other hand, measures glycated hemoglobin (red blood cells) during the lifetime cycle of the red blood cells, which is around 90 days. Understanding the HbA1c test and what the levels mean for you are crucial to achieving better health and overall wellness.

While the HbA1c 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 HbA1c tests, and why each may be used. It explains what the results mean and how you can convert the test results from Fructosamine to HbA1c.

How The Fructosamine Test Works

  1. Glucose sticks to proteins in the blood
  2. Proteins circulate in bloodstream for 14-21 days
  3. Test measures average blood sugar levels over that time


Purpose of the Fructosamine Test

Unlike the HbA1c test, the Fructosamine test is not used as a screening test for people who may have risk factors for diabetes, or for those who have well-controlled diabetes.  Instead, the Fructosamine test may be used in situations in which the HbA1c test is less reliable or doesn’t offer the same information.

Advantages 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 medications, as it can help gauge the effectiveness of the new treatments in a more immediate time window.  Given this information, you, along with your healthcare team, can make educated, quick adjustments to your medication treatment plan.

The Fructosamine test may also be used during pregnancy when your body is changing constantly. HbA1c testing during pregnancy has been shown historically to lead to false low results, so, the Fructosamine test would be a much more accurate test during the nine months of pregnancy. Fructosamine may also 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 HbA1c results less reliable.

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

  • Hemolytic Anemia or recent blood loss: Because of the rapid turnover of your red blood cells, an HbA1c test result may give a false low reading
  • Sickle Cell Anemia: An inherited form of anemia where the red blood cells change from the normal round (similar to a doughnut) shape to a long pointed shape like a sickle or banana.  These sickled red blood cells have difficulty flowing through the blood vessels and can get stuck. The body recognizes these red blood cells as abnormal and destroys them faster than usual resulting in anemia
  • Kidney Disease(End-Stage Renal Disease): The primary functions of the kidneys are to excrete waste and regulate the water and acid-base balance of the body. Without these functions, a person cannot survive.
  • HIV Infection: A virus that causes acquired immunodeficiency syndrome (AIDS). HIV is transmitted via blood, semen, and vaginal fluids and causes a range of symptoms that present soon after infection, including fever and swollen glands. After a latent period—during which HIV progresses to AIDS (HIV/AIDS)—those infected are faced with more serious concerns, including extreme weight loss and opportunistic infections.
  • Blood Transfusion: Transfusions are needed if you can’t make enough blood cells or if you lose too much blood at once, during a car accident, for example.


Fructosamine, the HbA1c Test, and Race

Use of the Fructosamine test may also be more beneficial for considerations based on race and ethnicity. The HbA1c test results typically show higher levels in African American, Asian, and Hispanic populations when compared with tests in White/Caucasian populations even if their blood sugar levels are the same. The HbA1c test, therefore, has raised concerns over potential misdiagnoses.  For this reason, additionally adding the Fructosamine test for these populations may be helpful.

Disadvantages of The Fructosamine Test

Some healthcare providers may be moving away from the Fructosamine test because of its limitations, including inaccuracy in assessing long-term complications of diabetes. Also, health conditions that affect Albumin production (protein made by the liver) such as thyroid disease, Cirrhosis of the liver, and smoking can affect the reliability of Fructosamine tests. In addition, high levels of Vitamin C taken within 24 hours of the Fructosamine test may interfere with the reliability of the results.

How the Fructosamine Test Is Done

The Fructosamine test is a simple blood test done with a sample drawn from a vein or finger stick at your healthcare provider’s office and analyzed in a laboratory using certified and standardized methods.  It is usually covered by health insurance.  Risks are minimal, as with any blood draw, and no special preparation (e.g., fasting) is required. Home-based Fructosamine tests were discontinued in 2002 because they were shown to be too inaccurate in its results.

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:

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

The mmol/L measurement is primarily used in countries outside of the United States. In the US, it is more common to record measurements using Mg/dL (milligrams per deciliter). By multiplying the mmol/L measurement by 18, you can convert it to Mg/dL.

High Fructosamine levels indicate high average blood sugar 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 HbA1c testing every three months.

If the results remain high, it shows you have not had good blood sugar control. It is at this point where your healthcare team (Certified Diabetes Educator, Registered Diabetes Nutritionist) will try to determine the cause and help you adjust your diabetes management plan, including medication adjustment, nutritional changes, and changes in your daily moderate exercise routine.

This also applies to consistently low blood sugar levels (hypoglycemia), which can be very dangerous, especially with the elderly, as hypoglycemia can contribute to dizziness, fainting, and accidents due to falls.

Reference Ranges for HbA1c

Fructosamine results may be considered alongside the HbA1c tests. The reference ranges for HbA1c results are:

  • No diabetes: below 5.7%
  • Borderline/Prediabetes: 5.7% to 6.4%
  • Diabetes: 6.5% or higher

Converting Fructosamine to HbA1c

One formula used to convert Fructosamine to HbA1c uses the Fructosamine level value (the mmol/L) x 0.017 + 1.61 to arrive at the HbA1c value (percentage).

Comparison of HbA1c and Fructosamine tests

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

Some examples of how Fructosamine levels would work in real life, include results of:

  1. An HbA1c of 6.5% and Fructosamine level of 244 leading to an original diagnosis of diabetes
  2. An HbA1c of 7.5% and Fructosamine at 409, during an episode of Diabetic Ketoacidosis (DKA), a potentially life-threatening complication of diabetes where the liver starts breaking down fat at a dangerously fast rate, processing the fat into a fuel called ketones, which causes a diabetic person’s blood to become acidic
  3. An HbA1c of 11.9% and Fructosamine of 408, with medications, such as Metformin, used rather than insulin in a person with newly diagnosed type 2 diabetes

A Fructosamine test and an HbA1c test are likely to be part of a larger group of tests your healthcare team 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 use this knowledge as power. Use your test results to motivate you to learn more about your diabetes.  With a sound diabetes management plan created by your dedicated care team, including nutrition, medication, and other lifestyle changes, such as exercise, you can be sure you will see consistent progress and improvement the next time you are tested.

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