Researchers have determined in a new study that a low BMI (<25 kg/square meter) increases the risk of progression to active TB among individuals who are IGRA positive and not on TPT by a significant margin. The study proved that BMI is an easy and measurable biomarker that can be utilized to identify high-risk groups so that targeted prevention can be implemented. The study was conducted by Maria B. and colleagues published inmedRxiv. The study was carried out in the setting of the RePORT-Brazil prospective multi-center cohort between 2015 and 2019, recruiting 1846 contacts of 619 pulmonary TB cases. The participants were followed up for 24 months to evaluate risk factors for progression to TB. Researchers used empirical review and LASSO regression on baseline laboratory and clinical data to identify variables to include in predictive models. Three predictive models were developed: 1) all contacts, 2) IGRA-positive contacts at baseline, and 3) IGRA-positive contacts who were not treated with TPT (<30 days of isoniazid). Internal validation was conducted with bootstrapping and performance was quantified using the area under the receiver operating characteristic (ROC) curve. • At follow-up, 25 of 1846 contacts (1.4%) developed TB. Inadequate TPT was a strong predictor of progression in all contacts, with mixed-effects adjusted hazard ratio (aHR): 11.79 (95% CI: 1.55–89.77). • The model using all contacts showed excellent discrimination with AUC = 0.85 (95% CI: 0.78–0.91). • For TPT-naive IGRA-positive contacts, BMI was the key determinant of TB development. BMI had a reverse association with risk (aHR: 0.87, 95% CI: 0.78–0.98). • Within this subgroup, individuals with BMI <25 kg/m² were at 4.14 times (95% CI: 1.17–14.67) higher risk of developing TB compared with those with BMI ≥25 kg/m². •The absolute TB risk was 8.4% for BMI <25 and 2.1% for BMI ≥25. This research concluded that BMI <25 kg/m² is a robust predictor of TB progression in IGRA-positive contacts who are not on preventive therapy. With the application of BMI as a biomarker, clinicians are able to identify those at high risk and target TPT for those most in need. These results offer pragmatic recommendations for enhancing TB prevention programs and lowering the global burden of active TB disease. Arriaga, M. B., Amorim, G., Figueiredo, M. C., Staats, C., Kritski, A. L., Cordeiro-Santo, M., Rolla, V. C., Rebeiro, P. F., Andrade, B. B., Sterling, T. R., & RePORT-Brazil consortium (2025). Body Mass Index and Incident Tuberculosis in Close Tuberculosis Contacts. medRxiv : the preprint server for health sciences, 2025.04.15.25325878. https://doi.org/10.1101/2025.04.15.25325878