ASCA IgA (Anti-Saccharomyces cerevisiae Antibody, IgA)

Serum

Other names: ASCA IgA, ASCA (IgA), Anti-Saccharomyces cerevisiae Antibody IgA, Anti-Saccharomyces cerevisiae Antibodies IgA, Saccharomyces cerevisiae IgA, Saccharomyces cerevisiae Antibody IgA, S. cerevisiae IgA, Anti-yeast antibody IgA, ASCA immunoglobulin A

Optimal Result: 0 - 20 Units.

IBD Expanded Panel (Inflammatory Bowel Disease)

From Healthmatters.io Team and reviewed by HM Editorial Team

Written on July 2, 2026 | Last updated Updated on July 2, 2026

Lab Results Explained and Tracked

What ASCA IgA measures

ASCA IgA measures IgA-class antibodies against mannan, a carbohydrate in the cell wall of Saccharomyces cerevisiae — the yeast used in baking and brewing. Despite showing up in an autoimmune-type condition, ASCA is not an autoantibody: it targets a yeast (dietary and gut) antigen, not the body's own tissue. Its presence is thought to reflect a loss of immune tolerance to microbial antigens at the gut barrier, which is why it's informative in inflammatory bowel disease.

ASCA is measured in two antibody classes, IgA and IgG. They're reported separately because testing both catches more cases: about 80% of people with Crohn's disease are positive for ASCA IgA, ASCA IgG, or both. This page covers the IgA class; the companion measurement is ASCA IgG.

Why it's tested

ASCA IgA is ordered as part of an inflammatory bowel disease (IBD) work-up, usually together with atypical pANCA. The two markers point in opposite directions:

ASCA-positive / pANCA-negative leans toward Crohn's disease
ASCA-negative / pANCA-positive leans toward ulcerative colitis

Used together, this combination can reach a specificity as high as ~99% for separating Crohn's from ulcerative colitis. It's a less invasive adjunct to the diagnostic gold standard (endoscopy with biopsy), not a replacement for it.

What the numbers mean

ASCA IgA is reported against a threshold, with results classed as negative or positive (see the reference range and tiers). Roughly:

Crohn's disease: frequently positive
Ulcerative colitis: positive in fewer than ~2% of cases (IgA)
Healthy people: positive in fewer than ~5% (and essentially never positive for both IgA and IgG at once)

Because a small share of healthy people and some people with other gut conditions (including celiac disease) can test positive, ASCA IgA is interpreted in context — never as a standalone diagnosis.

What to do next

A positive or negative ASCA IgA is one input, not a verdict. Results should be reviewed by your clinician alongside symptoms, other IBD markers, and endoscopic or imaging findings. If you were tested because of ongoing digestive symptoms, bring the full panel — ASCA IgG, pANCA, and any glycan markers — to that conversation rather than a single value.

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What does it mean if your ASCA IgA result is too high?

A positive (elevated) ASCA IgA means IgA antibodies to Saccharomyces cerevisiae were detected above the lab's threshold. This pattern is seen far more often in Crohn's disease than in ulcerative colitis, so a positive result raises the likelihood of Crohn's — particularly when ASCA IgG is also positive and pANCA is negative.

A positive ASCA IgA does not by itself confirm Crohn's disease: some people with ulcerative colitis, celiac disease, or no IBD at all can test positive. In people already diagnosed with Crohn's, ASCA positivity is associated with earlier disease onset, small-bowel (ileal) involvement, and a more complicated, aggressive course (strictures, fistulae, or need for surgery). Higher levels and positivity across more markers strengthen that association. Interpretation should always combine this result with clinical findings, endoscopy, and the rest of the IBD panel.

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What does it mean if your ASCA IgA result is too low?

A negative (non-reactive) ASCA IgA means IgA antibodies to Saccharomyces cerevisiae were not detected above the lab's threshold. This does not rule out Crohn's disease — a meaningful share of people with Crohn's are ASCA-negative, and some are positive only for the IgG class. It's worth checking the ASCA IgG result before drawing conclusions.

A negative ASCA IgA is more consistent with the absence of Crohn's-type serology, and in the right clinical picture (especially with a positive pANCA) can support ulcerative colitis over Crohn's. As with a positive, a negative is interpreted alongside the full panel and clinical assessment, not on its own.

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ASCA IgA (Anti-Saccharomyces cerevisiae Antibody, IgA)

What ASCA IgA measures

Why it's tested

What the numbers mean

What to do next

All Your Lab Results. One Simple Dashboard.

What does it mean if your ASCA IgA result is too high?

All Your Lab Results. One Simple Dashboard.

Import, Track, and Share Your Lab Results Easily

Import, Track, and Share Your Lab Results

What does it mean if your ASCA IgA result is too low?

Article Review & Sources

Bring All Your Lab Results Together — In One Place

Gather Your Lab History — and Finally Make Sense of It

Finally, Your Lab Results Organized and Clear

Advanced Plan

Unlimited Account

Pro Monthly

What's included in a Healthmatters membership

Import Lab Results from Any Source

See Your Health Timeline

Understand What Your Results Mean

Enter Your Lab Reports Yourself — Always Free Enter Your Lab Reports — Always Free

Visualize Your Results

Export Your Complete Lab History in a Single File Export Your Complete Lab History

Comprehensive Data Entry Service for Your Reports Data Entry Service for Your Reports

Securely Share With Anyone You Trust

Let Your Lab Results Tell the Full Story

Once your results are in one place, see the bigger picture — track trends over time, compare data side by side, export your full history, and share securely with anyone you trust.

Bring all your results together to compare, track progress, export your history, and share securely.

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All Your Lab Results.
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