Clinical Utility of Anti-nuclear Antibodies and Extractable Nuclear Antigen for Diagnosis of Connective Tissue Disorders

Connective tissue disorders (CTDs) are associated with the production of multiple autoantibodies, predominantly anti-nuclear antibodies (ANA) and their subsets known as extractable nuclear antigens (ENA). Although ANA detection by indirect immunofluorescence (IIF) and enzyme-linked immunosorbent assay (ELISA) is routinely used for screening CTDs, these methods are limited by non-specificity. The present study evaluated the clinical utility of ENA profiling in conjunction with conventional ANA testing for CTD screening. Clinically suspected CTD patients were screened for ANA using ELISA and IIF, followed by ENA antibody detection using ELISA and line blot immunoassay (LIA). Out of a total of 274 clinically suspected cases analyzed, ANA positivity was observed in 23.7% of cases by indirect immunofluorescence and 26.2% by enzyme-linked immunosorbent assay. ENA analysis among ANA-positive cases revealed systemic lupus erythematosus (SLE) as the most prevalent CTD (68%), while Sjögren’s syndrome was the least common (1%). Among ENA specificities, U-RNP antibodies showed the highest frequency (56.9%), whereas PM-Scl antibodies were least frequent (1%). Although IIF remains the gold standard for ANA detection, ELISA is a useful initial screening tool, as IIF may fail to detect low-positive ANA cases identified by ELISA. Interpretation of ANA positivity should always be made in appropriate clinical context and confirmed by more specific tests such as ENA profiling. The observed geographical variation in ENA antibody frequency and CTD patterns highlights the need for further region-specific studies to better define antibody prevalence in CTDs.