Clinical Practice

Allergy, Sensitivity, Tolerance: Three Words That Shape Three Different Plans

Patients use allergy, sensitivity and tolerance interchangeably. Clinically they point to different mechanisms, different markers and different treatment plans. Here is how to keep them separate.

When a patient tells you they are allergic to dairy, you are hearing a conclusion, not a finding. Sometimes it means their throat tightens within minutes. More often it means they feel heavy and foggy a few hours after a latte, or that a previous practitioner told them to cut it out and they never went back. Those are three different clinical situations with three different plans, and the word the patient reaches for does not distinguish between them.

Getting the vocabulary straight early is one of the more useful things you can do in a first consultation. It sets expectations, it shapes what you test for, and it determines whether the eventual plan is lifelong avoidance or a structured trial with a route back.

Three Words, Three Clinical Questions

**Allergy** in the clinical sense refers to an immediate, IgE-mediated reaction. Onset is fast, the dose can be small, and the stakes can be high. This is the category where avoidance is not negotiable and where the conversation includes emergency planning rather than reintroduction.

**Sensitivity** describes delayed reactions, where symptoms surface hours or days after exposure and the link back to the food is much harder for a patient to see on their own. IgG and IgG4 markers sit in this space. The relationship between antibody levels and symptoms is not one to one, which is exactly why the clinician's judgement matters more here than anywhere else on the panel.

**Tolerance** is the question of how much, how often, and in what combination. A patient may handle a food comfortably in isolation and poorly when it arrives alongside three others that are also elevated, or during a period of high stress and poor sleep. Tolerance is not a fixed property of the food. It is a property of the patient at a moment in time.

Why the Distinction Changes the Plan

If you treat a delayed sensitivity like an allergy, you end up with a permanently narrowed diet and a patient who has lost foods they may not have needed to lose. Long-term restriction has its own costs: nutritional gaps, social friction, and a growing anxiety about eating that outlasts the original complaint.

If you treat an allergy like a sensitivity, the error runs the other way and is more serious.

And if you ignore tolerance entirely, you get the pattern most clinicians will recognise: a patient who does well on a strict protocol, reintroduces everything at once because the list felt arbitrary, reacts, and concludes the whole exercise was pointless.

The Load Question

Tolerance is also where complement belongs in the conversation. Complement activation, measured through C3b/d, speaks to amplification — the same exposure producing a much larger inflammatory response. Intelligent Solutions DX's published material notes that complement can amplify a reaction substantially, which gives you a mechanism to explain to a patient why one week they get away with something and the next week they do not.

That framing is useful because it moves the discussion away from good foods and bad foods and toward cumulative load. Patients tend to find it more credible, and it makes the reintroduction phase easier to justify.

Having the Conversation

Most of the presentations that lead a patient toward this line of enquiry are non-specific: fatigue that does not resolve with sleep, bloating and irregularity, joint stiffness, skin flares, headaches with no clear trigger. NIH studies indicate at least 20 percent of the American population have food sensitivities, so the base rate is not trivial, but neither is it a reason to attribute every vague symptom to diet.

What works is honest framing. You are looking at immune markers linked to specific foods. The markers inform your thinking; they do not hand down a verdict. The plan that follows will be a structured trial, and the patient's reported response during that trial is part of the evidence.

Where This Lands in Different Practices

The same distinction plays out differently depending on the setting:

• Clinics running general practice can triage which patients need urgent allergy pathways and which are candidates for a slower sensitivity and tolerance investigation.
• Dietitians building virtual services have a defensible structure for a multi-session engagement rather than a single consultation.
• Chiropractors working with inflammatory presentations get a dietary variable to examine alongside mechanical findings.
• Union members with covered access face no cost barrier, which removes the usual reason a patient defers testing.

IS382 COMPLETE covers 382 foods and measures IgE, IgG, IgG4 and complement C3b/d from an at-home serum collection. No equipment, no draw room, no additional chair time — the practice contributes the interpretation and the plan, which is the part that cannot be outsourced anyway.

The test gives you four different kinds of information. Keeping allergy, sensitivity and tolerance separate in your own head is what turns that information into a plan a patient can actually follow.