Categories of increased risk for diabetes:

• A fasting blood sugar level of 100 to 125 milligrams per deciliter (mg/dL) after an overnight fast, OR
• A 2-hour blood sugar level of 140 to 199 mg/dL after a 2-hour oral glucose tolerance test (OGTT), OR
• An A1c level of 5.7% to 6.4%.

All of these tests identify people at risk of developing diabetes. For all 3 tests, the risk of diabetes is not the same throughout the range of results. Risk for developing diabetes is lower in those who fall at or below the lower limit and is higher in those with results at the upper end of the range. However, the number of people that these tests identify and their characteristics vary between the 3 tests. For example, A1c varies by race/ethnicity independent of blood glucose levels. Research is ongoing to ascertain the best use of laboratory blood tests to detect people who may have prediabetes and to improve the understanding of who has prediabetes
(http://www.ngsp.org/CAC2009.asp).