Low positive rate of serum autoantibodies in colorectal cancer patients without systemic rheumatic diseases

Background: Antinuclear antibody (ANA) testing is useful for screening, diagnosis and follow-up of patients with systemic rheumatic diseases. Indirect immunofluorescence (IIF) on HEp-2 cells is the gold standard for ANA testing. However, ANA have also been detected in patients with different cancer types but without any autoimmune disease. To overcome these shortcomings, different automated solid-phase assays have been developed. Aim: To determine the positive rate of a new ANA detection method (EliA CTD Screen, Phadia, Germany), in CRC patients without systemic rheumatic diseases. Additionally, we compare this method with IIF. Materials and methods: Serum samples were obtained before a colonoscopy procedure in a patient cohort (n=186) with a high clinical suspicion of CRC. Samples for ANA detection in CRC patients were processed in parallel by IIF on HEp-2 and the solid-phase fluoroenzymeimmunoassay EliA CTD Screen (Phadia, Germany) on the Phadia 250 instrument (Phadia GmbH, Freiburg, Germany). Positive samples by IIF and/or CTD were tested with EliA single ANA assays (Phadia, Germany) on the Phadia 250 instrument (Phadia GmbH, Freiburg, Germany). Results: Forty-five patients diagnosed with CRC were included. Four cases were positive by CTD and 23 by IIF. Of the four positive patients by CTD, two were positive and one indeterminate for anti-dsDNA antibodies. Of the 23 positive by IIF, one patient was positive and another indeterminate for anti-dsDNA antibodies, and a third patient was positive for anti-U1RNP antibodies. Conclusions: The CTD assay shows a low false positive rate for detecting autoantibodies in a clinical context of CRC.