A cost-effective assessment for the combination of indirect immunofluorescence and solid-phase assay in ANA-screening

Anti-nuclear antibodies (ANA) testing on indirect immunofluorescence (IIF) has been for a long time the gold standard assay in the diagnosis of rheumatic diseases; more recently different solid phase assays (SPA) have been recommended to increase specificity of positive results. The best combination of the different assays should both reduce the time to diagnosis and the costs of testing.

Serum samples from 995 unselected outpatients were analysed simultaneously using IIF and a fluorescent enzyme SPA as initial screening test. Any IIF or SPA positive sample was further analysed for individual antibody specificities and three algorithm models with different timelines were adopted. The cost-effectiveness assessment was performed by calculating the total number of positive patients and the cost of diagnosis for each algorithm.

IIF and SPA were both positive in 112 (11.3 %) patients, and both negative in 597 (60 %) patients; 257 results (25.8 %) were conflicting between the two methods. The three algorithms resulted in a different number of positive patients and had a different cost per single diagnosis: the combined algorithm revealed the highest number of positive patients with a lower cost per diagnosis than the traditional one.

The combined approach of two different methods ensures the highest reliability of ANA screening test; however, specific appropriate SPA testing might be chosen according to IIF pattern as recommended in International guidelines. Each clinical laboratory should carefully evaluate its diagnostic algorithm for ANA testing on the volume and type of requests, eventually designing new cost-effective reimbursement models based on patients outcomes.