Postnatal Fasting Plasma Glucose
Determines Need for Oral Glucose Tolerance Test
British researchers report, that in women
with gestational diabetes, a postnatal oral glucose
tolerance test (OGTT) may only be necessary in
women whose postnatal fasting plasma glucose is
6.0 mmol/L or more.
This finding could spare the need for an OGTT
in more than 90% of women with gestational diabetes,
they add.
Women with gestational diabetes (GDM) are advised
to undergo a postnatal OGTT 6 weeks after delivery.
But compared to the fasting plasma glucose test,
the OGTT is time-consuming, unpleasant, and relatively
expensive.
"Furthermore, as the prevalence of postnatal
diabetes is low in our population (2.4%), we questioned
the value of performing postnatal OGTTs on all
women with a history of GDM," note Richard
I. G. Holt, MD, with the Foetal Origins of Adult
Disease Division and Health Care Research Unit,
University of Southampton, in Southampton, United
Kingdom, and colleagues.
Dr. Holt and colleagues attempted to identify
whether fasting plasma glucose 6 weeks after delivery
could identify which women should also undergo
a postnatal OGTT.
They evaluated 152 women who were diagnosed with
GDM according to World Health Organization criteria
and were advised to have an OGTT 6 weeks postpartum.
They then assessed the results of the fasting
plasma glucose concentration in relation to the
2-hour glucose value from the OGTT.
Of the participants, 19.7% chose not to undergo
an OGTT. Among the remainder, three women had
diabetes, three had impaired glucose tolerance,
and four had impaired fasting glycaemia.
None of the women with a normal OGTT level had
fasting glucose of 6.0 mmol/L or more, and the
two tests were well correlated (r=0.62, P<0.0001).
According to the researchers, only 8.1% of the
OGTTs would have been performed if only women
with fasting glucose of 6.0 mmol/L or greater
underwent the test.
"The sensitivity and specificity of this
approach for the diagnosis of postnatal diabetes
is 100% and 94%, respectively," they report,
and they estimate that selecting women in this
way would miss fewer than three in 10,000 cases.
Dr. Holt and colleagues point out that while
the two tests are well correlated, some groups
of individuals are more likely to be identified
by plasma fasting glucose levels than others.
"Those who are more likely to be identified
by the (OGTT) include the elderly and certain
non-Caucasian ethnic groups. On the other hand,
middle-aged more obese patients are more likely
to have diagnostic fasting values," they
note. Diabet Med 2003;20:7:594-598.
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