IDO in respiratory distress patients

Data linked to the proposed publication: Diagnostic accuracy of Kynurenine to tryptophan ratio in peripheral blood to distinguish Tuberculosis from COVID-19, PCP or CAP.

Tuberculosis (TB) kills almost as many people annually as COVID-19 killed in 2020, yet remains challenging to diagnose. The kynurenine (kyn)/tryptophan (trp) ratio, an indicator of indoleamine 2,3-dioxygenase activity, is of interest as a host biomarker of respiratory distress. We calculated the diagnostic potential of the kyn/trp ratio to distinguish TB from COVID-19, community-acquired pneumonia (CAP), Pneumocystis pneumonia (PCP) and non-communicable lung disease. We measured the kyn/trp ratio by ELISA on peripheral blood along with C-reactive protein (CRP) values as a comparator assay of the host immune response. An elevated kyn/trp ratio was seen in individuals with TB, COVID-19, CAP and PCP but not in those with non-communicable diseases. Individuals with TB had the highest kyn/trp ratio. At a cut-off value of 0.165, the kyn/trp ratio was able to differentiate individuals with TB disease from healthy control subjects with a sensitivity of 72.5%, specificity of 100.0%, positive predictive value (PPV) of 100.0% and negative predictive value (NPV) of 93.9%, and from patients with other aetiologies of respiratory distress with a sensitivity of 72.5%, specificity of 74.8%, PPV of 40.5% and NPV of 92.0%. The kyn/trp ratio performed better than CRP for distinguishing TB disease from other respiratory illnesses with the area under the receiver operating curve of 0.76 compared with 0.61. The kyn/trp ratio can be used as an adjunctive blood-based diagnostic test for TB.