Evaluation of prognostic inflammatory and systemic inflammatory response indices in auxiliary diagnosis of bacteria-negative pulmonary tuberculosis: A diagnostic accuracy study

**Background:** Tuberculosis remains a global health challenge, with bacteria-negative pulmonary TB accounting for approximately 55% of cases in China. Diagnosis of bacteria-negative TB is difficult due to nonspecific clinical manifestations, leading to delayed treatment and increased morbidity and mortality. The prognostic inflammatory index (PII) and systemic inflammatory response index (SIRI) are novel composite biomarkers reflecting inflammation, nutrition, and immune status, but their utility in TB diagnosis had not been previously studied.

**Methods:** This retrospective diagnostic accuracy study included 60 patients with bacteria-negative pulmonary TB (case group) and 70 patients with nontuberculous pulmonary infection (control group) from the Affiliated Hospital of Qinghai University, enrolled between October 2019 and September 2022. Baseline demographics, body mass index (BMI), and laboratory parameters including erythrocyte sedimentation rate (ESR), lymphocyte count (LY), neutrophil count (NE), monocyte count (MO), albumin (ALB), prealbumin (PA), C-reactive protein (CRP), and fibrinogen (FIB) were collected. NLR, PII (CRP × NLR/ALB), and SIRI (NLR × MO) were calculated. Receiver operating characteristic (ROC) curves were constructed, and pairwise comparisons of AUCs were performed using SPSS 27.0 and MedCalc 20.1.

**Key Results:** No significant differences were found between groups for sex or age. The case group had significantly lower BMI (21.56 ± 3.66 vs 23.05 ± 3.75 kg/m², P = .03), LY (1.23 ± 0.37 vs 1.84 ± 0.62 × 10⁹/L, P < .001), ALB (38.87 ± 3.92 vs 42.82 ± 3.70 g/L, P < .001), and PA (210.56 ± 61.74 vs 274.81 ± 76.20 mg/L, P < .001). The case group had significantly higher NE (4.12 vs 3.58 × 10⁹/L, P = .03), MO (0.48 vs 0.40 × 10⁹/L, P = .001), CRP (8.50 vs 0.90 mg/L, P < .001), FIB (3.61 vs 2.64 g/L, P < .001), ESR (16.5 vs 5.5 mm/h, P < .001), NLR (3.23 vs 2.02, P < .001), PII (0.60 vs 0.04, P < .001), and SIRI (1.64 vs 0.81, P < .001). ROC analysis showed PII had the highest AUC of 0.84 (95% CI: 0.77–0.90) and highest specificity of 82.86% (95% CI: 72.0–90.8) at a cutoff of 0.20. NLR + PII had the highest sensitivity of 86.67% (95% CI: 75.4–94.1). Pairwise comparison of ROC curves revealed that only the difference between NLR and NLR + PII was statistically significant (Z = 2.36, P = .02).

**Clinical Implications:** PII and SIRI are simple, inexpensive biomarkers derived from routine laboratory tests that demonstrate clinical value in differentiating bacteria-negative pulmonary TB from nontuberculous pulmonary infection. PII showed the highest diagnostic value and specificity, while NLR + PII offered the highest sensitivity. These indices could serve as useful adjuncts in the diagnostic workup, potentially reducing diagnostic delays and improving patient outcomes. However, the study is limited by its retrospective, single-center design with a small sample size, and the findings require validation in larger, multicenter prospective studies.