HBsAg positive blood donors are rejected. Hepatitis B surface antigen is the earliest indicator of the presence of acute infection. Also indicative of chronic infection. Test is useful in the differential diagnosis of hepatitis. Note: Confirmation of a positive result by a neutralization assay at no additional charge This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample. Limitations: Patients who are negative for HBsAg may still have acute type B viral hepatitis. There is sometimes a "core window" stage when HBsAg has become negative and the patient has not yet developed the antibody (anti-HBs). On such occasions, both tests for anti-HBc are usually positive and anti-HBc, IgM is the only specific marker for the diagnosis of acute infection with hepatitis B. In cases with strong clinical suspicion of viral hepatitis, serologic testing should not be limited to detecting HBsAg, but should include a battery of tests to evaluate different stages of acute and convalescent hepatitis.