Validation of the COTS Calculator for Tubercular Uveitis: Predictive Performance and Diagnostic Utility in an Indian Cohort

Diagnosing ocular tuberculosis (OTB) is clinically challenging due to its paucibacillary nature and lack of definitive diagnostic tests. The Collaborative Ocular Tuberculosis Study (COTS) Calculator was developed as a clinical decision-support tool to guide anti-tubercular therapy (ATT) initiation. This study externally validates the COTS Calculator in a high-burden Indian cohort and assesses the additive value of radiological and immunological testing. This retrospective cohort study included 196 OTB patients treated between 2015 and 2022 at a tertiary eye care center in South India. Inclusion required complete diagnostic workup, ≥6-month follow-up post-ATT, and at least one supportive test (TST, IGRA, CT, or CXR). Two thresholds were evaluated: M4I1 (median ≥ 4) and M4I2 (median ≥ 4, IQR ≤ 2). Treatment response and recurrence were primary outcomes. Diagnostic performance was measured using AUC, sensitivity, specificity, PPV, and NPV. Composite scores (CT+CXR and TST+IGRA) were also analyzed. The M4I2 threshold yielded higher sensitivity (83%) than M4I1 (60%) with comparable AUC (0.60 vs 0.58), though at lower specificity (38% vs 56%). Both thresholds achieved high PPV (94%) but poor NPV (11–17%). Composite testing showed similar high PPV (93%) and poor NPV (9–11%). Higher COTS scores and multiple positive tests correlated with favorable treatment response. The COTS Calculator, particularly the M4I2 model, provides a useful clinical tool to guide ATT decisions in OTB. While limited in ruling out TB, its integration with radiological and immunological testing supports early treatment decisions in TB-endemic settings. Prospective validation is warranted.