were not obtained. Thus, data from the
subsamples are considered to represent the
entire NHANES III sample.
The procedures for blood collection and
processing have been described (12).
Venous whole blood was collected into a
vacuum tube containing the glycolytic
inhibitors potassium oxalate and sodium
fluoride and was centrifuged immediately at
1500gfor 10 min. The plasma was frozen at
7 0oC, shipped on dry ice to the University
of Missouri Diabetes Diagnostic Laboratory,
and stored at 7 0oC until analysis. Plasma
glucose was measured using a modified hexokinase
enzymatic method. Both withinassay
and between-assay quality control
procedures were used; the coefficient of variation
of the method was 1.6–3.7% during
the 6 years of the survey (12).
People without previously diagnosed
diabetes were categorized according to
American Diabetes Association diagnostic
criteria as follows: undiagnosed diabetes,
fasting plasma glucose 126 mg/dl;
impaired fasting glucose, fasting plasma glucose
110 to 126 mg/dl. Using 1980–1985
WHO criteria , the diagnostic criteria
for people without diagnosed diabetes were
undiagnosed diabetes, fasting plasma glucose
140 mg/dl or 2-h plasma glucose
200 mg/dl; impaired glucose tolerance,
fasting plasma glucose 140 mg/dl and 2-
h plasma glucose 140 to 200 mg/dl.