 A hydrogen breath test is performed to detect small intestinal bacterial overgrowth and also glucose or lactose malabsorption. Pre-testing Please avoid fiber supplements 24 hours before, antibiotics and antacids 4 weeks before, and prokinetics and anti-mortility drugs one week before the test. You must also be fasting for 12 hours. Please inform the doctor if you are diabetic. You will be given a hospital gown to change into and seated comfortably in a private area throughout. You are given glucose water before the test, which is performed using a small equipment called a gastrolizer. A disposable tube is attached to the gastrolizer and you need to breathe into it every 15 minutes for 2 hours. This is a painless procedure and takes about 2 hours. Your report will be issued in an hour post procedure.