Antinuclear Antibody Tests Analyzed for Screening Autoimmunity

An evaluation has been made of the various blood tests used to detect antinuclear antibodies (ANA) that facilitate the diagnosis of connective tissue diseases.

An indirect fluorescent antibody (IFA) test was compared with four enzyme-linked immunosorbent assays for their diagnostic performance and usefulness in detecting and characterizing the titers of ANA in various pathological conditions.

A team of scientists, collaborating with the ARUP laboratories (Salt Lake City, UT, USA), screened 224 clinically defined serum samples consisting of 30 from systemic lupus erythematous (SLE) cases, 94 from rheumatoid arthritis cases, and 100 from healthy donors plus 495 serum samples submitted for routine ANA testing and 12 reference serum samples. The IFA assay used was the NOVA Lite HEp-2 ANA, which uses an immunoglobulin G (IgG) heavy chain–specific conjugate. The four ELISAs tested were the Aeskulisa ANA HEp-2, the Bio-Rad ANA Screen, the Phadia Varelisa ANA 8 Screen, and the QUANTA Lite ANA ELISA.

Although none of the four ANA ELISAs were formulated in the same way, they all contained the same antigens and disrupted substrate except for the Varelisa ANA 8 screen assay (Phadia; Uppsala, Sweden), which did not contain the substrate. The clinical samples were selected serum samples previously sent to ARUP Laboratories for ANA testing, of which 50 were negative and 445 were positive by the Bio-Rad ANA ELISA (Bio-Rad; Hercules, CA, USA). The sensitivities of the ELISA assays ranged from 90% to 97% compared with 80% by IFA in the SLE serum samples. However, the specificities of the ELISA assays ranged from 36% to 94%, whereas the IFA had 99% specificity.

The NOVA Lite HEp-2 ANA IFA assay and the QUANTA Lite ANA ELISA are products of INOVA Diagnostics (San Diego, CA, USA). The Aeskulisa ANA HEp-2 is a product of Aesku Diagnostics  (Wendelsheim, Germany). The authors concluded that overall ELISAs for ANA assays demonstrated better sensitivity and good specificity, suggesting ELISA is a more cost-effective alternative to IFA testing for initial ANA screening. Samples positive by ANA ELISA should be tested on HEp-2 to determine the titer and pattern. The study was published in May 2011 in the American Journal of Clinical Pathology.

Related Links:
ARUP laboratories
Phadia
Bio-Rad