Author Affiliations: Clinical Trials Unit, Charles R. Drew University of Medicine and Science (Dr Davidson), Department of Medicine (Drs Davidson and Peters), Emergency Medical Center (Dr Schriger and Mr Lorber), and School of Medicine (Drs Davidson, Schriger, and Peters and Mr Lorber), University of California, Los Angeles.
Context New criteria for the diagnosis of type 2 diabetes
mellitus have recently been introduced that lowered the diagnostic
fasting plasma glucose (FPG) concentration from 7.8 to 7.0 mmol/L (140
to 126 mg/dL).
Objective To determine if individuals with diabetes diagnosed by
the new FPG concentration criterion would have excessive glycosylation
(elevated hemoglobin [HbA1c] levels).
Definitions We determined the distribution of
HbA1c levels in individuals using 4 classifications: (1)
normal by the new criterion (FPG concentration <6.1 mmol/L [110
mg/dL]); (2) impaired fasting glucose by the new criterion (FPG
concentration of 6.1-6.9 mmol/L [110-125 mg/dL]); (3) diabetes
diagnosed solely by the new FPG concentration criterion of 7.0 through
7.7 mmol/L (126-139 mg/dL); and (4) diabetes diagnosed by the previous
FPG concentration criterion of 7.8 mmol/L (140 mg/dL) or higher.
Design Cross-sectional analysis of 2 large data sets (NHANES
III and Meta-Analysis Research Group [MRG] on the Diagnosis of
Diabetes Using Glycated Hemoglobin) that contained individuals in whom
FPG concentrations, 2-hour glucose concentrations using an oral glucose
tolerance test, and an HbA1c level were simultaneously
measured. We cross-tabulated FPG concentrations (<6.1 mmol/L [110
mg/dL], 6.1-6.9 mmol/L [110-125 mg/dL], 7.0-7.7 mmol/L [126-139
mg/dL], and ≥7.8 mmol/L [140 mg/dL]) and HbA1c levels
separated into 3 intervals: normal, less than the upper limit of normal
(ULN); slightly elevated, ULN to ULN plus 1%; and high, higher than
ULN plus 1%.
Results Among subjects with normal FPG concentrations,
HbA1clevels in the NHANES III (and the MRG) data sets were
normal in 97.3% (96.2%), slightly elevated in 2.7% (3.6%), and high
in 0.1% (0.2%). Among individuals with impaired fasting glucose,
HbA1c concentrations were normal in 86.7% (81.4%),
slightly elevated in 13.1% (16.4%), and high in 0.2% (2.2%). Among
diabetic patients diagnosed by the new FPG criterion only,
HbA1c levels were normal in 60.9% (59.6%), slightly
elevated in 35.8% (32.8%), and high in 3.4% (7.6%). In diabetic
patients diagnosed by the former FPG criterion, HbA1c
levels were normal in 18.6% (16.7%), slightly elevated in 32.5%
(21.0%), and high in 48.9% (62.3%).
Conclusions About 60% of the new cohort of diabetic patients in
both data sets have normal HbA1c levels. We believe that
diabetes should not be diagnosed in those with FPG concentrations less
than 7.8 mmol/L (140 mg/dL) unless excessive glycosylation is evident.
Individuals without excessive glycosylation but with moderate
elevations of FPG concentrations (6.1-7.7 mmol/L [110-139 mg/dL])
should be diagnosed as having impaired fasting glucose and treated with
an appropriate diet and exercise. This diagnostic labeling achieves the
goal of early intervention without subjecting these persons to the
potentially negative insurance, employment, social, and psychological
consequences of a diagnosis of diabetes mellitus.
Davidson MB, Schriger DL, Peters AL, Lorber B. Relationship Between Fasting Plasma Glucose and Glycosylated HemoglobinPotential for False-Positive Diagnoses of Type 2 Diabetes Using New Diagnostic Criteria. JAMA. 1999;281(13):1203-1210. doi:10.1001/jama.281.13.1203