New Test For Diagnosis of Diabetes and Pre-Diabetes

Leading diabetes organizations in the U.S., as the American Diabetes Association and others will come out with the guidelines within the next couple of months. They will contain information explaining how to use the A1c test as a diagnostic tool for type 2 diabetes.

This change is coming at a time when the diagnosis of diabetes has increased over 90% among U.S. adults in the past 10 years.  From 4.8 cases per 1,000 population during 1995-97, the number climbed up to 9.1 per 1,000 people in 2005-07 in 33 states.

Right now most doctors use the fasting blood sugar result to diagnose diabetes and prediabetes.  But we know that you can have a normal fasting blood sugar but still have undiagnosed diabetes.  This change will allow us to catch more people with diabetes and they will not have to fast for the test.

The glycated hemoglobin test (HbA1c) or the A1c test has been around for more than 30 years.  It provides average blood glucose over the previous 90 days.  It has become the gold standard test in diabetes care.  But, it has not been used as a way to diagnose a person with diabetes because it was not a standardized test.  Meaning that a 6% in one lab could be an 8% in another lab.  Or that a 6% in one lab is 126mg/dL and a 6% in another lab would be 154mg/dL.  It has only been used to find out how a person with diabetes is doing over the last 90 -120 days.  But that is going to change. The glycated A1c test will soon be used to diagnose diabetes.

The credit goes to the NGSP organization (www.ngsp.org) which has standardized the test.  Now most of the labs are standardized now by NGSP (National Glycolization Standardization Program), which is run at the University of Missouri, Medical Center

The purpose of the NGSP is to standardize glycated hemoglobin test results so that clinical laboratory results are comparable to those reported in the Diabetes Control and Complications Trial (DCCT) where relationships to mean blood glucose and risk for vascular complications have been established. A key component of the program is the Reference Laboratory Network. The network interacts with manufacturers of GHB methods to assist them first in standardizing their methods and then in providing comparison data for certification of traceability to the DCCT.

When we begin to use the A1c result for the diagnosis of diabetes and prediabetes, it will be interesting to see what the diabetes organizations use as the cut-off number.

If they are aggressive then maybe an A1c result of 5% to 6%, which is an average mean blood glucose of 97-126mg/dL., would be used for the diagnosis of prediabetes and an A1c of greater then 6% or 126mg/dL. would be the diagnosis for diabetes.

But past experience says that the numbers will probably be much higher.

We might also use the A1c test result to let patients know their cardiovascular risk.  If we look at the results of the Epic-Norfolk study, which compared people with an A1c of 5% to those with 6%, regardless of diabetes, we see that those with a 6% compared to those with a 5% A1c result, had a 28% increase in cardiovascular death for women and a 26% increase for men.

HbA1c, also called A1C, is a measure of the amount of glucose attached to hemoglobin (Hb) in red blood cells.  The higher the glucose levels over the previous 2-3 months, the higher the A1C.  The A1C test is currently used to monitor the glucose levels of patients who have been diagnosed with diabetes.  In people who have hemoglobin variants such as HbS (sickle cell trait), some A1C tests give falsely high or low readings that can lead to the over-treatment or under-treatment of diabetes. 
The landmark nine-year Diabetes Control and Complications Trial (DCCT), completed in 1993, showed that the risk for development and progression of the chronic complications of diabetes is closely related to the degree of glycemic control, as measured by glycated hemoglobin (GHB) determinations (5). The DCCT also provided a large body of data relating GHB values to mean blood glucose. Thus, the DCCT results have set the stage for establishing specific diabetes treatment goals using GHB as an index of mean blood glucose. However, the fact that GHB assay methods have not been standardized among laboratories has prevented optimal use of the test.

The only other test that we use for the diagnosis of diabetes is the Oral Glucose Tolerance Test, which can take up to 3 plus hours to complete.

The 3 people mainly responsible for NGSP are:

David Sacks, M.D.
Chair, NGSP Steering Committee
Brigham and Womens' Hospital
Thorn, Boston, MA 02115

Randie R. Little, Ph.D.
NGSP Network Coordinator
Departments of Pathology and Child Health, Rm M767
University of Missouri School of Medicine, Columbia, MO 65212

David Nathan, M.D.
Massachusetts General Hospital, Boston, MA 02114

Diabetes in Control will keep you up to date on the newest guidelines as they emerge.

For more information on the A1cNow CLIA waived and NGSP certified test for office or home use:  www.a1ctest.com