NEW YORK (Reuters Health) - Measuring patients' glycosylated hemoglobin levels (A1C) could be used to screen for diabetes, according to California-based researchers.

A1C is a test that measures the percentage of glucose (sugar) that is attached to hemoglobin, a molecule in red blood cells. It reflects the average glucose levels over the previous 3 to 4 months. Untreated (or uncontrolled) diabetics have A1C levels that are 7.0 percent or higher. Diabetes is also detected by fasting plasma glucose levels of 126 milligrams per deciliter (mg/dL) or greater.

"Currently, fasting plasma glucoses are recommended to screen for -- and possibly diagnose -- diabetes," senior investigator Dr. Mayer B. Davidson told Reuters Health. "Few physicians are doing this, because most patients are seen during the day, after they have eaten. A1C measurements do not require fasting and can be measured at a routine office visit."

To determine what A1C levels should lead to further testing for diabetes, Davidson of the Charles R. Drew University, Los Angeles and colleagues studied data from 4,935 participants in the 1999-2004 National Health and Nutrition Examination Survey.

Based on fasting plasma glucose levels, 3,280 subjects were normal, 1,485 had pre-diabetic levels (100 to 125 mg/dL) and 170 had previously undiagnosed diabetes (126 mg/dL or higher), the researchers report in the journal Diabetes Care.

Patients with A1C levels of less than 5.8 percent, said Davidson, "will be unlikely to have diabetes and those with 5.8 percent or above will be much more likely. Thus, only a minority of patients will have to return fasting for either a glucose measurement or a full oral glucose tolerance test."

"This should increase the early diagnosis of diabetes so that appropriate treatment can be instituted to prevent the complications of the disease," he concluded.