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Fast Test for Infant Infections

6 April 1998 7:30 pm
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A new blood test can quickly reveal whether an infant has a bacterial infection. If the test, described in the March Journal of Pediatrics, can be developed for widespread use, it could help doctors save some infants' lives as well as millions of dollars in treatments for babies who seem to have infections.

Because newborns are so vulnerable to infections, doctors have to make snap decisions about whether a baby who looks sick actually needs an antibiotic. Often erring on the safe side, doctors end up treating 17 healthy babies for every one that is later confirmed to have an infection. For a decade, immunologists have searched for a molecule in the newborn immune system that could serve as a warning flag for an infection. But of the molecules tested so far, none has proven reliable.

Leonore Herzenberg, Erica Weirich, and their colleagues at Stanford University Medical Center set out to develop a simple blood test for the latest and most promising sentinel molecule, called CD11b. The molecule appears on the surface of neutrophils, a kind of immune cell, within 5 minutes after being exposed to a bacterial toxin called lipopoly saccharide. The researchers designed a fluorescent marker that clings to CD11b and can be viewed routinely under laserlight. They screened blood from 106 infants suspected to have an infection, or be at high risk for one. They also followed up with a proven, but slower, test for an infection that flags C-reactive protein (CRP). All 15 babies who tested positive for CRP, which is produced in large quantities during an infection, also were positive for CD11b. What's more, there were no false positive CD11b results.

If confirmed, the results "could ultimately change the way that physicians decide how to treat newborn infants," says Herzenberg. But Robert Baltimore, a pediatrician at Yale University Children's Hospital, isn't so sure. Although the test "has a very high predictive value," he says, it could suffer the fate of many previous lab tests for babies--doctors ignore them. "Very often they'll order the test and treat babies anyway," even if the test comes out negative, he says.

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