What does a positive Saccharomyces cerevisiae (baker's yeast) Immunoglobulin G (IgG) and equivocal Immunoglobulin A (IgA) result indicate?

Interpretation of Saccharomyces cerevisiae Antibody Results

Your results show positive IgG antibodies (31.4 U) and equivocal IgA antibodies (27.5 U) to Saccharomyces cerevisiae (baker's yeast), which are most commonly associated with inflammatory bowel disease, particularly Crohn's disease, though they can also be elevated in celiac disease and require further gastrointestinal evaluation to determine the underlying cause. 1

What These Results Mean

Anti-Saccharomyces cerevisiae Antibodies (ASCA)

• IgG ASCA at 31.4 U is positive (threshold ≥25.0 U), indicating an immune response to baker's yeast that is characteristic of certain gastrointestinal conditions 2
• IgA ASCA at 27.5 U is equivocal (borderline range 20.1-24.9 U), suggesting a developing or mild immune response 1

Primary Disease Associations

Crohn's Disease (Most Common)

• ASCA IgG is positive in approximately 50-65% of Crohn's disease patients, with specificity around 90% 2, 3
• ASCA IgA is positive in 28-34% of Crohn's disease patients 4, 3
• Patients with small bowel Crohn's disease have significantly higher IgG antibody levels than those with colonic disease 2
• The combination of positive ASCA IgG with equivocal/positive IgA increases the likelihood of Crohn's disease 3

Celiac Disease (Secondary Association)

• ASCA IgG is elevated in 18-61% of celiac disease patients at diagnosis, with adults showing higher positivity rates (61%) than children (18%) 4, 2
• Importantly, ASCA antibodies typically disappear during a gluten-free diet in celiac disease patients, with 99% of children and 71% of adults becoming ASCA-negative after dietary treatment 4
• This distinguishes celiac disease from Crohn's disease, where ASCA remains persistently elevated 4

Other Conditions

• ASCA is positive in only 0-5% of healthy controls 4
• Ulcerative colitis patients show ASCA levels similar to healthy controls 2, 3
• Intestinal tuberculosis can also show elevated ASCA, making it difficult to distinguish from Crohn's disease serologically 3

Recommended Next Steps

Essential Gastrointestinal Evaluation

• Proceed with ileocolonoscopy and biopsies to evaluate for inflammatory bowel disease, particularly Crohn's disease, as this is the most likely diagnosis given your antibody pattern 1
• Perform upper endoscopy with duodenal biopsies to rule out celiac disease, especially if you have any gastrointestinal symptoms 1

Complete Celiac Disease Panel

• Measure IgA tissue transglutaminase (tTG) antibodies and assess for IgA deficiency, as IgA deficiency occurs in 1-3% of celiac disease patients and would affect test interpretation 5, 1
• If IgA deficient, perform IgG-based testing with IgG tTG and IgG deaminated gliadin peptides 1

Additional Testing

• Fecal calprotectin or lactoferrin to assess for intestinal inflammation, which would support inflammatory bowel disease 1
• Stool testing for Giardia (antigen test or PCR) to exclude infectious causes 1
• HLA DQ2/DQ8 testing if celiac disease is strongly suspected despite negative serology 1

Clinical Significance and Monitoring

If Crohn's Disease is Diagnosed

• Management should be guided by disease location, severity, and complications 1
• ASCA levels remain persistently elevated and do not normalize with treatment 4

If Celiac Disease is Diagnosed

• Strict adherence to a gluten-free diet is essential 1
• ASCA antibodies should disappear within months of starting a gluten-free diet, particularly in younger patients 4
• Monitor with anti-TG2 IgA serology to assess dietary adherence 1
• Persistently positive ASCA after gluten-free diet suggests either poor dietary adherence or that Crohn's disease may be the actual diagnosis 4

Important Caveats

Diagnostic Limitations

• ASCA cannot differentiate between Crohn's disease and intestinal tuberculosis, so if you have risk factors for tuberculosis (endemic area, exposure history), this must be specifically evaluated 3
• ASCA IgG is characteristic but not specific to Crohn's disease, as it can be elevated in celiac disease and other conditions 2
• The presence of both IgG and IgA ASCA increases diagnostic specificity but does not eliminate the need for endoscopic confirmation 3

Do Not Start Treatment Before Diagnosis

• Never start a gluten-free diet before completing the diagnostic workup, as this will cause celiac serology to become falsely negative and biopsies to be inconclusive 5, 6
• Continue eating gluten-containing foods until all testing is complete 5