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HbA1c, Fasting Blood Glucose, or Both

Are two better than one at predicting diabetes?…

Data from 1,690 adults without diabetes on baseline impaired fasting glucose (IFG) and elevated HbA1c levels were gathered from the longitudinal Health ABC study. IFG was defined as 100-125mg/dL and elevated A1c was defined as 5.7-6.4% per American Diabetes Guidelines. Follow-up was done for the next 7 years to record any incidents of diabetes. Incidences were determined by self-report, use of antihyperglycemic medication, or HbA1c ≥6.5%. Two models were compared; IFG levels were compared with normal FPG and elevated HbA1c was compared with normal HbA1c. Odds of diabetes associated with both IFG and elevated HbA1c were found using a model with three dummy-coed variables: IFG only, Elevated HbA1c only, and both compared to the reference group that had neither. 

Out of all the included participants, 183 (10.8%) developed diabetes by the end of the follow up period. The odds ratio of diabetes in patients with IFG only versus normal IFG (<100mg/dL) was 6.2 with 28.2% of these patients developing diabetes. The odds ratio of diabetes in patients with elevated HbA1c versus normal HbA1c (<5.7%) was 11.3 with 33.2% of these patients developing diabetes. When both of these were examined together the odds ratio changed a little bit. For IFG only it was 3.5, for elevated HbA1c only it was 8 and having both IFG and elevated HbA1c the odds ratio was 26.2.

Researchers concluded that older adults having both IFG and elevated HbA1c levels at baseline have increased odds of developing diabetes over 7 years. Impaired fasting glucose has been the traditional method for identifying patients at risk, and elevated HbA1c has slowly been introduced to guidelines. This research suggests that doing screening for BOTH can help find those older adult patients with a high risk.

Lipska, K. et al. Elevated HbA1c and Fasting Plasma Glucose in Predicting Diabetes Incidence Among Older Adults. Diabetes Care;36(12):3923-3929. December 2013