Information about Assay Methods for Patients with Hemoglobinopath

The NGSP provides a table on the NGSP website at www.ngsp.org/prog/index2.html describing the effects of frequently encountered Hb variants and derivatives on glycohemoglobin measurement for more than 25 assay methods. The NGSP website also includes a list of references for the information summarized in the table.

According to the NGSP, as of July 2007, 14 percent of laboratories are using assay methods with clinically significant HbAS interference; 13 percent use methods with clinically significant HbAC interference. However, after upcoming changes in reagents expected to be complete by the end of 2008, only about 5 percent of laboratories will be using methods resulting in significant HbAS or HbAC interference.

Alternative Tests

Physicians may wish to consider using other measures of average blood glucose levels, such as the fructosamine test, also called glycated serum protein or glycated albumin, with patients who have hemoglobinopathies where an accurate A1C result cannot be obtained. Serum proteins show average glucose levels over a much shorter period of time than the A1C test, usually about 2 to 3 weeks. Moreover, the fructosamine test is not standardized and the relationship of results of this test to glucose levels or risk for complications has not been established.

Anticipated Changes in A1C Reporting

A plan is under way to change how A1C results are reported. Final details will be determined based on the results of a study in progress. Results may be provided in the following ways:

• with the current name and units—as a percentage


• with the current name and as mmol hemoglobin A1C/mole hemoglobin


• as A1C derived average glucose, also called ADAG, in mg/dL or mmol/L—if study results confirm acceptability of this option

Other Conditions that Can Affect A1C Test Results

A number of other conditions, such as those that reduce the life span of red blood cells, can affect A1C results. Recent acute blood loss or hemolytic anemia can falsely lower A1C results. Intake of large amounts of vitamin C or vitamin E can falsely lower or elevate results. Iron deficiency anemia can falsely elevate results.