This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infection, Subject name: Pediatrics
All of the following are used in diagnosis of HIV in a 2 month old child except: 
Select and explain. 
A. HIV ELISA, B. p24 antigen assay, C. DNA PCR, D. Viral culture
A: HIV ELISA
Answer: A: HIV ELISA 
Explanation: Ans. A. HIV ELISAHIV ELISA cannot be used in diagnosis of HIV in a child up to 18 months of age.* This is because all neonates born to HIV infected mothers will have IgG antibody in their blood regardless of their infection status.* So up until 18 months of age they will continue to test positive. Hence HIV ELISA should not be used.