Impact of mismatches in HbA1c vs glucose values on the diagnostic classification of diabetes and prediabetes. Issue 4 (15th December 2019)

• Record Type: Journal Article
• Authors: Gonzalez, A.; Deng, Y.; Lane, A. N.; Benkeser, D.; Cui, X.; Staimez, L. R.; Ford, C. N.; Khan, F. N.; Markley Webster, S. C.; Leong, A.; Wilson, P. W. F.; Phillips, L. S.; Rhee, M. K.
• Is Part Of: Diabetic medicine. Volume 37:Issue 4(2020)
• Page Start: 689
• Page End: 696
• Publication Date: 2019-12-15
• Subjects: Diabetes -- Periodicals; 616.462
• DOI: 10.1111/dme.14181
• Languages: English
• ISSNs: 0742-3071

Abstract

Abstract: Aims: To determine whether HbA1c mismatches (HbA1c levels that are higher or lower than expected for the average glucose levels in different individuals) could lead to errors if diagnostic classification is based only on HbA1c levels. Methods: In a cross‐sectional study, 3106 participants without known diabetes underwent a 75‐g oral glucose tolerance test (fasting glucose and 2‐h glucose) and a 50‐g glucose challenge test (1‐h glucose) on separate days. They were classified by oral glucose tolerance test results as having: normal glucose metabolism; prediabetes; or diabetes. Predicted HbA1c was determined from the linear regression modelling the relationship between observed HbA1c and average glucose (mean of fasting glucose and 2‐h glucose from the oral glucose tolerance test, and 1‐h glucose from the glucose challenge test) within oral glucose tolerance test groups. The haemoglobin glycation index was calculated as [observed – predicted HbA1c ], and divided into low, intermediate and high haemoglobin glycation index mismatch tertiles. Results: Those participants with higher mismatches were more likely to be black, to be men, to be older, and to have higher BMI (all P <0.001). Using oral glucose tolerance test criteria, the distribution of normal glucose metabolism, prediabetes and diabetes was similar across mismatch tertiles; however, using HbA1c criteria, the participants with low mismatches were classified as 97% normal glucose metabolism, 3% prediabetes and 0% diabetes, i.e. mostly normal, while those with high mismatches were classified as 13% normal glucose metabolism, 77% prediabetes and 10% diabetes, i.e. mostly abnormal ( P <0.001). Conclusions: Measuring only HbA1c could lead to under‐diagnosis in people with low mismatches and over‐diagnosis in those with high mismatches. Additional oral glucose tolerance tests and/or fasting glucose testing to complement HbA1c in diagnostic classification should be performed in most individuals. What's new?: HbA1c mismatches, that is, HbA1c levels that are higher or lower than expected for average glucose levels, can limit the accuracy of HbA1c measurements in diabetes diagnosis and management, but their potential impact is not widely appreciated. In a diabetes screening cohort using the 75‐g oral glucose tolerance test (OGTT) as the 'gold standard', use of the HbA1c test alone led to under‐diagnosis in participants with low HbA1c mismatches and over‐diagnosis with high HbA1c mismatches. Because HbA1c mismatches could lead to errors, diagnoses of diabetes/prediabetes should include measurement of glucose levels (fasting, OGTT) in addition to HbA1c in most individuals.