Limited Agreement between Classifications of Diabetes and Prediabetes Resulting from the OGTT, Hemoglobin A1c, and Fasting Glucose Tests in 7412 U.S. Adults.
Level 4 - case-series / case-control
Cross-sectional diagnostic concordance study using survey data.
PubMed 32668564 · doi:10.3390/jcm9072207
What was done
Researchers analyzed data from 7,412 randomly selected adults in the National Health and Nutrition Examination Survey (NHANES) to assess diagnostic agreement between fasting plasma glucose (FPG), hemoglobin A1c (A1c), and the oral glucose tolerance test (OGTT). Participants were classified into normal, prediabetes, or diabetes categories according to standard guidelines. Concordance was also assessed across sex and three age groups, as well as for the combined use of FPG and A1c against OGTT.
What was found
Agreement across tests was low. In individuals diagnosed with diabetes by OGTT, concordance was 34% for A1c and 44% for FPG. Among older adults, concordance with OGTT dropped to 25% for A1c and 33.5% for FPG. Combining FPG and A1c aided the identification of diabetes and normal glycemia, but did not resolve discordance for prediabetes.
Why it matters
Standalone FPG or A1c measurements miss a substantial proportion of diabetes cases detected by OGTT, particularly in older populations. Relying on single routine markers risks significant misclassification without confirmatory or combined testing.
Limits
The abstract does not report specific numerical concordance values for prediabetes, normal glycemia, or sex-stratified subgroups. As a cross-sectional survey analysis, it cannot determine whether OGTT-positive but A1c/FPG-negative individuals had differing long-term clinical outcomes.
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