Understanding Digestive Lab Testing

If you suffer from diarrhea, constipation, abdominal pain, nausea or heartburn you know how much these symptoms can disrupt your life. What you may not know is that understanding the causes of these symptoms is important. There are many over-the-counter medications and home remedies for digestive symptoms, but simply covering them up isn’t a great long-term strategy. The symptoms may not improve on their own, or worse, masking them could delay diagnosing a more serious cause.

While your symptoms can give us a good idea of what’s going on, a lot of times we will want to run lab tests to confirm our suspicions, rule out more serious conditions, and monitor your therapy. In this article, we’ll discuss some of the common labs we run for digestive symptoms and related illnesses.

Food Sensitivities

  • Food sensitivities and food allergies are different. Food allergies cause immediate responses, which can be life-threatening in some cases. Food sensitivities, on the other hand, tend to have delayed effects that can result in digestive symptoms, or show up elsewhere in your body.

  • Food sensitivities are detected by taking a small blood sample and looking for antibodies to foods you commonly eat.

  • This test has some limits - false positives and false negatives do occur. Also, you can have a reaction to a food that this test cannot detect.


Comprehensive Functional Stool Testing

  • In the past, stool testing was notorious for missing positive results, but advances in the technology and the addition of other tests give us a better picture of what is happening in your digestion.

  • This kind of stool testing can differentiate if someone is experiencing IBS (irritable bowel syndrome) or IBD (inflammatory bowel disease). While the symptoms can look similar, IBD tends to be more serious in its consequences.

  • Markers for digestion and absorption are helpful in understanding whether someone is breaking down and absorbing their food properly.

  • We can also test for types and relative numbers of bacteria living in the digestive tract. This can give us a good idea if you have a diverse population of good bacteria, or if there are signs of overgrowth.

Blood Tests for Celiac Disease

  • Celiac Disease is an auto-immune condition where your body has an immune reaction triggered by eating gluten, a protein found in wheat and other grains. The condition can be difficult to definitively diagnose because it requires that you are still eating gluten and a biopsy to confirm it absolutely.

  • The testing for Celiac Disease is a panel of tests looking for several antibodies, and the results can sometimes be inconclusive. The test is helpful for determining who may benefit from eating a gluten-free diet.

  • Genetic testing combined with antibody testing has a good predictive value of who actually has Celiac Disease while avoiding an invasive biopsy.

  • In practice, many patients who test positive for antibodies on this panel will choose not to eat gluten, and not get a biopsy. In my experience, most of them improve from this.


SIBO Hydrogen and Methane Breath Testing

  • Small intestinal bacterial overgrowth (S.I.B.O.) symptoms can be non-specific such as abdominal pain, bloating, diarrhea, and flatulence.

  • This test is good for finding where your symptoms originate from in your digestive system (small intestine or large intestine).

  • This test involves drinking a known amount of sugar, then testing your breath at regular intervals to look for increases in hydrogen or methane gases.

  • If hydrogen or methane levels rise dramatically during the time when the sugar is in the small intestine it signals high levels of certain types of bacteria.


H. pylori Bacteria Testing

  • H. pylori is a type of bacteria that can live in your digestion and cause stomach ulcers, irritation to your digestive lining (gastritis), and contribute to stomach cancer.

  • H. pylori may also lead to some types of iron deficiencies, since it can block your absorption of iron from your food.

  • Multiple ways to test:

    • Stool - This is the least invasive and best way to monitor a current infection.If antibodies are found in your stool, it confirms you have an active infection. This testing can be done to follow up to make sure the bacteria is gone.

    • Blood - This testing just shows if you’ve been exposed to the bacteria, but cannot distinguish between a current or past infection.

    • Endoscopy - this involves a camera that goes into your stomach to take a sample (biopsy/culture). Although this is a good method, it is very invasive.

    • Breath - This involves drinking a solution of something called urea, and then taking a breath sample to measure carbon dioxide and ammonia. This does expose the patient to a very small amount of radiation.


Intestinal Permeability Assessment (Leaky Gut Testing)

  • This test can actually show us two important factors in your digestion: how much absorption is occurring in your digestion, and if you have increased intestinal permeability (leaky gut).

  • This test involves a drink with two types of sugars - one called mannitol, that is usually well absorbed, and one called lactulose that is usually poorly absorbed. After drinking it, you collect your urine to see how much of each of them is collected.

  • In a patient with normal absorption and no increased permeability, a high amount of mannitol and very small amount of lactulose will be collected in the urine. Abnormal values in either of these can indicate digestive problems that need to be addressed.


As you can see, each of these tests can give us different information about the causes of your symptoms. These are the most common tests we order for patients with digestive symptoms, or a medical condition where we suspect the gut is involved, but it is by no means an exhaustive list. Each patient’s case is unique, and these tests can prove incredibly useful for solving difficult to diagnose and difficult to treat cases. I’ve used these tests with great success in many patients who were unable to find help from other healthcare providers. Once we can determine what lab values are out of the normal range, we can use those labs to monitor the effectiveness of our therapy moving forward.