The hemoglobin A1c test (HbA1c) is a staple among people with diabetes attempting to map out their long-term blood glucose levels. However, it is not a standard test for non-diabetics, even those whose doctors suspect they may have the disease.

But that could change soon. Dr. Christopher Saudek, a professor of endocrinology at the Johns Hopkins University School of Medicine and director of the school’s Comprehensive Diabetes Center, says that the A1c test is far better than the diagnostic tools doctors currently use to detect diabetes and should be used in place of them.

At stake, he says, is the fact that up to 6 million Americans may have diabetes that current tests have failed to detect.

Dr. Saudek and five other diabetes researchers recently wrote a consensus statement calling for their peers to use the A1c instead of the fasting glucose and oral glucose tolerance tests that most doctors currently use to detect diabetes.

The problem with those tests, says Dr. Saudek, is that they measure only the blood sugar present at the moment a blood sample is drawn—a figure that can be skewed by recent food intake or exercise.

For example, the fasting glucose test requires patients to fast for at least 10 hours before taking the test. The idea is that the body will have metabolized blood sugar to a level that is consistent with, say, a patient’s level upon rising in the morning. The problem is that many patients fail to actually fast, resulting in inaccurate data that can lead to a misdiagnosis.

In other cases, says Dr. Saudek, patients step up their exercise and activity days before taking a test. While this temporarily lowers their blood glucose levels—a beneficial effect—it hides the higher readings that could lead a doctor to suspect diabetes.

The advantage of the A1c is that it tracks blood glucose levels over a 120-day period, providing a long-term view that takes blood glucose spikes and dips into account without making them the primary focus.

In a way, the A1c is like grading on a curve—the highest and lowest scores are thrown out, and the remaining mean offers the most accurate picture of a patient’s overall blood glucose levels.

According to Saudek and his associates, doctors who begin routinely administering A1c’s to their patients should categorize those who score 6% on the test as pre-diabetic and track them. Patients who score 6.5% or more should be considered diabetic and entered into treatment for the disease.

An abstract of the study by Dr. Saudek and his colleagues can be found in the July 2008 issue of the Journal of Clinical Endocrinology and Metabolism.