Anti-Saccharomyces cerevesie antibodies (ASCA IgG)

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Antibodies against yeast antigens.

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Anti-Saccharomyces cerevisiae Antibodies (ASCA IgG) - Comprehensive Test Guide

Why is it done?
- Detects IgG antibodies against Saccharomyces cerevisiae, a common baker's yeast, which serves as a marker for immune dysfunction in the gastrointestinal tract
- Primary indication: Diagnosis and assessment of Crohn's disease, particularly to help differentiate inflammatory bowel disease (IBD) subtypes
- Evaluates intestinal barrier function and immune response to microbial antigens in patients with chronic gastrointestinal symptoms
- Ordered when patients present with unexplained chronic diarrhea, abdominal pain, weight loss, or other symptoms suggestive of IBD
- Typically performed during initial evaluation of suspected inflammatory bowel disease or when differentiating between Crohn's disease and ulcerative colitis
- May be used to assess disease activity, severity, and prognosis in established IBD cases
Normal Range
- Normal (Negative) Result: < 1.4 ELISA Units (EU) or < 1.0 Optical Density Index (ODI) - indicates absence of IgG antibodies to yeast
- Borderline/Equivocal: 1.4-2.0 EU or 1.0-1.2 ODI - suggests possible immune response; may warrant repeat testing or clinical correlation
- Positive/Abnormal: > 2.0 EU or > 1.2 ODI - indicates presence of IgG antibodies against Saccharomyces cerevisiae
- Units of measurement: ELISA Units (EU/mL) or Optical Density Index (ODI); reference ranges may vary slightly between laboratories
- Normal results in healthy individuals suggest intact intestinal barrier and normal immune tolerance to commensal yeast organisms
- Positive results indicate abnormal immune response to yeast antigens, suggesting compromised intestinal barrier function
Interpretation
- Positive ASCA IgG (with or without ASCA IgA): Strongly associated with Crohn's disease; found in approximately 50-70% of Crohn's disease patients and 5-15% of healthy controls
- ASCA positive + pANCA negative: Most typical serological pattern in Crohn's disease; helps differentiate from ulcerative colitis
- ASCA positive + pANCA positive: Unusual pattern; suggests severe or atypical IBD, possible overlap features, or increased disease severity
- Negative ASCA IgG with positive ASCA IgA: May indicate early disease or mucosal-level immune response; requires clinical correlation
- Negative result in suspected IBD: Does not exclude Crohn's disease (approximately 30-50% of Crohn's patients are ASCA negative); may suggest ulcerative colitis or other diagnoses
- Factors affecting results: Disease duration (typically longer-standing disease shows higher positivity), disease location (colonic vs ileal), genetic predisposition, concurrent infections, and immune status
- Clinical significance: ASCA positivity correlates with increased risk of complications including fistulas, strictures, and need for surgery; may indicate more aggressive disease phenotype
- ASCA IgG persists longer than ASCA IgA and may remain positive even during periods of disease remission, reflecting past immune activation
- Can be found in other conditions including celiac disease, systemic lupus erythematosus, and other autoimmune conditions, though less common
Associated Organs
- Primary organ system: Gastrointestinal tract, particularly the small intestine (terminal ileum) and colon; immune system with focus on intestinal barrier function
- Crohn's Disease: Primary condition associated with ASCA positivity; chronic transmural inflammation of bowel; increased risk of complications in ASCA-positive patients
- Ulcerative Colitis: Typically ASCA-negative; helps differentiate from Crohn's disease when combined with other serological markers
- Intestinal complications associated with ASCA positivity: Fistulae (internal and perianal), strictures, bowel obstruction, perforation, and increased need for surgical intervention
- Extraintestinal manifestations potentially associated: Arthralgia, pyoderma gangrenosum, erythema nodosum, uveitis, primary sclerosing cholangitis
- Related conditions: Indeterminate colitis, irritable bowel syndrome (though ASCA usually negative), celiac disease, and other autoimmune gastrointestinal conditions
- Systemic complications: Increased susceptibility to infections due to compromised intestinal barrier; malabsorption leading to nutritional deficiencies
Follow-up Tests
- ASCA IgA testing: Complements IgG; helps assess disease activity and mucosal immune response; often declines with successful treatment
- pANCA (perinuclear antineutrophil cytoplasmic antibodies): Helps differentiate between Crohn's disease (typically negative) and ulcerative colitis (positive in 60-80%); part of comprehensive IBD serology panel
- Inflammatory markers: C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) to assess current disease activity and inflammation
- Fecal calprotectin: Marker of intestinal inflammation; helps assess bowel inflammation independent of systemic markers
- Colonoscopy with biopsy: Definitive diagnostic procedure to visualize inflammation, confirm diagnosis, assess disease extent, and obtain tissue samples
- Imaging studies: CT enterography or MR enterography to assess disease extent, detect complications (strictures, fistulas), and evaluate extraenteric manifestations
- Complete blood count (CBC): Detects anemia from chronic disease or intestinal blood loss, assesses for leukocytosis indicating active inflammation
- Comprehensive metabolic panel: Assesses hepatic and renal function, electrolyte balance, and identifies malabsorption-related abnormalities
- Additional autoimmune serology: ANA, tissue transglutaminase (for celiac disease) to rule out other autoimmune conditions with similar presentations
- Repeat ASCA testing: Not routinely recommended for monitoring; remains relatively stable; useful for prognostication at baseline
- Monitoring frequency: Initial comprehensive evaluation followed by periodic reassessment based on clinical response to therapy; more frequent monitoring if disease active or complications develop
Fasting Required?
- Fasting Required: No
- This is a serological test that detects antibodies in blood serum and does not require fasting; food intake does not affect antibody levels or test accuracy
- Sample collection: Venipuncture for serum collection; can be performed at any time of day
- Patient preparation: No special preparation needed; patient may eat and drink normally before testing
- Medications: No medications need to be avoided for this test; continue all regular medications as prescribed by physician
- Special instructions: Inform phlebotomist of any recent infections or immunizations, as these may theoretically affect immune markers; wear loose-fitting clothing for easy arm access
- Timing considerations: Test can be performed anytime; optimal timing is during initial evaluation or when clinically indicated; no specific time-of-day effect on results

How our test process works!