HIV infection is commonly diagnosed by detection of antibodies (anti-HIV) by ELISA or agglutination. Reactive results are confirmed by western blot (immunoblot) or further specific tests such as competitive ELISA, which, when evaluated quantitatively, allow the differentiation of HIV types and partially subtypes. Detection of infection of newborn babies, characterisation of individual strains for subtyping and forensic identification, and therapeutic monitoring are the domain of nucleic-acid-based assays. Nucleic-acid-based assays narrow the serological diagnostic window period in early HIV infection and, when quantified, give some indication of clinical status.