Lactose Intolerance Screening (Qualitative Fecal Hydrogen Gas)

This test gives your care team important information about your health that a physical exam alone cannot provide. It can help confirm or rule out a condition, guide decisions about your treatment, and sometimes find problems early, when they are often easier to treat and manage.

Lactose intolerance is common and often linked to digestive symptoms after consuming dairy. This test helps identify whether your body produces insufficient lactase, the enzyme needed to break down lactose. If confirmed, dietary adjustments may help relieve symptoms like bloating, gas, or diarrhea.

Before your test, your provider will explain how to prepare, and you may be asked to avoid certain foods, drinks, or medicines for a short time. Follow the instructions you are given closely, plan to arrive a little early, and bring a list of your current medications along with any questions you want to ask.

You’ll be asked to avoid dairy products (including milk, cheese, yogurt, and ice cream) for at least 48 hours before testing. You may also be instructed to eat a low-lactose diet for a few days beforehand. Bring a list of foods you eat to discuss with your healthcare provider.

During the test, a trained member of your care team will explain each step and tell you what to expect. Depending on the type of test, you may be asked to sit still, lie down, or hold a certain position for a short time. Most tests are quick, cause little or no discomfort, and you can ask questions at any point.

A small sample of your stool is collected, usually via a stool collection kit provided by your lab. The sample is then analyzed to detect hydrogen gas produced by gut bacteria breaking down undigested lactose. The test is non-invasive and typically done in a doctor’s office or at home.

Your results show whether your values fall within the expected range. Readings outside that range do not always mean something serious is wrong, and your provider will consider them together with your symptoms, medical history, and other test results. Be sure to review your results with your provider and ask about any follow-up steps.

If your results show elevated hydrogen levels (above normal limits), it suggests lactose intolerance. However, results alone may not confirm the diagnosis—symptoms and dietary history are also considered. A positive test may guide dietary changes or further testing if needed.