Test Catalog

Test ID: GASCA    
Saccharomyces cerevisiae Antibody, IgG, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Helping clinicians distinguish between ulcerative colitis and Crohn disease in patients suspected of having inflammatory bowel disease by identifying Saccharomyces cerevisiae IgG antibody.


Measurement of anti-Saccharomyces cerevisiae antibodies (ASCA) and neutrophil-specific antibodies (NSA) are not useful to determine the extent of disease in patients with inflammatory bowel disease or to determine the response to disease-specific therapy including surgical resection of diseased intestine.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Inflammatory bowel disease (IBD) refers to 2 diseases, ulcerative colitis (UC) and Crohn disease (CD), which produce inflammation of the large or small intestines.(1) The diagnoses of both diseases are based on clinical features, radiographic findings, colonoscopy, mucosal biopsy histology, and, in some cases, operative findings and resected bowel pathology and histology.


Recently, patients with IBD have also been shown to have antibodies in serum that help distinguish between CD and UC.(2) Patients with UC often have measurable neutrophil-specific antibodies (NSA) that react with as yet uncharacterized target antigens in human neutrophils; whereas patients with CD often have measurable antibodies of the IgA and/or IgG isotypes that react with cell wall mannan of Saccharomyces cerevisiae strain Su 1.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative: < or =20.0 U

Equivocal: 20.1-24.9 U

Weakly positive: 25.0-34.9 U

Positive: > or =35.0 U

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

The finding of neutrophil-specific antibodies (NSA) with normal levels of IgA and IgG anti-Saccharomyces cerevisiae antibodies (ASCA) is consistent with the diagnosis of ulcerative colitis (UC); the finding of negative NSA with elevated IgA and IgG ASCA is consistent with Crohn disease (CD).


NSA are detectable in approximately 50% of patients with UC.


Elevated levels of either IgA or IgG ASCA occur in approximately 55% of patients with CD. Elevated levels of both IgA and IgG ASCA occur in approximately 40% of patients with CD.


Employed together, the tests for NSA and ASCA have the following positive predictive values (PPV) for UC and CD, respectively:(2)

-NSA-positive with normal levels of IgA and IgG ASCA, PPV of 91%

-NSA-negative with elevated levels of IgA and IgG ASCA, PPV of 90%

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Saccharomyces cerevisiae IgG antibodies (ASCA) are useful as an adjunct in the evaluation of patients with inflammatory bowel disease, and should not be relied upon exclusively to establish the diagnosis of ulcerative colitis (UC) or Crohn disease (CD), or to distinguish between these 2 diseases. Saccharmocyes cerevisiae IgA and IgG antibodies are most useful for distinguishing between UC and CD when assessed in conjunction with neutrophil-specific antibodies (NSA).


Some patients with CD have detectable neutrophil-specific antibodies and some patients with UC have elevated concentrations of IgA and/or IgG anti-Saccharomyces cerevisiae antibodies.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. The Autoimmune Diseases: Inflammatory Bowel Diseases. Edited by NR Rose, IR Mackay. New York, Elsevier Academic Press, 2008

2. Sandborn WJ, Loftus EV Jr, Homburger HA, et al: Evaluation of serological disease markers in a population-based cohort of patients with ulcerative colitis and Crohn's disease. Inflamm Bowel Dis 2001 Aug;7(3):192-201