Next, another straight forward report, this time on diabetes. David Nathan et al from the Joslin Diabetes Center reported in the August 31st issue of Diabetes Care, their study “Translating the A1C Assay into Estimated Average Glucose Values.” Their study essentially defines the mathematical relationship between A1C and average glucose. The obvious and practical need for this is obvious: patients understand “average glucose” much better than a number that tells them the “amount of hemoglobin that is glycosylated.” How many times have you found yourself explaining exactly what HgA1C means only to have a patient respond by telling you that their sugar never goes above 120? With Dr. Nathan’s study, you might realistically be able to tell a patient what their “AG” or “average glucose” is. The other pressing importance of this study is that a new, more stable and specific method for standardization of the A1C assay has been developed. Values are lower and units are different than our current A1C assays. Thus, rather than learn a new system for reporting a non-so-helpful number, why not convert it? In the study, approximately 500 patients had their glucose monitored by two methods: continuous glucose monitoring and sever-point daily self monitoring. Many, many glucoses were obtained on these 500 patients and a linear regression analysis was conducted. The table below is the result:
A1C % AG* mg/dl
5 97 (76-120)
6 126 (100-152)
7 154 (123-185)
8 183 (147-217)
9 212 (170-249)
*AG=average glucose
The limitations of the study include the relative lack of representation of minorities, including Asian and African Americans. Nonetheless, it’s thought that the mathematical relationship is sound regardless of ethnicity and age. The importance of this is underscored by its inclusion in the most recent consensus statement on hemoglobin A1C measurement.
