2606.02772 ANA Patterns in the Gray Zones of Autoimmunity: A Bayesian and Monte Carlo Analysis of Undifferentiated Autoimmune Disease
**Background:** Patients with positive antinuclear antibodies (ANA) who do not fulfill classification criteria for a specific connective tissue disease (CTD) are often labeled as having "undifferentiated" autoimmune disease — a diagnostic category that functions as a clinical waiting room. ANA patterns classified by the International Consensus on ANA Patterns (ICAP) contain prognostic information that remains systematically underutilized.