Lactose intolerance breath test

For symptoms such as diarrhoea, nausea, bloating, gas and abdominal cramps, this test can provide information on whether you have an intolerance to sugars such as lactose.

ALL TEST ARE ACCREDITED & REGULATED BY

What is a lactose intolerance breath test?

This simple carbohydrate intolerance breath tests can provide information on whether you have an intolerance to sugars such as lactose or fructose.

You may be referred for a test if you are experiencing symptoms including diarrhoea, nausea, bloating, gas and abdominal cramps as many of these symptoms can be attributed to digesting foods with certain sugars and carbohydrates.

A lactose intolerance breath test can help to uncover malabsorption of lactose (the sugar in dairy).

SIBO (Small Intestinal Bacterial Overgrowth) can cause a false positive result on these tests, so we always recommend to rule out SIBO with a SIBO breath test before taking an intolerance test.

How it works

You will provide an initial breath sample by blowing into a test tube through a straw, or into a breath collection bag. This will give us your baseline reading.

You will drink water with lactose over 1–2 minutes. Breath samples will be taken every 40 minutes for 3 hours and 20 minutes to monitor how your body processes the carbohydrate.

Along with the samples, you will record any symptoms experienced using the symptom form provided in order for your clinician to have a comprehensive overview of data and symptoms to analyse.

Download the information leaflet

Preparing for your test

Before you test, there are some things we ask you to do, to ensure safety and accurate results. This includes stopping certain medication and fasting for a short period.

Please read our patient information leaflet for full details.

For 4 weeks before your test

Do not take any antibiotics

For 1 week before your test

Do not take laxatives or stool softeners Movicol, Dulcolax, Ex-Lax, Senna, Milk of Magnesia etc.

Do not take stool bulking agents Metamucil, citrucel etc.

Do not take motility agents Prucalopride, linaclotide etc.

Do not take probiotics

VSL#3, Actimel, Yakult etc

  • You can continue taking any other essential medicines.

ⓘ Additionally, there must be a period of one week between any tests which require cleansing of the bowel e.g. colonoscopy, barium enema, before having a breath test.

For 2 days before your test

No anti-diarrhoeal medication (e.g. Loperamide (Imodium))

The day before your test

  • • Plain white bread

    • Plain white rice

    • White potatoes (no skin)

    • Baked/grilled chicken, turkey, lean beef, lean pork, white fish (no oily fish)

    • Maximum of 2 eggs

    • Water (non-carbonated)

    • Non-flavoured black coffee (no milk)

    • Non-flavoured black tea (no milk and no herbal teas)

    • 1 tbsp butter/margarine/oil

    • Salt to flavour food

Do not eat or drink anything else, eating prohibited foods could give false results for the test.

ⓘ If you are diabetic requiring insulin or diabetes medicine, please ask your doctor if you should change your morning dose. Oral hypoglycaemic medicines are usually not taken that morning until completion of the test and you start eating again.

For 12 hours before your test

You must stop eating and drinking and fast for 12 hours before your test.

The day of your test

You may take your essential medicines with a small amount of water but make sure you do not take anything that may affect your bowel (see previous list).

You may brush your teeth, but please try not to swallow any toothpaste.

Do not eat, drink, chew gum, smoke, eat breath mints and/or other sweets on the morning of or during of your test.

If you are diabetic requiring insulin or diabetes medicine, please ask your doctor if you should change your morning dose. Oral hypoglycaemic medicines are usually not taken that morning until completion of the test and you start eating again.

Getting your test results

The results will be displayed as a graph that can be analysed by our clinical team to see if have an intolerance to sugars such as lactose.

Your data will be analysed and results written up into a report. The report will be sent to both you and your referring consultant/doctor, who will explain the results to you in a follow-up consultation and find the next step for managing your symptoms.

Paying for your test

Self-paying: If you are paying for this test yourself and not through insurance, the cost will be £250.

This cost includes the breath test, analysis and report.

Insurance coverage

If you have private medical insurance, most companies can cover this for you.

Got a question or want to find out more about our tests?

© Copyright The Functional Gut Group 2025