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Self-monitoring of blood glucose (SMBG) is one of the two primary techniques available for health providers and patients to assess the effectiveness of the management plan on glycemic control in diabetes. SMBG is typically carried out in the form of frequent fingerstick capillary glucose testing. Another more recent technology available is continuous glucose monitoring (CGM) carried out through a sensor that measures interstitial glucose concentration which correlates well with plasma glucose and capillary glucose levels. The second glycemic control technique is measurement of hemoglobin A1c (Hb A1c).
Because measurement of Hb A1c is primary, the most accurate glycemic control tool available, it is important to correlate Hb A1c results with ones obtained using SMBG for long-term metabolic control and management of diabetes. Recently, the international multicenter A1c-Derived Average Glucose (ADAG) trial successfully completed and results determined that the correlation between Hb A1c results and eAG (the new term used to combine both CGM and fingerstick capillary glucose testing) is strong enough to justify reporting of both an Hb A1c results and eAG result. This conclusion is endorsed by the American Diabetes Association (ADA) and the American Association of Clinical Chemists. The relationship is expressed in the following formula:
eAG(mg/dL) = 28.7 x Hb A1c(%) - 46.7
This relationship applies only to Hb A1c methods certified as traceable to DCCT reference, and is based on overall averages and may vary slightly in individual patients. LabCorp uses a DCCT traceable method.
Mean plasma glucose estimates outside of the 5.0% to 15.0% Hb A1c range are not calculated since estimations in the nondiabetic range have not been verified. Only diabetic patients in stable control and without any suggestion of erythrocyte disorders were entered into the study. Children and pregnant women were also excluded; additional data in these groups are needed to confirm the established relationship. This mean plasma glucose calculation should only be used with Hb A1c (001453). For additional information, see Hemoglobin (Hb) A1c [001453].
American Diabetes Association Clinical Practice Recommendations 2009. Diabetes Care. 2009; 32(Suppl 1):S1-S98. PubMed 9510875
Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose Study Group. Translating the A1c assay Into estimated average glucose values. Diabetes Care. 2008 Aug; 31(8):1473-1478. PubMed 18540046
