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Test ID: AASCA    
Saccharomyces cerevisiae Antibody, IgA, Serum

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

Helping clinicians distinguish between ulcerative colitis and Crohn’s disease in patients suspected of having inflammatory bowel disease

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's disease (CD), that produce inflammation of the large or small intestines.(1) The diagnoses of both diseases are based on clinical features, the results of barium X-rays, colonoscopy, mucosal biopsy histology, and in some cases operative findings and resected bowel pathology and histology.

 

Recently, patients with IBD have been shown to have antibodies in serum that help distinguish between CD and UC.(2) Patients with UC often have measurable neutrophil-specific antibodies, which 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, which 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: 0.0-20.0 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

In IBDP / Inflammatory Bowel Disease Serology Panel, Serum, anti-Saccharomyces cerevisiae antibodies (ASCA) and neutrophil-specific antibodies (NSA) are measured. The finding of NSA with normal levels of IgA and IgG 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's 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.

 

Approximately 40% of patients with CD have elevated levels of both IgA and IgG ASCA.

 

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

IBDP / Inflammatory Bowel Disease Serology Panel, Serum is useful as an adjunct in the diagnosis of ulcerative colitis (UC) and Crohn’s disease (CD), but should not be relied upon exclusively to establish the diagnosis of UC or CD, or to distinguish between these 2 diseases. Some patients with CD have detectable neutrophile-specific antibodies (NSA), and some patients with UC have elevated levels of IgA and/or IgG anti-Saccharomyces cerevisiae antibodies (ASCA).

 

Measurement of ASCA and 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 Reference Provides recommendations for further in-depth reading of a clinical nature

1. The Autoimmune Diseases: Inflammatory Bowel Diseases. Edited by NR Rose, IR Mackay. New York, NY, 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