Saccharomyces cerevisiae, IgG (ASCA IgG): Negative, Equivocal and Positive Results

In one sentence

Saccharomyces cerevisiae, IgG reports whether you carry antibodies to common yeast, in three tiers — read it alongside your ASCA IgA, and if your report also shows atypical pANCA, use the broader IBD Profile page.

At a Glance

• What it measures: IgG antibodies to Saccharomyces cerevisiae (ASCA), in Units
• Why it is ordered: to support the differential diagnosis of Crohn's disease and ulcerative colitis
• How it is measured: enzyme immunoassay on serum, from a red-top or gel-barrier tube
• Reported as: negative 0–19.9 · equivocal 20.0–24.9 · positive ≥25.0
• Read with: Saccharomyces cerevisiae IgA
• What it cannot do: diagnose Crohn's disease, or detect a yeast infection

What this test measures

Saccharomyces cerevisiae is baker's and brewer's yeast. This test does not look for the yeast itself. It looks for IgG antibodies your immune system has made against a carbohydrate in the yeast cell wall — meaning it measures an immune response to something from outside the body, not an attack on your own tissue.

Those antibodies are called anti-Saccharomyces cerevisiae antibodies, abbreviated ASCA. Labcorp lists ASCA as a synonym for this test, so the two names refer to the same thing. The panel measures two classes, IgG and IgA. Labcorp 164657 reports the IgG and IgA classes together.

Which Saccharomyces cerevisiae test is on your report?

Several different yeast-antibody tests share similar names and are not interchangeable. Check the panel name printed at the top of your report.

Cutoffs and units are specific to the assay that produced them. A number from one of these tests cannot be compared to a number from another.

Reading your result

The result is semiquantitative — a number, but interpreted against fixed cutoffs rather than a continuous reference range.

Ranges shown are Labcorp's for test 164657. Other laboratories run their own assays with their own cutoffs and units, so the tiers printed on your own report are the ones that apply.

Equivocal is the tier worth understanding. It sits between the two cutoffs, and it is not a diluted version of a positive. It means the measurement landed where the assay cannot distinguish one answer from the other. It is not evidence of Crohn's disease. Interpret it with the companion IgA result and the clinical picture; do not count it as positive.

Two people with the same number

Two people both have an ASCA IgG of 26 Units — positive on this assay.

The first also has a positive IgA, longstanding abdominal pain and weight loss, and is heading for a colonoscopy. Here the serology adds weight to a picture that was already forming from symptoms and clinical assessment.

The second had the panel drawn as part of a broad workup for intermittent bloating, has a negative IgA, and has no other findings. The same number carries far less here — a single positive class, no supporting picture.

The number is identical. What differs is everything around it, which is why the result is not read on its own.

Reading it alongside your other results

This panel gives you two numbers — ASCA IgG and ASCA IgA. Labcorp reports them together; the pair can add context, though it remains nondiagnostic, and a single positive class is interpreted in clinical context.

This table describes patterns clinicians commonly consider. It is not a diagnostic algorithm, and no row substitutes for your clinician's reading of your full picture.

If your report also contains "Atypical pANCA," you likely have the broader Labcorp IBD Profile. Use the ASCA/pANCA page for that three-marker interpretation.

What this test cannot tell you

• Whether you have Crohn's disease. Diagnosis draws on clinical assessment, endoscopy with biopsy, and imaging together. Serology supports; it is not recommended to establish the diagnosis on its own.
• Whether you have a yeast infection. This measures antibodies, not yeast. It has no bearing on candida or thrush.
• Whether you eat too much yeast. Research examining yeast-containing food intake alongside ASCA IgG positivity found no association between them.
• How active your disease is, if you already have a diagnosis. This panel is not used for monitoring activity.
• Much on its own. The companion IgA result is what turns this number into a pattern.

Common interpretation mistakes

• Reading equivocal as a weak positive. It is an unresolved result, not a mild one.
• Reading positive as a Crohn's diagnosis. It is not diagnostic of Crohn's, ulcerative colitis, or IBD.
• Reading negative as excluding Crohn's. A meaningful share of people with IBD are ASCA-negative.
• Confusing this with gASCA. A different, glycan-based assay with its own reference frame.
• Confusing it with a pathogen antibody test. ASCA is not evidence of infection with anything.
• Comparing your number to a friend's from a different laboratory. Units and cutoffs are assay-specific.

Questions your doctor may ask

• What symptoms prompted this test — abdominal pain, diarrhea, blood in stool, weight loss?
• How long has this been going on, and is it constant or in episodes?
• Any family history of Crohn's disease or ulcerative colitis?
• Have you had a colonoscopy or any imaging of the bowel?
• What did the companion ASCA IgA result show?

Read together with

• Saccharomyces cerevisiae, IgA — the companion class on the same panel; the combination is what carries weight
• Fecal calprotectin, CRP — noninvasive markers used to gauge intestinal inflammation
• Atypical pANCA — only if your report is the broader IBD Profile; see the ASCA/pANCA page for that reading

Things that can affect the result

Labcorp rejects specimens showing hemolysis, lipemia, gross bacterial contamination, or that have been heat-treated. Serum is stable for 14 days at room temperature, refrigerated or frozen. If a result does not fit your clinical picture, sample quality is a reasonable thing to ask about.

Clinical pearls

• Labcorp reports IgG and IgA together and notes that, in its cited data, no healthy controls had both classes; the pair adds context but remains nondiagnostic.
• ASCA is directed at a dietary and gut antigen, not at your own tissue — it is not an autoantibody in the way ANA or anti-dsDNA are.
• Crohn's disease is diagnosed from the combination of clinical presentation, endoscopy and biopsy findings, imaging, and other evidence. ASCA provides complementary information.
• Assay cutoffs are not transferable between laboratories, and this one is not transferable to gASCA.

Clinical Takeaway

This result comes in three tiers, and the middle one is not a mild positive — it is an unresolved test. Whichever tier you land in, read it with your companion ASCA IgA result; the pair adds context but does not settle a diagnosis. Bring the panel to your clinician as a set.

If you remember only one thing: equivocal is not a weak positive, and positive is not a diagnosis.

Bottom line. ASCA IgG is an adjunct to a diagnosis made elsewhere. It can support a picture, it can weaken one, and it can fail to resolve — but it does not settle anything by itself.

This page is not medical advice. Assay cutoffs differ between laboratories, and only your own clinician can interpret your result in the context of your history, symptoms, and other findings.