![]() Manufacturers of solid-phase assays attempt to improve the performance of the assays by adding extra purified recombinant antigens. However, previous reports showed that solid-phase assays still have lower sensitivity when compared to indirect immunofluorescence 8. Determining the correct dilutional titer depends on the experience of the technician who is reading the immunofluorescence slides.įor the last two decades, ANA testing with ELISA technique has been introduced aiming to save time and efforts needed for ANA-IIF and trying to improve the performance of the ANA testing. Despite the good sensitivity of the test, ANA-IIF has some limitations it is a time-consuming, labor-intensive and operator dependent test. It was found that the clinical significance of the test rises with increasing titers 5, 6, as well as with the identification of the responsible specific autoantigen 7. Overall, it is recommended that the serum dilution that gives a specificity of 95% in healthy individuals should be used as the cut-off 4. At a titre of 1:40 serum dilution, 25–30% of healthy individuals might test positive for ANA, which increases with age 2, 3. It has poor specificity and low positive predictive value especially when low titers are used as a cutoff. ![]() ANA-IIF is the current endorsed technique for ANA detection by the American and Europeans rheumatology Societies (ACR and EULAR). The two main methods to detect ANA are the indirect immunofluorescence ANA-IIF and the ELISA technique. It can be false positive as well in other circumstances such as non-autoimmune diseases like cancers, infections, in patients taking certain medications like antiepileptics and antiarrhythmics and in asymptomatic first-degree relatives of patients with autoimmune diseases 1. The test can be positive in many autoimmune conditions other than CTDs such as autoimmune hepatitis, primary biliary cirrhosis, Hashimoto thyroiditis Etc. The clinical performance of ANA-ELISA for CTDs screening showed better sensitivity and specificity as compared to the conventional ANA-IIF in our cohort.Īntinuclear antibody detection by indirect immunofluorescence technique (ANA-IIF) is a valuable screening tool for autoimmune connective tissue diseases (CTDs), though it is non-specific. The overall specificity of ANA-ELISA was 89.05%, which was slightly better than ANA-IIF 86.72%. For the SLE it was 64.3% vs 76.9%, Sjogren’s Syndrome was 50% vs 76.9% respectively. At a cut-off ratio ≥ 1.0 for ANA-ELISA and a dilutional titre ≥ 1:80 for ANA-IIF, the sensitivity of ANA-IIF and ANA-ELISA for all CTDs were 63.3% vs 74.8% respectively. 1457 patients were assessed by the rheumatologist and included in the analysis. Between March and December 2016, a total of 12,439 ANA tests were requested. The electronic medical record of these patients was reviewed looking for CTD diagnosis documented by the Senior rheumatologist. During the period between March till December 2016 all requests for ANA from primary, secondary, and tertiary care centers were processed with both techniques ANA-IIF and ANA-ELISA. ![]() ANA-ELISA is a solid-phase immune assay includes 17 ANA-targeted recombinant antigens dsDNA, Sm-D, Rib-P, PCNA, U1-RNP (70, A, C), SS-A/Ro (52 and 60), SS-B/La, Centromere B, Scl-70, Fibrillarin, RNA Polymerase III, Jo-1, Mi-2, and PM-Scl. We investigated the performance of ANA-ELISA for CTDs screening and diagnosis and comparing it to the conventional ANA-IIF. ![]()
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