Accuracy of HbA1c Test Challenged

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A problem for diabetic hemodialysis patients.

 

The gold standard for measuring glucose control, the hemoglobin A1c (HbA1c) test, may be inaccurate in diabetic patients on hemodialysis, according to a new study.

 

“These results suggest that the more than 200,000 diabetic hemodialysis patients in the United States who use this test may not be receiving optimal care for their blood sugar,” said senior author Barry Freedman, MD, professor of internal medicine and Chief of the Section on Nephrology at Wake Forest University Baptist Medical Center in Winston-Salem, N.C. “The test we've all come to accept as the gold standard has proven to be inaccurate in this patient population.”

 

He and his colleagues evaluated 307 patients with diabetes of whom 258 were on hemodialysis and 49 were without kidney disease. The HbA1c test was compared with the newer glycated albumin (GA) test. GA is believed to more accurately reflect glycemic control in diabetic hemodialysis patients than the HbA1c because of shortened red blood cell survival. 

 

GA measures the amount of blood sugar that has reacted with albumin. The GA test reflects blood sugar control over the previous three to four weeks. The GA test is not currently available in the United States.

 

In diabetic subjects on hemodialysis, compared to those with normal kidney function, the mean GA concentrations and average blood sugars were both significantly higher; whereas HbA1c levels tended to be lower. The GA to HbA1c ratio was also significantly increased in diabetic hemodialysis patients compared with non-kidney disease controls. HbA1c levels were positively associated with hemoglobin levels and negatively associated with the dose of erythropoietin in hemodialysis patients. However, these factors, and serum albumin, had no significant impact on GA levels.

 

Overall, in diabetic hemodialysis patients, HbA1c levels significantly underestimate glycemic control, the investigators concluded in Kidney International (2008; published online ahead of print).

 

“I was surprised by the magnitude of these results,” Dr. Freedman told Renal & Urology News. “Initially, our group did not expect to see such marked differences between the two measures of glycemic control. Although I expected to detect modest variation between these tests, the dramatic differences that were observed are clearly clinically important and will impact patient care. The glycated albumin test is currently available in Japan.

 

Now that this study is complete, Asahi Kasei Pharma Corporation, the manufacturer of the GA test, may apply for approval to make it available in the U.S. The GA appears to be a better measure of blood sugar control in the diabetic hemodialysis population than the HbA1c.”

 

It is theorized that the discrepancy found in the study is due to the fact that HbA1c depends on red blood cell survival and these cells do not live as long in patients on hemodialysis. This new study confirms a prior report in Japanese patients and is the first to demonstrate the inaccuracy of the HbA1c in diabetic African-American and Caucasian dialysis patients in the United States. The researchers now plan to conduct a similar study in patients on peritoneal dialysis and with chronic kidney disease not yet on dialysis.

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