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

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. 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. 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. 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.