Development of an assay for antibodies to Saccharomyces cerevisiae: Easy, cheap and specific for Crohn's disease

OBJECTIVE: To develop a serological test to measure antibodies to Saccharom yces cerevisiae in patients with inflammatory bowel disease. METHODS: An ELISA to the mannan of S cerevisiae that is commercially availa ble was developed. Sera were tested from randomly chosen sera specimens kep t frozen at the University of Manitoba Inflammatory Bowel Disease Clinical and Research Centre, Winnipeg, Manitoba. Clinical diagnoses were kept blind ed until the assay results were finalized. One hundred thirty-six sera were tested, including 51 with Crohn's disease, 32 with ulcerative colitis, one with indeterminate colitis and 16 other control subjects. Thirty-six sampl es were duplicates from patients already studied but were either run on sep arate days or drawn on different days. RESULTS: Using a cutoff of 15 binding units as a positive result, Crohn's d isease was found to have a sensitivity of 53% but a specificity of 100% com pared with ulcerative colitis. Compared with all other diagnoses (including ulcerative colitis), Crohn's disease had a sensitivity of 53% and a specif icity of 96%. For patients with Crohn's disease only, those who were anti-S cerevisiae antibody (ASCA) positive (n=27) were significantly more likely to have proximal gastrointestinal disease and significantly less likely to have colonic or inflammatory type disease than those who were ASCA negative (n=24). The direct cost of this assay was $6.00 per positive test, and the total charge was set at $38.15. CONCLUSIONS: A reasonably inexpensive, easy and reproducible assay to asses s for antibodies to S cerevisiae has been developed. Using a cutoff for pos itivity of 15 binding units, this test had a specificity of 100% for ruling out Crohn's disease and a lower (60%) sensitivity compared with ulcerative colitis. This test could identify a specific phenotype of patients with Cr ohn's disease as being more likely to have small bowel Crohn's disease and less likely to have colonic (isolated) or inflammatory disease, as opposed to fibrostenotic disease or penetrating disease. The test proved reliable w hen assaying samples drawn or assayed on different days.