This document updates recommendations for HIV testing by laboratories in the United States and offers approaches for reporting test results to persons ordering HIV tests and to public health authorities. The recommended algorithm is a sequence of tests used in combination to improve the accuracy of the laboratory diagnosis of HIV based on testing of serum or plasma specimens. The updated recommendations also include tests for HIV antigens and HIV nucleic acid because studies from populations at high risk for HIV demonstrate that antibody testing alone might miss a considerable percentage of HIV infections detectable by virologic tests