Hemoglobin A1c isn’t the only test in town for looking at a patient’s diabetic control over the long haul. Fructosamine testing can also do the trick, only over a shorter time frame. And it can be used as an alternative for patients with hemoglobin variants or altered red blood cell lifespans that can skew hemoglobin A1c readings.
Rather than measure glycation of hemoglobin, fructosamine testing looks at glycation that occurs with serum protein—mostly albumin, says Bruce Beckwith, MD, chief of laboratory medicine at NorthShore Medical Center, Salem, Mass.
The fructosamine test “is somewhat variably defined,” explains Darryl Erik Palmer-Toy, MD, PhD, director of chemistry at the Regional Reference Laboratories at Southern California Permanente Medical Group, North Hollywood, Calif. “Some assays claim to measure glycated total protein and some claim to measure glycated albumin.”
“Albumin has a half-life of about 17 days contrasted to 120 days for hemoglobin in circulation.” Thus, “you can view fructosamine as an intermediate diabetic control marker. It’s not as immediate as a blood glucose, but not as long-standing as A1c,” Dr. Palmer-Toy says.
Given that fructosamine can provide accurate results for people with variant hemoglobin or altered red blood cell lifespans, why not use it on everyone? The big studies, Dr. Beckwith says, have been done on A1c in defining ranges and targets. And “A1c allows you to have a longer look of 120 days” as opposed to fructosamine.
Also, fructosamine values must be adjusted if serum albumin is low or if there is a high rate of turnover of albumin, as in nephrotic syndrome. So its limitations are similar to those of A1c, Dr. Beckwith adds.
Dr. Palmer-Toy’s lab does fructosamine testing, though in much lower volumes than A1c. The bulk of the testing, he says, is ordered for pregnant women with gestational diabetes.
For a pregnant patient, “it can be handy to have a marker that’s shorter duration, spanning less time than a trimester,” he says. “You want a more immediate measurement of the patient’s integrated glycemic control and can know after a month if you are making a difference.”