Sera from patients suffering from Crohn's and other diseases and from healthy subjects were tested for agglutinins to anaerobic, gram-positive coccoid rods belonging to species of Eubacterium and Peptostreptococcus. Four strains labelled Eubacterium contortum (two strains), Eubacterium rectale and Peptostreptococcus productus were agglutinated by a higher percentage of sera from patients with Crohn's disease than from healthy subjects and from patients with liver and intestinal diseases (including ulcerative colitis), ankylosing spondylitis, granulomatous diseases, diseases of immunity and malignancies.
The agglutinins were of the IgG and IgM classes and strain-specific; the titres were low.
The results obtained with sera from patients with Crohn's disease and healthy people were subjected to discriminant analysis to estimate the probability, based on the combined results with the four strains, that a patient suffers from Crohn's disease. When sera giving an a posteriori probability ≥ 0·95 (a priori probability = 0·5) were considered positive, the test with four strains had a sensitivity of 54% and a, specificity of nearly 100%. The results with sera submitted for diagnosis showed that positive reactions in patients with a diagnosis apparently incompatible with Crohn's disease were within acceptable limits.