WASHINGTON - The Food and Drug Administration on Wednesday for the first time approved a type of diagnostic test that will allow doctors to determine what kind of hepatitis C virus a chronically infected patient has, and tailor treatments based on that genetic type.

No vaccine exists for the hepatitis C virus, or HCV, the most common blood-borne infection in the country. HCV infects about 3.2 million people in the U.S and leads to the death of 15,000 people annually.

"Hepatitis C is known as the silent killer, as many of the symptoms go unnoticed," HIV and viral hepatitis expert Carol Brosgart, professor of medicine at UC San Francisco, said in a statement.

Using a patient’s blood plasma or serum, the test -- called the Abbott RealTime HCV Genotype II -- identifies the virus as one of several genotypes, 1, 1a, 1b, 2, 3, 4 and 5. As each responds differently to drug therapies, knowing the type of HCV can help health professionals better determine how it will respond to therapy, improving patient care.

"The genotypes most common in U.S. are 1a and 1b, [which] do not respond particularly well to therapies based upon interferons," University of Tennessee Health Science Center professor Tony Marion said. "Those are most aggressive and harder to treat."

Ten years after the complete sequencing of the human genome, the approval demonstrates the growing use of individual molecular analysis to diagnose and treat diseases, said Edward Abrahams, president for the Personalized Medicine Coalition.

"It’s where medicine is headed," he said.

In addition to avoiding the side effects of ill-fitted drug therapies, linking treatment with genotyping tests can "reduce costs, as we won’t have to prescribe one-size-fits-all treatment to all-comers," he added.

HCV is the leading cause of liver transplants, according to the Centers for Disease Control and Prevention. More than 75% of adults with HCV are baby boomers, most of whom do not know they are infected. Untreated chronic infections may lead to liver cancer, severe liver damage and liver failure.

[For the record: June 25, 1:25 p.m.: An earlier version of this post misspelled the Abbott RealTime HCV Genotype II as Abott.]

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