Fasting And Post-Challenge Hyperglycemia
Indicates Distinct Pathways in Progression Of
Type 2 Diabetes
Two measurements may represent distinct phenotypic
pathways in the evolution of type 2 diabetes,
new research suggests.
People with abnormal fasting and post-challenge
hyperglycemia appear to have different rates of
progression to diabetes; therefore, these 2 measurements
may represent distinct phenotypic pathways in
the evolution of type 2 diabetes.
Impaired fasting glucose (IFG) refers to a mildly
elevated glucose level immediately after an oral
glucose tolerance test (OGTT), whereas impaired
glucose tolerance (IGT) indicates a mildly elevated
plasma glucose levels 2 hours later. In the United
States, detection of diabetes relies on measurement
of fasting plasma glucose levels alone, and it
is assumed that the value is predictive of impaired
glucose tolerance and ultimately type 2 diabetes.
This assumption has not been validated in longitudinal
studies, however.
James B. Meigs, MD, MPH, with the Massachusetts
General Hospital and Harvard Medical School, Boston,
and colleagues studied this progression using
biennial oral glucose tolerance tests and survival
analysis to assess progression from normal glucose
tolerance (NGT) to abnormal fasting plasma glucose
(FPG; >110mg/dL or 6.1 mmol/L); abnormal 2-h
plasma glucose (2hPG; >140mg/dL or7.8 mmol/L);
impaired fasting glucose (IFG) (FPG 110mg/dL or
6.1-6.9 mmol/L, 2hPG <140mg/dL.or7.8 mmol/L);
and IGT (FPG <110mg/dL. Or 6.1 mmol/L, 2hPG
140mg/dL or7.8-11.0 mmol/L). It was also used
to assess progression from IFG-IGT to diabetes
(FPG >126mg/dL or7.0 mmol/L or 2hPG >200mg/dL
or 11.1 mmol/L).
At baseline, 815 subjects of the Baltimore Longitudinal
Study of Aging had a mean age of 57 years, 35%
were women, and 60% (n=488) had NGT. Of those,
over half were followed for at least 10 years.
By 10 years, 14% had progressed to abnormal FPG,
and 48% had progressed to abnormal 2hPG, the researchers
report. Of the 267 subjects who progressed to
IFG-IGT, 216 were followed for an additional 10
years. During that time, 8% of them progressed
to diabetes by FPG whereas 27% progressed by 2hPG.
However, of the subjects developing abnormal FPG,
42% did not develop abnormal 2hPG, and vice versa.
"These data suggest that abnormal FPG and
2hPG levels are not necessarily part of a continuum
in the evolution of hyperglycemia," the researchers
conclude.
Dr. Meigs and colleagues note that detection
programs "relying solely on elevated FPG
levels using current diagnostic thresholds may
only detect the more uncommon IFG phenotype, and
miss a substantial number of subjects at risk
for diabetes on the basis of abnormal 2hPG levels."
They also point out that specifying a lower "abnormal"
FPG level (in the 100mg/dL-103mg/dL or 5.55-5.7
mmol/l range), using the OGTT, or identifying
clusters of insulin resistance-related traits
may be required to maximize identification of
subjects at risk for developing type 2 diabetes.
Diabetes. 2003 Jun;52(6):1475-1484
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FACT:
Intensified blood glucose monitoring improved
glycemic control in a large cohort of stable,
insulin-treated veterans with type 2 diabetes.
SMBG provided a strong stimulus for improved self-care
resulting in clinically important and sustained
reductions in HbA1c. Diabetes Care 26:1759-1763,
2003
