CD38 and tuberculosis: In contrast, we observed a rather poor goodness of fit yet, a significant deviation from a non-zero slope between MBLA or Xpert Ct values and the decline of CD38 positive antigen-specific CD4+ T cells that translate into increasing CD38-based TAM-TB results when expressed as a ratio with CD38 negative antigen-specific CD4 T cells (Figures 2B,D).