This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
A patient was presented with sudden onset of fever, headache, retro orbital pain, and back pain along with the severe body pain. Macular rash was present. Clinical diagnosis of dengue fever was made. Which of the following is the most sensitive diagnostic test in this patient? 
Select and explain. 
A. IgM ELISA, B. CFT, C. Tissue culture, D. Electron microscopy
A: IgM ELISA
Answer: A: IgM ELISA 
Explanation: Laboratory findings include leukopenia, thrombocytopenia, and, in many cases, serum aminotransferase elevations. The diagnosis is made by IgM ELISA or paired serology during recovery or by antigen-detection ELISA or -PCR during the acute phase. Virus is readily isolated from blood in the acute phase if mosquito inoculation or mosquito cell culture is used. Ref: Peters C.J. (2012). Chapter 196. Infections Caused by Ahropod- and Rodent-Borne Viruses. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.