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Unit Code 83022:
Saccharomyces cerevisiae Antibody, IgA, Serum

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Useful For

Helping clinicians distinguish between ulcerative colitis and Crohn's

disease in patients suspected of having inflammatory bowel disease

Clinical Information

The term inflammatory bowel disease (IBD) is often used to refer

to 2 diseases, ulcerative colitis (UC) and Crohn's disease (CD), that

produce inflammation of the large or small intestines. 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.(1)

Patients with UC often have measurable neutrophil-specific

antibodies (NSA), 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

Negative: 0.0-20.0 U

Equivocal: 20.1-24.9 U

Weakly positive: 25.0-34.9 U

Positive: > or =35.0 U

Interpretation

Antibodies to Saccharomyces cerevisiae antigen (ASCA) results

cannot be interpreted without also considering #82966 "Neutrophil

Specific Antibodies, Serum" results.

  

The finding of NSA with normal levels of IgA and IgG ASCA is

consistent with the diagnosis of UC; the finding of negative NSA

with elevated IgA and IgG ASCA is consistent with 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 (PV) for UC and CD,

respectively: (2)

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

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

Cautions

ASCA and NSA are useful adjuncts in the diagnosis of UC and 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 NSA, and some patients

with UC have elevated levels of IgA and/or IgG ASCA. Approximately

1/3 of patients have low titered antinuclear antibodies (ANA), which

make it impossible to distinguish the presence or absence of NSA.

These results are reported as indeterminate.

  

Measurement of ASCA and NSA are not useful to determine the

extent of disease in patients with IBD or to determine the response

to disease-specific therapy including surgical resection of

diseased intestine.

Clinical Reference

1.   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

 

2.   Homburger, HA; Unpublished Mayo information

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