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Heel-stick procedure in new-borns said
not effective in screening for cytomegalovirus (CMV) infection
A routine screening test for several metabolic and genetic disorders in
newborns, the heel-stick procedure, is not effective in screening for
cytomegalovirus (CMV) infection, a leading cause of hearing loss in
children, according to research published in the April 14 online issue of
the Journal of the American Medical Association.
About 20,000-30,000 infants are born infected with CMV each year, 10-15
percent of whom are at risk for eventually developing hearing loss.
The study, funded by the National Institute on Deafness and Other
Communication Disorders (NIDCD), one of the National Institutes of Health,
is part of a multicenter research project headed by the University of
Alabama at Birmingham that is seeking to find the most effective screening
test for CMV infection in newborns.
The standard method for detecting CMV
infection in newborns is labor-intensive and not conducive to a widespread
screening program.
The heel-stick test is a simple test that is already being used to screen
for other diseases in newborns across the United States, so it seemed like a
good candidate for a possible universal screening program for CMV, said
James F. Battey, Jr., M.D., Ph.D., director of the NIDCD.
However, these
findings show us that, at least with current technologies, the heel-stick
test should not be used as a primary newborn screening tool for CMV.
CMV is the most common infection passed from a mother to her unborn child.
The vast majority of CMV-infected babies show no initial symptoms, and many
babies will never develop health problems. But in some CMV-infected babies,
serious problems can develop over time.
Hearing loss is the most common
deficit to emerge later on. The earlier doctors can identify CMV infection,
the better they can monitor a child~Rs hearing. If signs of hearing loss are
present, appropriate intervention should be provided as soon as possible.
Between March 2007 and May 2008, the researchers analyzed dried blood
samples obtained using the heel-stick procedure from babies born at the
University of Alabama at Birmingham, and six other participating medical
centers across the United States.
The heel-stick procedure involves pricking
a newborn's heel, drawing a small amount of blood, and placing the blood on
filter paper to dry so that it can be analyzed for several diseases,
including hypothyroidism and sickle cell disease.
To test for CMV infection, the researchers removed the babies' DNA from the
filter paper and then used a common molecular diagnostic technique to
quickly and efficiently detect whether any CMV DNA was mixed in.
The
procedure, called real-time polymerase chain reaction, or PCR, uses special
molecules, called primers, to seek out a tell-tale portion of CMV DNA and
churn out lots of fluorescent copies of that segment so it can be easily
detected.
For the initial group of babies, the researchers used a single set
of primers targeting one section of CMV DNA. As the study progressed, they
added a second primer set targeting an additional section in hopes of
increasing accuracy, or sensitivity, of the test.
The team also compared their results to the standard method of detecting CMV
in newborns. CMV rapid culture is a highly effective procedure that uses
saliva or urine instead of dried blood samples to make the identification.
The rapid culture method is labor-intensive and requires a tissue culture
facility on site, so it would be difficult to adapt this technology to a
widespread screening program.
Many studies have found that dried blood spot PCR is able to identify babies
with congenital CMV infection, so some researchers have suggested that it be
used for a universal screening program.
However, none of the earlier studies
compared dried blood spot PCR results to the rapid culture method and
therefore could not determine if the PCR procedure was as good as the
standard or if it fell short and missed truly infected babies or falsely
identified babies as being CMV-infected when they were not infected.
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