So, you’ve been diagnosed with a digestive condition such as irritable bowel syndrome, cut out gluten and any trigger foods, and still have symptoms. The next step should be to get tested for small intestinal bacterial overgrowth (SIBO). If you are not sure what to ask for, read below for information on the most common testing used to diagnose SIBO.

Breath testing

Breath testing is the most common and least expensive form of testing for SIBO. This type of testing helps detect the presence of any methane or hydrogen, which are gases that the body itself cannot produce. If colonic-type bacteria are present, then when carbohydrates are broken down in the gut, hydrogen and methane concentrations in the breath will change. Such testing will usually proceed as follows:

• Lactulose and glucose are used as substrates. You will be given these substrates as part of the testing.
• Prior to testing, patients must be off any antibiotics for two weeks, avoid high fiber foods the day before, and fast for 12 hours before the testing.
• Results will vary based on the types and proportions of colonizing bacteria, residual carbohydrates, as well as the patient age and sex. However, there is an objective diagnostic threshold that will help determine if someone is living with SIBO.

Since this type of testing can have high false-positive rates, it is not the gold standard for SIBO testing, but can be a useful tool to start with in the diagnostic process.

Small-bowel testing

Small-bowel jejunal aspiration and culture is the most widely accepted test of choice for diagnosing SIBO. This type of testing involves looking for bacterial growth in the small intestine from small-bowel aspirate, or matter extracted from the bowel usually through an endoscopy. This type of test involves a tube with a small camera attached to it that will be used to travel through your digestive tract and look for any abnormalities. In SIBO testing, an upper endoscopy would likely be used, which means that the doctor will want to look at the upper part of your digestive system to obtain the small-bowel sample. Testing preparation will proceed as follows:

• Stop eating or drinking four to eight hours before the procedure, or as recommended by your doctor. This is to ensure that your stomach is empty for the procedure.
• Stop taking certain medications, such as blood thinners, before the procedure as recommended by the doctor.
• During the testing, monitors will often be attached to your body so that your vitals such as blood pressure and breathing can be monitored during the procedure.
• You will likely be given a sedative to help you relax during the procedure.
• An anesthetic will be sprayed in your mouth to numb your throat so that the doctor can place the tube down your throat for the testing without you feeling any discomfort. A mouth guard may also be placed in your mouth.
• Once the tube is placed in your throat, it will travel down your esophagus and into your digestive tract to look for any abnormalities. Once the tube reaches the duodenum in your small bowel, the doctor will use special tools attached to the tube to extract the culture sample.

This type of testing usually takes about 15 to 30 minutes, and afterwards you will be asked to take it easy and rest for the remainder of the day. You may experience some post-procedure symptoms as sore throat, bloating and gas (from the air blown into the digestive tract to help the tube move freely), and/or cramping. These symptoms should subside throughout the day.

The diagnostic threshold for this culture test is between 10³ colony-forming units per milliliter to 10⁵ colony-forming units per milliliter. Although, false positives may occur due to contamination of the culture from bacteria in the mouth or esophagus, or false negatives may occur if the tube cannot fully reach the small bowel.             

Antibiotic therapy

A therapeutic trial of antibiotics is another way to help determine if someone has SIBO. This type of testing involves the patient taking different antibiotics to see if treatment is accepted or not. If it is not working, then a diagnosis of SIBO is not ruled out. This type of testing can be concerning though since using antibiotic use with those displaying nonspecific symptoms may lead to antibiotic resistance. Also, unwanted side effects may occur, and potentially a patient could develop C. difficile colitis from antibiotic treatment, which is an infection that can cause diarrhea and belly pain. This type of testing is also concerning since there is no criteria set in place as to a diagnostic result.

So, what testing should I get done?

The type of testing you receive will depend on your particular symptoms and medical history.  Your doctor will recommend what type of testing they feel would be best. However, research is hoping that upon further study, the breath testing can be improved in its specificity.  This is because this test is the least invasive, most accessible, and least expensive, so that those with digestive symptoms can be diagnosed more easily and in turn receive the appropriate treatment and relief from symptoms.

Written by Staci Gulbin, MS, RD a Board-certified dietitian.