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Diabetes doctors debate the best diagnostic tests

Controlling blood sugar is also discussed at their convention.

June 15, 2009|Thomas H. Maugh II

Diabetes rates have climbed steeply in this country in the last two decades. Fortunately, scientists' knowledge of how best to manage the disease is advancing as well. Researchers gathered at the American Diabetes Assn. meeting last week in New Orleans to consider the latest developments, including a new test for diagnosing the disease and a better understanding of the risks of aggressive control of blood sugar.

The current techniques for diagnosing Type 2 diabetes involve either a fasting plasma glucose test or, less commonly, an oral glucose tolerance test. In the former, the patient must fast for 12 to 14 hours before the physician measures the level of glucose in his or her blood. In the latter, the patient drinks a solution of concentrated sugar, and blood sugar levels are measured two hours later.

The first test can be affected by eating during the fast, and both can be affected by illness.

Many doctors now believe that a blood analysis for glycated hemoglobin, also known as hemoglobin A1c, is a better test. A1c is a measure of the patient's blood sugar levels for the two to three months preceding the test. The test requires only a sample of blood.

But diabetes groups have been reluctant to recommend wider use of it for diagnosis because only recently have most labs begun using a standardized test for A1c.

A 21-member committee including scientists from the American Diabetes Assn., the International Diabetes Federation and the European Assn. for the Study of Diabetes has been studying literature on the test for several months and, at the meeting, recommended that it be adopted as the primary diagnostic test.

"This is the first major departure from the way diabetes has been diagnosed in the past 30 years," Dr. David Nathan of Harvard Medical School, chairman of the committee, told a news conference.

The committee also concluded that the A1c test is a more accurate predictor of a diabetic's likelihood of developing complications of the disease. Healthy people have an A1c level of 6% or lower; diabetics typically have a level well above 7%. The committee recommended that a cutoff level of 6.5% be used for a diagnosis.

Assessing risks

A1c levels have also been a crucial end point in two large trials studying aggressive control of diabetes.

Doctors already knew that tight control of blood sugar levels is an effective method of preventing cardiovascular and other complications of Type 1 diabetes. But the situation is more complicated for Type 2, which affects the vast majority of the 24 million diabetics in the United States.

Researchers and clinicians had always believed that aggressively lowering sugar levels is beneficial, until two major studies released last year muddied the waters.

One of the trials, called Action to Control Cardiovascular Risk in Diabetes or ACCORD, suggested that aggressively lowering blood sugar caused a 20% increase in deaths, possibly from increased episodes of hypoglycemia, or subnormal blood sugar levels.

The second trial, the Veterans Affairs Diabetes Trial or VADT, found no increased risk of deaths, but no overall benefit from aggressive treatment.

New analyses of the data presented last week provide some insight into the differing findings but fail to answer the question of why some researchers saw increased risks while others didn't.

Two important conclusions they did reach, however, were that diabetics should avoid hypoglycemic episodes no matter what regimen is followed, and that aggressive treatment should begin as soon as possible after diagnosis.

The ACCORD trial enrolled 10,251 diabetics at 77 U.S. and Canadian clinics. Half received treatment to reduce A1c to between 7% and 7.9%, and half received aggressive treatment to try to reduce it to 6%.

Contrary to their initial speculation, the research team has now concluded that the excess deaths in the aggressive treatment arm were not caused by episodes of hypoglycemia, Dr. Matthew Riddle of the Oregon Health Science University in Portland told the meeting. Though severe hypoglycemia was associated with deaths, the risks were the same in both treatment groups.

The team did find a 20% increased risk of death for every 1% rise in A1c above 6%, Riddle said, "suggesting that lower blood glucose levels may be a worthy target." They also found that patients who were more easily able to reduce their A1c levels below 7% had a lower risk of death than those who struggled to do so.

And what caused the increased risk of death in the aggressive treatment group? "We don't know," Riddle said.

The VADT trial enrolled 1,791 patients from 20 VA medical centers, and had the same goals as ACCORD.

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