OTK18 is a C2H2 type zinc finger protein expressed by human macrophages following HIV infection. OTK18 possesses antiretroviral activity, and its processing products accumulate in the cytoplasm of perivascular brain macrophages in advanced HIV encephalitis cases. Since the regulation of OTK18 expression in living patients following human immunodeficiency virus-1 (HIV-1) infection is unknown, our objective is to investigate the first cohort study on OTK18 protein levels in living patients. We assessed OTK18 levels in plasma and cerebrospinal fluid (CSF) in 44 living patients with or without HIV-1 infection, with diverse demographic and clinical background. A novel high-sensitivity OTK18 ELISA system was developed to measure OTK18 levels in CSF and plasma using custom made biotinylated monoclonal antibodies against OTK18. The correlation of OTK18 levels with epidemiological parameters was statistically analyzed. Multiple linear regression modeling suggested that plasma OTK18 levels for HIV-1-positive subjects were only about one sixth of that for HIV-1-negative subjects. Higher CD8 T-cell counts were associated with higher levels of OTK18. Using proportional odds logistic regression, we showed that HIV-1-positive patients have significantly lower OTK18 in CSF samples, but we did not observe significant correlation between CD8 T-cell counts and CSF OTK18 levels. OTK18 levels in both plasma and CSF are significantly lower in HIV-1-positive subjects as compared to HIV-1-negative subjects. Plasma OTK18 levels are positively correlated to CD8 T-cell counts, independent of HIV-1 status.