Analysis of Antinuclear Antibody Test Referral Patterns in a Tertiary Care Hospital over Three Years: A Retrospective Observational Study

Abstract

Introduction: Antinuclear Antibodies (ANA) detection by Human Epithelial Substrate (Hep2) is the recommended screening test for the diagnosis of ANA-Associated Rheumatic Diseases (AARD). ANA is ordered by various specialists in a tertiary care hospital, and a positive ANA result is followed by testing for specific autoantibodies. High pretest probability, pattern type with intensity, and referral departments are key factors determining the autoimmune diagnosis. Aim: To analyse the ANA referral patterns among the various departments and also to estimate the prevalence and clinical significance of rare ANA patterns. Materials and Methods: A retrospective observational study was conducted at Nizam's Institute of Medical Sciences, Hyderabad, a tertiary care hospital, in Hyderabad, Telangana, India where ANA test reports (n=16,994) from various departments over three years (November 2017 to October 2020) were evaluated between November 2022 to December 2022. ANA tests were performed on Hep2 substrate at a 1:100 dilution, and ANA patterns were reported according to the International Consensus on ANA Patterns (ICAP) nomenclature. Statistical analysis of department- wise ANA positivity and fluorescence intensity was conducted, and the final diagnoses of patients with rare ANA patterns (<1%) were noted from clinical records. Fischer's-exact test was used for comparing categorical variables, considering p-value <0.05 as statistically significant. Results: The majority of ANA requests were from the Rheumatology department (5859; 34.5%), followed by nephrology (3132; 18.4%), neurology (1940; 11.4%), general medicine (1646; 9.7%), haematology (1106; 6.5%), and casualty (878; 5.2%), accounting for 85.6% of total referrals. The highest percentage of positivity among ANA referrals was observed in Rheumatology (333; 5.7%), with 58% of positive ANA showing 4+ intensity. No positives were observed from many surgical departments. Rare ANA patterns with a prevalence of less than 1% were observed in 22 patients with mitotic patterns accounting for the majority of rare patterns seen in 11 out of 22 (50%) cases followed by nuclear envelope, rods rings, and nuclear dense fine speckled patterns were observed in six, four, and one patient(s), respectively. The majority of rare ANA patterns had 2+ fluorescence intensity without any associated autoimmune diagnosis. Conclusion: The highest and lowest positivity among ANA referrals were observed in the rheumatology and surgical departments, respectively. Considering the pretest probability of AARD before ordering an ANA test would lead to the optimum utilisation of laboratory services. Mitotic patterns constituted the majority of rare ANA patterns and need to be clinically correlated with antibody titers.