Anti-Ku Antibodies: Clinical Associations, Organ Damage, and Prognostic Implications in Connective Tissue Diseases.

Anti-Ku antibodies are rare autoantibodies associated with connective tissue diseases (CTDs), but their clinical significance remains poorly understood due to limited studies. Semi-quantitative immunodot assays yield positive, negative, or borderline results, with the clinical relevance of borderline findings remaining unclear. The purpose of this study is to characterize the clinical spectrum of anti-Ku-positive patients and evaluate the clinical significance of anti-Ku-borderline results in CTD management. A retrospective cohort study was conducted at Hôpital Erasme, including all patients with anti-Ku-positive or borderline results, over a 10-year period. Clinical and biological data were collected from medical records and analyzed for disease associations, organ involvement, and outcomes. Among 47 anti-Ku-positive patients, systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) were the most common diagnoses. Interstitial lung disease (ILD) occurred in 23.4% and renal involvement in 12.8% of patients. Cytopenia was significantly associated with glomerulonephritis. Organ damage, particularly pulmonary and renal involvement, correlated with increased mortality. In the borderline group (n = 33), SLE and SS remained the predominant diagnoses. During follow-up, three patients died (all with isolated ILD without associated CTD), one required chronic dialysis, and one underwent lung transplantation. ILD was present in 7/22 (31.8%) borderline patients, and renal involvement in 7/32 (21.9%). This study demonstrates significant associations between anti-Ku antibodies and organ damage, with increased mortality risk. The high prevalence of pulmonary and renal involvement in anti-Ku-borderline patients suggests that these results carry substantial clinical significance and should prompt comprehensive CTD evaluation. These findings support treating borderline anti-Ku results with the same clinical vigilance as positive results, given their similar association with severe organ involvement and adverse outcomes.