“The use of HbA1c to diagnose prediabetes and diabetes in iron-deficient populations may lead to a spuriously exaggerated prevalence,” caution the authors of the report in Diabetes Care online February 8.
In the background information in their paper, Dr. Chittaranjan S. Yajnik, at King Edward Memorial Hospital Research Centre in Pune, and colleagues explain that HbA1c concentration depends not only on prevailing glycemia but also the life span of erythrocytes. “Iron deficiency increases erythrocyte survival and therefore disproportionately elevates HbA1c concentrations at a given glycemic level,” they note.
For the current study, the team compared the diagnosis of normal glucose tolerance, prediabetes, and diabetes based on a standard oral glucose tolerance test (OGTT) and on HbA1c concentrations using American Diabetes Association criteria in 116 young adults enrolled in a local longitudinal cohort study. Among this group, 34% were anemic, 37% were iron deficient, 40% were vitamin B12 deficient, and 22% were folate deficient, the authors note.
The prevalence of prediabetes was 7.8% and diabetes was 2.6%, based on the OGTT, while corresponding rates based on HbA1c criteria were 23.3% and 2.6%, the researchers found.
“A total of 24 participants who were normoglycemic by OGTT criteria were misclassified as having prediabetes or diabetes by HbA1c criteria, and 6 prediabetic or diabetic participants were misclassified as normal by HbA1c criteria,” they report.
On further analysis, HbA1c was predicted by not only higher glycemia but also by lower ferritin, the report indicates.
“Our results support a substantial nonglycemic nutritional influence on HbA1c concentrations in young nondiabetic Indians,” Dr. Yajnik and colleagues conclude. “This complicates the use of HbA1c in the diagnosis of prediabetes in nutritionally compromised populations (i.e., more than half of the world’s population).”
Diabetes Care 2012.