The anti-Saccharomyces cerevisiae antibody assay in a province-wide practice: accurate in identifying cases of Crohn's disease and predicting inflammatory disease.

OBJECTIVE: To determine the utility of the anti-Saccharomyces cerevisiae antibody (ASCA) ELISA test developed in Manitoba in 2001 in a population-wide sample referred from physicians across Manitoba in their investigation of patients with gastrointestinal symptoms.
METHODS: Patients whose serum was referred for ASCA testing in 2001 and 2002 were eligible for the present study. ELISA was performed by a technologist, blind to patient diagnoses. A single investigator contacted physicians to facilitate chart review. Data collected included demographics, final diagnoses and tests used to substantiate the final diagnosis.
RESULTS: Of 482 subjects identified, 410 charts were available for review and 29 of those were unavailable for follow-up or had incomplete charts. The present study population included Crohn's disease (CD, n=114), ulcerative colitis (n=74), indeterminate colitis (n=31), celiac disease (n=9), irritable bowel syndrome (n=75), other diagnoses (n=33) and no disease (n=45). ASCA had a sensitivity of 37% (95% CI 27.8 to 46.8) and specificity of 97% (95% CI 93.8 to 98.6) for diagnosing CD and an odds ratio for a diagnosis of CD of 18.4 (95% CI 8.2 to 41.3). The 47 ASCA-positive patients included the following diagnoses: CD=39, ulcerative colitis=3, indeterminate colitis=1, celiac disease=3 and no disease=1. The likelihood of having an inflammatory disease if ASCA is positive was nearly 40-fold.
CONCLUSION: A positive ASCA test using this assay nearly clinches a diagnosis of some form of inflammatory intestinal disease, which is highly likely to be CD. In symptomatic patients, a positive ASCA test should encourage the clinician to pursue further investigations.