Hemoglobin variants can interfere withthe measurement of A1C, although mostassays in use in the U.S. are unaffected bythe most common variants. Marked discrepanciesbetween measured A1C andplasma glucose levels should prompt considerationthat the A1C assay may not bereliable for that individual. For patientswith a hemoglobin variant but normalred blood cell turnover, such as thosewith the sickle cell trait, an A1C assaywithoutinterference from hemoglobin variantsshould be used. An updated list of A1Cassays with interferences is available atwww.ngsp.org/interf.asp.