Issue 135 Item 1 BMI, A1c and Fasting Glucose, Reduce the Need for Oral Glucose

Using data on body mass index (BMI) and cutoff values for fasting glucose and HbA1c, would greatly reduce the use of the oral glucose tolerance test to identify diabetes. That comes from a study published in the November issue of Diabetes Care.

Dr. Sharon H. Saydah, of Social and Scientific Systems, Silver Spring, Maryland, and colleagues examined the accuracy of using fasting plasma glucose or HbA1c to identify subjects who meet the Diabetes Prevention Program (DPP) criteria for intervention. Criteria include a BMI of at least 24 kg/m, fasting plasma glucose level between 96 and 125 mg/dL, and 2-h glucose level between 140 and 199 mg/dL in an OGTT.

The researchers analyzed data on height, weight, fasting plasma glucose, HbA1c, and 2-h plasma glucose during an OGTT from 2844 subjects representative of U.S. adults between the ages of 40 and 74 years with no history of diabetes. They determined sensitivity, specificity, positive predictive value (PPV), and receiver operator characteristic (ROC) curves for fasting glucose and HbA1c. [abstract]

The team reports that 27.2% of the subjects were eliminated from further testing using BMI less than 24 kg/m as an initial criterion. Of the remaining patients, 41.1% had fasting glucose levels below or above 96 to 125 mg/dL and did therefore not have to be considered for an OGTT. Overall, 10.6% of the subjects met the DPP eligibility criteria for intervention.

When a fasting plasma glucose cutoff of at least 105 mg/dL was applied to individuals with BMI of at least 24 kg/meters squared and fasting glucose levels between 96 and 125 mg/dL, 62.5% of the subjects were eliminated from further testing. The sensitivity of a fasting glucose level of at least 105 mg/dL to identify those with 2-h glucose of between 140 and 199 mg/dL was 56%. The specificity and the PPV were 72% and 17.1%, respectively.

"Similarly, at HbA1c of at least 5.5%, which included 38.3% of participants, the sensitivity of HbA1c to identify the individuals with 2-h glucose level 140 to 199 mg/dL was 60.0%, the specificity was 55.0%, and the PPV was 21.4%," Dr. Saydah and colleagues explain.

They conclude that these finding give a clearer idea of the number of OGTTs and the scope of the screening that would be needed to implement the Diabetes Prevention Program.

Diabetes Care 2002;25:1940-1945.