Utility of CBC-derived ratios in the diagnosis and prediction of active tuberculosis in people with rheumatic diseases

OBJECTIVE: Active tuberculosis (ATB) largely relied on clinical diagnosis because of the limited sensitivity of microbiologic testing. We assessed whether complete blood cell count (CBC)-derived ratios could assist in ATB diagnosis and risk assessment. METHODS: This study enrolled 305 people with ATB and 171 healthy controls (HC) to evaluate the diagnostic efficiency of CBC-derived ratios for ATB by receiver operating characteristic curves and validated in a multi-center rheumatic disease (RD) cohort, in which a nested case-control study was designed to reveal the relationship between CBC-derived ratios and risk of developing ATB. RESULTS: Platelet, monocyte, and neutrophil count increased, but lymphocyte count decreased, thereby, platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), and neutrophil-to-lymphocyte ratio (NLR) were elevated significantly in people with ATB compared to HC, the similar tendency was shown between people with post- and pre-the onset ATB. These indices were restored after anti-tuberculosis treatment. Moreover, PLR, MLR, NLR, especially combining monocyte count, PLR, and NLR (area under the curve (AUC) = 0.916, P < 0.001) exhibited good diagnostic efficiency for ATB. Additionally, people with RD concomitant ATB demonstrated a similar tendency of CBC-derived ratios but their diagnostic efficiency for ATB was limited in the RD population. Interestingly, the risk of developing ATB of people with PLR ≥ 130.27 was higher by 23.761-fold than those with PLR < 130.27 in this population within one year. CONCLUSION: CBC-derived ratios have limited standalone diagnostic value in RD populations (AUC = 0.637) but may aid risk stratification. CBC-derived ratios should be considered complementary tools, not replacements, for microbiological tests, particularly in resource-limited settings or to prompt further definitive testing.