<prompt> A patient presented with fever, cervical lymphadenopathy and night sweats four weeks after unprotected sexual contact. Next investigationp24ELISACD4HIV PCR  <response>: Ref: PubMed This is a possible suspicion of HIV infection. p24 antigen is a viral protein that makes up most of the viral core. Serum concentrations of p24 antigen are high in the first few weeks after infection; tests sensitive to p24 antigen are therefore useful for diagnosing very early infection when antibody levels are still low. 