ADA and viral meningitis: Other CSF diagnostic method, such as the Gamma-interferon release assays (IGRAs), requires large CSF volumes (>6 mL) (Luo et al., 2020), while the Adenosine deaminase (ADA) levels in bacterial and viral meningitis complicate ADA testing interpretation in TBM due to unclear diagnostic cut-offs (Pormohammad et al., 2017).