How do I take a SIBO breath test?

Need to know how to take a SIBO breath test? We’ve got you covered.

Taking a SIBO breath test is straightforward and, with a little preparation, you’ll be able to complete the test smoothly. We’ll walk you through everything from activating your kit and preparing your diet, to taking your samples and posting them back to our lab.

Read the instructions

Even if you’ve done a breath test before, take time to read the instructions included with your kit. The process may have changed since your last test and it’s important to understand exactly what’s involved. Your instruction leaflet will also list all the items that should be in your kit, so check that everything is there.

We’ve also made a quick video to guide you through the process:

How the SIBO breath test works

The SIBO breath test measures the gasses produced by bacteria in your small intestine.

You’ll first take a baseline breath sample on an empty stomach. Then you’ll drink a sugar solution called lactulose, which isn’t absorbed by the body but is metabolised by bacteria to produce hydrogen and methane gas.

You'll then take a series of breath samples over time. The higher the gas levels in the samples, the more bacteria are present and the more likely you are to have SIBO.

Timings

The SIBO breath test takes around 2.5 hours. Plan ahead and make sure you have a quiet morning set aside.

• Take the test in the morning on a Monday, Tuesday or Wednesday.
• You’ll need to fast for 12 hours overnight before starting (water only).
• Allow plenty of time to complete the test and return it in the post same day.
• Post your kit back as soon as you can so the samples arrive promptly at the lab. Avoid weekends and Bank Holidays.

Prepare yourself

Diet in the run-up to your test

Certain foods, drinks, and medications can affect your results. Follow these rules carefully:

• 4 weeks before: no antibiotics or antimicrobials.
• 2 weeks before: no laxatives or antacids (such as Rennie, Gaviscon).
• 2 days before: avoid sugar, probiotics, prebiotics, and alcohol.
• 1 day before: avoid dietary fibre (fruits, vegetables, whole grains, legumes, nuts, seeds, dairy). Stick to plain, low-fibre foods like white rice, chicken or fish, and eggs.
• 12 hours before: fast overnight — water only. Don’t use toothpaste or mouthwash (rinse with water only). No chewing gum.

On the morning of your test

• Don’t smoke for an hour before your test.
• Avoid physical activity.
• Don’t go back to sleep after waking up.

Activate your test kit

Before you start, activate your kit using the Selph dashboard and the Kit ID on your request form. This links your samples to your details in the lab. If you forget to activate, your results can’t be processed.

Prepare your space

Choose a clean, flat surface to set up your kit. Lay out:

• Your labelled tubes in order (1–7).
• The breath sampling device.
• The lactulose sachet.
• The request form and prepaid return envelope.

Make sure each tube is labelled with your name, date of birth, and today’s date. Arrange them in order so they’re easy to use.

Taking your breath samples

You'll use the breath sampling device and special vacuum tubes to collect your samples. You'll fill the gas bag by breathing into it and then attach a vacuum tube to the bag which will suck in your breath.

1. First sample: Start by taking your baseline breath sample using tube 1 (white).

• Inhale, hold your breath for 5 seconds, then exhale steadily through the sampling device. Inserting tube 1 into the holder for a few seconds to collect the sample.
• Write the time on the tube and form, then place the tube into the protective pouch.

2. Drink the lactulose: Empty the sachet into a glass or drink directly from it. You can have a small glass of water afterwards if needed. Note the time — this is “time zero.”

3. Subsequent samples: Take the next samples at the timings below:

• Tube 2 (green): 30 minutes
• Tube 3 (blue): 50 minutes
• Tube 4 (pink): 70 minutes
• Tube 5 (black): 90 minutes
• Tube 6 (yellow): 120 minutes
• Tube 7 (purple): 150 minutes

Record the time of each sample on your form and tube.

Important tips:

• Don’t open tubes before use (they are vacuum sealed).
• Don’t put your finger inside the collection tube (there’s a needle inside).
• Stay relaxed and seated while taking your samples.

Fill in your details

Double-check that:

• All tubes are labelled correctly.
• Your request form is complete.

This ensures the lab can match your samples to your results.

Post your SIBO breath test to the lab

Put your tubes, breath sampling device and request form back into the kit box. Place the box inside the prepaid return envelope and take it directly to a post office the same day.

We’ll notify you once your kit arrives at the lab. Because the samples are processed in Europe, delivery can take a couple of days.

When will you receive your SIBO breath test results?

Results are usually ready within 14 working days (often much sooner). As soon as your results are available, you’ll get an email and can view your report in your Selph dashboard. One of our doctors will explain your results and what they mean for your gut health.

Can I order a SIBO breath test today?

You can order a SIBO breath test from Selph. We’re here to help you get answers about your gut health and support you with expert advice. Order your SIBO breath test today.