Understanding Your Lab Results: IgA, Tryptase, and MCAS
Why a normal tryptase does not rule out Mast Cell Activation Syndrome — and why IgA is a separate question
Yoon Hang Kim, MD, MPH | Board-Certified in Preventive Medicine | Integrative & Functional Medicine Physician
If your recent lab work showed an elevated IgA level and a normal tryptase, you may be wondering what this means for the question of Mast Cell Activation Syndrome (MCAS). Here is the short answer: neither result rules MCAS in or out. MCAS is a diagnosis made by combining your clinical story with a very specific kind of biochemical evidence — a documented, event-related rise in tryptase — not by a single resting lab value, and not by IgA at all. Let me walk you through why.
How MCAS Is Actually Diagnosed
The internationally accepted consensus criteria (first published in 2012 and reaffirmed through 2024) require all three of the following:
- Typical symptoms. Recurrent, episodic symptoms involving two or more organ systems — for example skin flushing or hives, gut cramping or diarrhea, low blood pressure, wheezing, or full anaphylaxis.
- Biochemical proof of a mast cell event. A substantial rise in serum tryptase during a symptomatic episode, using the “20% + 2” formula: the acute level must exceed your own baseline × 1.2, plus 2 ng/mL.
- Response to treatment. Meaningful improvement with mast-cell–directed therapy (such as antihistamines and mediator-blocking medications).
Why a Normal Tryptase Does Not Exclude MCAS
The key word in the criteria above is rise. The diagnostic marker is the change over your own baseline — not the absolute number. A baseline tryptase anywhere in the normal range (roughly 1–11 ng/mL) is fully compatible with MCAS. In fact, national guidelines note that in mast cell disease, tryptase may stay under 20 ng/mL or be only transiently elevated.
Demonstrating that rise requires a paired tryptase:
- An acute sample, drawn during a symptomatic episode — ideally about 30 minutes to 2 hours after symptoms begin, and up to 4–6 hours afterward.
- A true baseline sample, drawn at least 24 hours after all symptoms have fully resolved.
So if the only tryptase you have ever had drawn was taken while you were feeling well — or was never paired with an episode — the biochemical criterion simply hasn’t been tested yet. A normal isolated tryptase means the question remains open. It does not confirm MCAS, and it does not refute it.
Where Does the Elevated IgA Fit In?
It doesn’t — at least not for MCAS. Serum IgA is not part of any MCAS diagnostic criterion. The accepted mast cell mediators are tryptase (the preferred marker) and, less specifically, histamine metabolites, prostaglandin D2 metabolites (11β-PGF2α), and leukotriene E4 measured in urine or blood.
An elevated IgA neither supports nor excludes MCAS. It does deserve its own follow-up, because it can reflect unrelated processes such as recent or chronic infection, inflammation, chronic liver disease, or — less commonly — a monoclonal gammopathy (an IgA paraprotein). We will evaluate it on its own track.
What We Do Next
- Capture a paired tryptase. The single most useful step: draw tryptase during your next significant episode, then repeat it once you are back to baseline, and apply the 20% + 2 formula.
- Consider alternative mediators. If tryptase is repeatedly non-diagnostic, we can check 24-hour urinary N-methylhistamine, 11β-PGF2α, and leukotriene E4.
- Screen for conditions that change the interpretation. A persistently elevated baseline tryptase (in the ~8–20 ng/mL range or above) should prompt evaluation for hereditary alpha-tryptasemia (TPSAB1 gene copy number) and for clonal mast cell disease or systemic mastocytosis (KIT D816V testing, REMA score, and — when indicated — bone marrow biopsy).
- Work up the IgA separately. We will look for the common, unrelated explanations rather than folding it into the MCAS question. For functional medicine evaluation, I use Infinite Labs Food Allergy testing which looks at IgE, IgG, IgG4, and C3 which is the most comprehensive testing.
In health,
Yoon Hang Kim, MD, MPH
Important: This handout is for educational purposes and reflects your individual care discussion. It is not a substitute for medical evaluation. If you experience symptoms of anaphylaxis — throat tightness, difficulty breathing, fainting, or widespread hives with dizziness — use your epinephrine auto-injector if prescribed and call 911 immediately.
Professional: www.yoonhangkim.com | Clinical: www.directintegrativecare.com
