Differences Between Glycemia Estimates from Hemoglobin A1c and Continuous Glucose Monitoring and Their Association
Veronica Tozzo1,2,3, David M Nathan4,5, Heidi Krause-Steinrauf6
1Department of Pathology and Center for Systems Biology, Massachusetts General Hospital, Boston, Massachusetts, USA.
Objective:
Continuous glucose monitoring (CGM) and hemoglobin A1c (HbA1c) provide estimates of mean glycemia that may differ, in part, due to the effects of variation in red blood cell (RBC) age and turnover on HbA1c. Measurements derived from the complete blood count (CBC) may vary with RBC age and might be used to reduce the difference between glycemia estimates derived from CGM and HbA1c.
Methods:
We analyzed CBC measurements from 1,325 individuals with type 2 diabetes who participated in the Glycemia Reduction Approaches in Diabetes: A Comparative Effectiveness Study (GRADE) CGM substudy. Mean glycemia was estimated from HbA1c (eAGA1c) using the A1c-Derived Average Glucose (ADAG) formula and from CGM by averaging 10 days of measurements (eAGCGM). We evaluated the association between CBC-derived data and the difference (eAGA1c - eAGCGM) using linear models, both unadjusted and adjusted for age and self-identified sex.
Results:
In adjusted analyses, several CBC-derived measurements were significantly associated with the difference between eAGA1c and eAGCGM. Platelet count and RBC distribution width (RDW) were positively associated, while hemoglobin concentration (HGB), reticulocyte fraction, mean corpuscular volume (MCV), mean corpuscular hemoglobin content (MCH), mean corpuscular hemoglobin concentration (MCHC), and reticulocyte MCHC were negatively associated. A linear model from HbA1c to eAGCGM adjusted with all significantly associated CBC measurements (CBCall-AGA1c) provided modestly improved estimates of eAGCGM compared with ADAG, with R2 (SD) for ADAG of 0.68 (0.07) and for CBCall-AGA1c 0.72 (0.06).
Conclusions:
CBC measurements are associated with differences between estimates of glycemia derived from HbA1c and CGM. Further studies with longer periods of CGM are needed to determine whether CBCs can complement HbA1c and CGM and can help reconcile differences in estimates of mean glycemia provided by HbA1c and CGM.
