Objective: The objective of this study was to determine whether characteristics of positive results in the indirect immunofluorescence assay on HEp-2 cells for anti-cell antibodies (HEp-2 IFA) differ between patients with non-autoimmune diseases (NADs) and patients with systemic autoimmune rheumatic diseases (SARDs).
Methods: Cross-sectional observational study comparing HEp-2 IFA test results in three groups: (a) 558 NAD patients comprising four subgroups (cancer ( n = 95), infectious diseases ( n = 148), psychiatric diseases ( n = 163), common non-infectious chronic diseases ( n = 152)); (b) 194 SARD patients; (c) 1217 healthy individuals (HIs). Sera were tested at 1:80 dilution and diluted to the end titer. Slides were analyzed by two independent blinded examiners.
Results: A positive HEp-2 IFA test occurred in 102 (18.3%) NAD patients, 170 (87.6%) SARD patients and 150 (12.3%) HIs. The four NAD subgroups did not differ regarding HEp-2 IFA frequency, titer or pattern. HEp-2 IFA titer was higher in NAD patients than in HIs and both had lower titer than SARD patients. Nuclear dense fine speckled pattern was more frequent in NAD patients and HIs than in SARD patients ( p < 0.001). Nuclear homogeneous and nuclear coarse speckled patterns were more frequent in SARD patients than in the other groups ( p < 0.001). The nuclear fine speckled pattern was prevalent in all three groups, but presented a gradient in titer across them; HIs and NAD patients had low and intermediary titers, which were significantly lower than in SARD patients ( p < 0.001).
Conclusion: Positive HEp-2 IFA frequency, pattern and titer present differential features in NAD and SARD patients, and this attribute adds value to the test in the diagnosis of SARDs.
Keywords: Antinuclear antibodies; autoantibodies; autoimmune diagnosis; autoimmune diseases; systemic lupus erythematosus.