Quest Diagnostics announced the launch of a new test service that helps physicians evaluate a patient's response to drug therapies used to treat infection with the hepatitis B virus (HBV). The first test of its kind available in the United States, the test is significant because it may help physicians tailor more effective treatments for the up to 2.2 million individuals infected with HBV. Currently, the HBsAg qualitative test is used to aid in diagnosis of patients with HBV. However, this new quantitative test service from Quest 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. With this insight, physicians are better positioned to monitor response to antiviral medications, and may enable them to modify or adjust treatment to help minimize the likelihood of progression and reactivation.