<prompt> A person has unprotected sex 3 weeks back, To rule out HIV infection the best test isP 24 antigen assayELISAWestern blotLymphnode biopsy  <response>: Laboratory diagnosis of HIV infectionLaboratory diagnosis is made by:A. Antibody detectionIt is the most common method used for diagnosis of HIV infection.ELISA is the most sensitive test and therefore is the screening test of choice.Western blot is the most specific Confirmatory test and therefore is thegold standard for diagnosis.Antibodies test usually nucleic acid or antigen.B. Detection of HIV nucleic acid or antigenP24 antigen detection by ELISA can be done 16 days after infection earlier than antibody detection.Nucleic acid detection tests are the earliest to become positive 12 days after infection, Most commonly used test is reverse transcriptase PCR, RT-PCR, other methods used are DNA-PCR, RNA-PCR, RNA-bDNA branched DNA, and RNA-NASBA nuclei acid sequenced based assay.C. Virus isolationCo-cultivation of the patients lymphocyte with uninfected lymphocytes in the presence of IL-2.Not suitable as a routine diagnostic procedure.In infected individual HIV can be isolated fromBloodSemenSalivaUrineLymphocytesCervical secretionsTearsBreast milk 