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hba1c alone not a reliable
diagnostic Tool in obese
adolescents
new research by Yale University investigators
indicates that a hemoglobin
A1c (HbA1c) level of 6.5% underestimates
the prevalence of prediabetes and diabetes
in obese adolescents (Diabetes Care
2011;34:1306–11). The results suggest that
HbA1c alone is a poor diagnostic tool in
this population, according to the authors.
The researchers investigated the utility
of HbA1c in obese adolescents because
clinical guidelines recently endorsed HbA1c
to diagnose diabetes and identify patients at
risk for developing diabetes did not include
studies involving adolescent populations.
Studies evaluated to make those recommendations
all involved adults, and little is
known about the use of HbA1c in children
and adolescents.
The study involved 1,156 obese adolescents
with a mean age of 13.3 years who
were not taking medications that might affect
glucose metabolism and who were not
already known to have type 2 diabetes. All
subjects had baseline oral glucose tolerance
tests (OGTT) and HbA1c testing, and a
subgroup of 218 subjects had repeated testing
after a mean of 1.68 years.
At baseline, 77% of subjects had normal
glucose tolerance with HbA1c levels
6.5%.
However, 27% of subjects considered to
have normal glucose tolerance based on
HbA1c results were classified as being prediabetic
based on OGTT. Among subjects
diagNostiC
46 CliniCal laboratory news July 2011
p r o f i L e s
p r o f i L e s
placed in the at-risk group by HbA1c results,
53% were considered to have normal
glucose tolerance and 47% prediabetes or
diabetes based on OGTT. Finally, 12.5% of
subjects considered to have diabetes based
on HbA1c results were designated as having
normal glucose tolerance and 24% to
have prediabetes by OGTT.
Based on these findings, the researchers
called for further investigation about the
role of HbA1c levels in diagnosing prediabetes
and diabetes in adolescents and children.
ovarian cancer screening does not
reduce cancer-related mortality
findings from the landmark Prostate,
Lung, Colorectal and Ovarian (PLCO)
Cancer Screening Trial indicate that for
women in a general population, annual
screening with CA-125 biomarker testing
and transvaginal ultrasound compared
with usual care did not reduce ovarian cancer
mortality (JAMA 2011;305:2295–2303).
At the same time, this testing algorithm increased
invasive medical procedures and
associated harms.
The ovarian cancer arm of PLCO involved
78,216 women age 55–74 years at
enrollment, 39,105 of whom underwent
annual screening, and 39,111 of whom
received usual care. Those in the intervention
arm had CA-125 testing for 6 years and
transvaginal ultrasound for 4 years, with a
median follow-up of 12.4 years.
The investigators found 212 and 176
ovarian cancer cases in the intervention
arm and usual care arms, respectively.
There were 118 ovarian cancer-related
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deaths in the intervention arm, compared
with 100 in the usual care group or
3.1/10,000 person-years versus 2.6/10,000
person-years, respectively. The difference
in survival between the intervention and
usual care groups was not statistically significant,
and no stage shift was observed,
meaning that over the course of the study
among intervention arm subjects in comparison
to normal care subjects, there was
not a decline in cases first diagnosed in later
stages of the disease.
In addition, there was an approximate
5% false-positive rate for each screening
round. Although this rate is comparable to
or even lower than false-positive rates for
mammography screening, the researchers
noted that “the nature of the diagnostic
follow-up, which often included invasive
procedures, was a serious concern.” They
concluded that “even an optimized program
of annual screening may be insufficient
to detect cancers early enough to reduce
mortality.”
different centrifugation
conditions Produce similar results
an analysis of centrifugation conditions
on clinical chemistry and immunology
results found that three different conditions
delivered identical test results (BMC
Clinical Pathology 2011 doi:10.1186/1472–
6890-11-6). The results are significant because
they suggest that laboratories may
be able to reduce centrifugation times
and consequently lower their overall turnaround
times.
The researchers conducted the investigation
because although pre-analytical
centrifugation occurs countless times every
day in laboratories around the world,
the influence of the process on lab results
has only rarely and recently been investigated.
World Health Organization (WHO)
guidelines issued in 2002 recommended a
centrifugation time of at least 10 minutes
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for serum and 15 minutes for plasma with
a relative centrifugation force (RCF) of
2,000–3,000g.
The study involved 74 tests on six samples
from 44 consecutively admitted patients,
for a total of 444 results per patient.
The investigators compared three centrifugation
conditions, including 15 minutes at
2,180g RCF, 10 minutes at 2,180g RCF, and
7 minutes at 1,870 g RCF, all at 15°C and
with a deceleration time of 32 seconds. Two
different plasma separators were used for
each centrifugation condition.
The researchers found “identical” results
in all parameters. They conducted Deming
fit, alpha error, and beta error analyses,
and found that only 3.6% of statistical test
results fell outside the p