NEW ORLEANS – Suspect a problem with the hemoglobin A1c whenever it’s discordant with blood sugar–monitoring data.
This happens surprisingly often. The HbA1c level is a measure of glycolated hemoglobin, so any condition that affects hemoglobin, either qualitatively or quantitatively, can seriously distort the HbA1c value, Dr. Thomas L. O’Connell explained at the annual meeting of the American College of Physicians.
Dr. Thomas L. O'Connell
Examples include patients on hemodialysis, or who have recently been transfused, are anemic, or who have a hemoglobinopathy, noted Dr. O’Connell, an endocrinologist at Duke University, Durham, N.C.
"Don’t even bother measuring [HbA1c] in a patient who has recently been transfused. This happens all the time in the hospital: a transfused patient’s blood sugar level on finger-stick testing is 300 mg/dL, but the [HbA1c] is 5.5%," he observed.
Hemoglobinopathies can result in either a false-high or false-low HbA1c value. More than 700 hemoglobinopathies or abnormal hemoglobin variants have been described and many of these are asymptomatic. The most common hemoglobinopathy in the United States is sickle cell trait, affecting 2 million people.
"There are a lot of people out there with hemoglobinopathies," the endocrinologist stressed.
When the HbA1c results seem sketchy, an excellent alternative is the fructosamine test. Not nearly as well known as the HbA1c, the fructosamine test measures glycolated protein in the blood rather than glycolated hemoglobin, so it is unaffected by hemoglobinopathies.
If blood glucose measurement by fingerstick provides a snapshot of a patient’s diabetic control and the HbA1c is more like a feature-length movie reflecting metabolic control over the past 3 months, then the fructosamine test is akin to a short film providing a view of a patient’s average blood glucose concentration during the previous 2-3 weeks.
Dr. O’Connell reported that he serves as a consultant to Sanofi-Aventis and Amylin.