In a study done by a team of Japanese researchers the diabetes HGB A1C test is best done in conjunction with a fasting plasma glucose (FPG) test to better predict risk of the development of diabetes. The study tested non-diabetic men and women between the ages of 24 to 82. At the beginning of the test 4,103 had A1C and FPG levels within the normal range, 1,167 had elevated FPG only, 382 had elevated A1C only, and 256 had both forms elevated. The results of diagnosis of individuals with elevated levels 4.7 years later found that 8-9% of patients who had only one test were diagnosed with diabetes compared with 60% with both tests.
HGB A1C Diabetes Diagnosis Accuracy
After the American Diabetes Association began endorsing A1C testing for the screening of diabetes several studies were conducted to examine how accurate the test is. Previously FPG and oral glucose tolerance test (OGTT) were used to screen for diabetes in individuals that were not displaying symptoms. A Finnish study from 2011 found that the A1C test missed some cases of diabetes. Using a group of 522 overweight subjects with impaired glucose tolerance, they found “of those with diabetes diagnoses based on two OGTTs, 60% would have remained undiagnosed if diagnosis had been based on A1C using ADA criteria”.
HGB A1C Diagnosis of Diabetes – Varying Reliability of A1C Test in Different Age Groups and Races
In a 2010 study by Kasia Lipska of Yale University School of Medicine, there was a considerable difference in the cases of diabetes and pre diabetes diagnosed in elderly people using FPG and A1C tests. Another age group that may have a trouble with A1C testing is adolescents. There has been a reported “lack of sensitivity” of the A1C test in a study by Joyce M. Lee. Lee compared A1C, FPG, and OGTT results for a group of 1,156 overweight and obese teens ages 12-18 to test results of 6,751 adults ages 19-70. The results found that A1C did not perform as well amongst the teens as it did with the adults while FPG and OGTT were found to be more sensitive.
Accuracy of the A1C test may also be affected by genetics as well. Different genetics can create variation in the way that sugars bind to hemoglobin and lipids during the life span of red blood cells. Thus, the Endocrine Society began a study of the A1C diagnosis of persons of non-European ancestry as these populations tend to have a higher prevalence of being placed in a pre diabetic category when using A1C testing versus FPG and OGTT.
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