Which of the following investigation is the BEST method of diagnosis of HIV in childhood?

The two tests used for diagnosing HIV infection in in children less than 18 months are detection of HIV nucleic acid (DNA or RNA) AND detection of HIV p24 antigen. Definitive diagnosis requires presence of reactive tests on two separate determinations using one of the above tests after 4 or 6 weeks and confirmed by the second test. Diagnostic testing should be done 6 weeks or longer after complete cessation of breast feeding. Infants born to HIV infected mothers will have HIV antibody until 6-18 months regardless of infection status due to transplacental passage of maternal antibody. The preferred test for infant diagnosis is detection of HIV DNA or RNA in blood, collectively referred to as nucleic acid amplification testing (NAT). Laboratory criteria for diagnosing HIV infection in children more than 18 months: Serologic testing Detection of HIV nucleic acid(DNA or RNA) Detection of HIV p24 antigen Ref: Advances in Pediatrics by Dutta By Jaypee Brothers, page 256. McFarland E.J. (2012). Chapter 41. Human Immunodeficiency Virus Infection. In W.W. Hay, Jr., M.J. Levin, R.R. Deterding, J.J. Ross, J.M. Sondheimer (Eds), CURRENT Diagnosis & Treatment: Pediatrics, 21e.