Fructosamine: a Potentially Useful Surrogate

Your patient is a 56-year-old African American woman with suboptimally controlled type 2 diabetes mellitus. She also has chronic kidney disease and anemia of chronic disease. Because of her renal insufficiency, hemoglobin A_1c (HbA_1c) measurement is not reliable. What test would you use in its place?

Fructosamine is formed by non-enzymatic glycosylation of proteins in the serum, mainly by albumin, the most abundant extracellular protein in plasma.¹ Albumin accounts for approximately 80% of all fructosamine. The serum fructosamine level usually indicates the extent of glycemic control for the past 14 to 21 days; this period is also the half-life of serum albumin.¹

Fructosamine is not commonly employed in monitoring glucose control but may be a useful surrogate test in the following scenarios:²

• When determining glycemic control during a narrow interval, such as evaluating glycemic control in pregnant women with diabetes

• Assessing glycemic control in patients with large or rapid fluctuations in glucose

• Gauging the effects of short-term changes in medications, exercise, or diet more rapidly than an HbA_1c value (a few weeks versus 2 to 3 months)

• Obtaining this laboratory test instead of HbA_1c in patients who have conditions associated with decreased red blood cell lifespans, such as anemia of chronic disease, hemoglobinopathy (such as sickle cell anemia), or hemolytic anemia

Keep in mind that these conditions may weigh against obtaining fructosamine:

• Hyperthyroidism

• Nephrotic syndrome

• Conditions that result in decreased protein production (such as cirrhosis)

Here are some important and interesting points to consider.

1. Is there a standard reference range for fructosamine?

No, and this is what can render this test difficult to interpret. This equation may be helpful to convert, and the following is likely the only math you’ll ever see in my posts:

HbA_1c = 0.017 ^_X Fructosamine + 1.61

2. Can fructosamine be used to diagnose diabetes?

No, since the levels in persons without diabetes may be similar to those in patients with diabetes whose levels are at goal.

3. How do you interpret a normal fructosamine level in a patient with diabetes?

The short answer: it can be challenging; a number within the normal range points to good control. It’s not so much the number, but the trend.

References:

1. Danese E, et al. Advantages and pitfalls of fructosamine and glycated albumin in the diagnosis and treatment of diabetes. J Diabetes Sci Technol. 2015;9:169-176.

2. Kotus J. Fructosamine. January 13, 2014. http://emedicine.medscape.com/article/2089070-overview. Accessed April 9, 2017.