Clinical Utility of Monocyte-to-Lymphocyte Ratio and Prognostic Nutritional Index in Diagnosing Smear-Negative Pulmonary Tuberculosis with Negative IGRA Results

Objective To evaluate the diagnostic usefulness of the monocyte-to-lymphocyte ratio (MLR) and the prognostic nutritional index (PNI) in smear-negative pulmonary tuberculosis (SN-PTB) patients with a negative interferon-γ release assay (IGRA) result. Methods Between January 2021 to December 2024, 548 consecutive patients suspected of having SN-PTB were enrolled at the Second People's Hospital of Fuyang. After exclusion, 276 patients with SN-PTB (SN-PTB group) and 272 with non-tuberculous (Non-TB) pulmonary infection (Non-TB group) were retrospectively analyzed. Laboratory parameters-including albumin (ALB), pre-albumin (PALB), C-reactive protein (CRP), fibrinogen (FIB), IGRA result, T-cell subsets (CD3 + , CD4 + , CD8 + ), CD4 + /CD8 + ratio, MLR, and neutrophil-to-lymphocyte ratio (NLR)-were compared between groups. Patients were further stratified by IGRA status (positive vs negative). Receiver-operating characteristic (ROC) curves were constructed to assess the diagnostic performance of individual and combined indices. Results In the IGRA-negative subgroup (SN-PTB group: n = 25; Non-TB group: n = 184), MLR was significantly higher in the SN-PTB group ( p = 0.008) and PNI was significantly lower ( p Conclusion MLR, PNI and their combination offer moderate diagnostic value for SN-PTB when the IGRA result is negative; the combined MLR+PNI index performs better than either marker alone. However, these findings should be interpreted with caution due to the limited sample size in the IGRA-negative subgroup, and further validation in larger cohorts is warranted.