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

Abstract

Purpose: 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.

Methods: 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.

Results: 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.

Conclusions: 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.