Quest Diagnostics has launched a quantitative hepatitis B virus surface antigen (HBsAg) test to help evaluate a patient’s response to drug therapies used to treat infection with the hepatitis B virus (HBV). This is the first test of its kind available in the U.S. Currently, the HBsAg qualitative test is used to aid in the diagnosis of patients with HBV. However, Quest’s new test service measures the quantity, not just the presence, of viral antigen in blood to help determine if the immune system of an individual infected with HBV is responding to treatment. “While there are effective therapies that can functionally cure HBV infection, physicians in the U.S. have lacked tools that help predict individualized patient response to those treatments,” said Rick L. Pesano, MD, PhD, vice president of research and development at Quest Diagnostics. “With this new test capability, physicians can better develop tailored treatment plans and monitor HBV-infected patients to help prevent progression and better their chance for long-term immunity.”