CONTEXT: Hemoglobin A1c (A1c) was recently added to the diagnostic criteria for 
diabetes and prediabetes.
OBJECTIVE: Our objective was to examine performance of A1c in comparison with 
fasting plasma glucose (FPG) in diagnosing dysglycemia in older adults.
DESIGN AND SETTING: We conducted a cross-sectional analysis of data from the 
Health, Aging, and Body Composition study at yr 4 (2000-2001) when FPG and 
standardized A1c measurements were available.
PARTICIPANTS: Of 3075 persons (aged 70-79 yr, 48% men, 42% Black) at study 
entry, 1865 participants without known diabetes who had appropriate measures 
were included.
MAIN OUTCOME MEASURES: Sensitivity and specificity of A1c-based diagnoses were 
compared with those based on FPG and the proportion of participants identified 
with dysglycemia by each measure.
RESULTS: Of all participants, 2.7 and 3.1% had undiagnosed diabetes by FPG≥126 
mg/dl and A1c≥6.5%, respectively. Among the remaining participants, 21.1% had 
prediabetes by impaired fasting glucose (≥100 mg/dl) and 22.2% by A1c≥5.7%. 
Roughly one third of individuals with diabetes and prediabetes were identified 
by either FPG or A1c alone and by both tests simultaneously. Sensitivities and 
specificities of A1c compared with FPG were 56.9 and 98.4% for diabetes and 47.0 
and 84.5% for prediabetes, respectively. Blacks and women were more likely to be 
identified with dysglycemia by A1c than FPG.
CONCLUSIONS: In this older population, we found considerable discordance between 
FPG- and A1c-based diagnosis of diabetes and prediabetes, with differences 
accentuated by race and gender. Broad implementation of A1c to diagnose 
dysglycemic states may substantially alter the epidemiology of these conditions 
in older Americans.