Hemoglobin A1c underestimates glucose concentrations in sickle cell trait

By Will Boggs MD

NEW YORK (Reuters Health) – Hemoglobin A1c underestimates fasting and 2-hour glucose levels in African Americans with sickle cell trait, according to a retrospective cohort study.

"We were most surprised by the finding that, when using standard A1C cutoffs to screen for disease prevalence, we identified 40% fewer cases of prediabetes and 48% fewer cases of diabetes in individuals with sickle cell trait than in those without sickle cell trait,” Mary Elizabeth Lacy from Brown University School of Public Health, Providence, Rhode Island told Reuters Health. “To me, this finding really underscores the potential clinical impact that the observed underestimation of A1C in those with sickle cell trait could have.”

Red blood cells from individuals with sickle cell trait contain 30% to 40% hemoglobin S, which appears to result in a shorter lifespan for red blood cells. This, in turn, means less available time for hemoglobin glycation, which may influence the interpretation of HbA1c in relation to the glucose values it represents.

Lacy and colleagues examined the association between sickle cell trait (SCT) and HbA1c for given levels of fasting or 2-hour glucose levels in their study of 4620 African American individuals (367 with SCT).

The mean HbA1c level was 5.7% in those with SCT, compared with 6.0% in those without SCT, despite similar mean fasting and 2-hour glucose values, according to the February 7th JAMA report.

Among participants with no prior diagnosis of diabetes or current use of diabetes medication, the prevalence of prediabetes and diabetes did not differ between individuals with and without SCT when defined using fasting glucose or 2-hour glucose.

When defined using HbA1c levels, though, the prevalence of prediabetes was 29.2% with versus 48.6% without SCT, and the prevalence of diabetes was 3.8% with versus 7.3% without SCT.

HbA1c was significantly less able to identify the presence of prediabetes or diabetes among participants with SCT than without SCT whether they were defined by fasting glucose or 2-hour glucose.

SOURCE: http://bit.ly/2ln3Rap

JAMA 2017.

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