Whose instructions should I follow?

The ones from the lab running your test, without substituting anything you read elsewhere. Because the protocols differ, following a set of instructions from a different provider can invalidate your test while feeling like diligence. If your kit did not come with instructions, that is worth a phone call before you use it.

What happens if I get the preparation wrong?

Usually nothing visible. That is the problem. A preparation failure does not flag itself on the report, so it returns a number that looks like every other number. If you know you deviated, saying so is more useful than hoping it did not matter.

Can I prepare for a test I bought without a clinician?

You can follow the instructions, but nobody is checking your circumstances against them first. Direct access removes the step where someone asks whether anything you are taking or anything about your situation interacts with the preparation, and that step is doing real work.

Preparing for a breath test

By BeatSIBO editorial team · Updated August 7, 2026

The preparation is not an administrative formality attached to the real test. It is part of the measurement.

Why this page cannot give you a protocol

The short answer

Every provider publishes its own preparation instructions and they do not agree with each other. Publishing one set here would mean handing some readers rules that contradict the lab actually running their test. Follow the instructions that came with your test, from the provider running it, and treat anything else you read as information about a different test.

That includes this page. What we can usefully do is explain what the preparation is trying to achieve and why deviations matter, so the instructions you were given make sense rather than reading as arbitrary.

What the preparation is actually for

The test measures gases produced when bacteria ferment a sugar you drink. For that measurement to mean anything, the gas has to come from the sugar you were given rather than from whatever else happened to be fermenting. Most of what preparation asks of you serves that one purpose: reduce the background so the signal is attributable.

Read that way, the instructions stop being a list of prohibitions and become a single idea applied several times.

The failure mode nobody warns you about

The short answer

A preparation failure does not produce an error. It produces a number. The report looks the same as a report from a correctly prepared test, and nothing on it records what you ate the day before or what you were taking that week. So the result arrives carrying a confidence it has not earned, and the only person who knows is you.

This is the practical reason to tell whoever ordered the test if you deviated, even if it feels like an admission. A result known to be unreliable is more useful than a result wrongly believed to be reliable, and it is much cheaper than acting on the second one.

Preparation is not why the tests disagree

It would be convenient if preparation explained the disagreement between test types, because preparation is something you can control. It does not.

Pimentel M et al., American Journal of Gastroenterology 2020 Clinical guideline

The guideline covering this area rates five of its six recommendations as resting on evidence its own authors grade as very low quality. The gap between two breath tests given to the same person is a fact about what the tests measure, not a sign that somebody prepared badly. Getting the preparation right removes one source of noise. It does not turn a contested measurement into a settled one.

What is not settled here

We are not able to tell you how much any specific deviation moves any specific result. As far as we can find, that has not been quantified in a way that would let anyone answer it honestly, and a site that gives you a confident number for it is telling you something it does not know. What is clear is the direction of the problem: deviations add noise to a measurement that is already noisy.

The question worth asking before you pay

Ask which substrate the test uses, how long the collection window runs, and what the preparation requires. All three change what your result means, and all three are easier to ask about before the kit arrives than after you have a number you are trying to interpret.

Common questions

Whose instructions should I follow?: The ones from the lab running your test, without substituting anything you read elsewhere. Because the protocols differ, following a set of instructions from a different provider can invalidate your test while feeling like diligence. If your kit did not come with instructions, that is worth a phone call before you use it.
What happens if I get the preparation wrong?: Usually nothing visible. That is the problem. A preparation failure does not flag itself on the report, so it returns a number that looks like every other number. If you know you deviated, saying so is more useful than hoping it did not matter.
Can I prepare for a test I bought without a clinician?: You can follow the instructions, but nobody is checking your circumstances against them first. Direct access removes the step where someone asks whether anything you are taking or anything about your situation interacts with the preparation, and that step is doing real work.