When it comes to assessing if a patient has Intestinal Hyper-Permeability, or Intestinal Barrier Penetration, a.k.a. “Leaky Gut“, there are currently only a handful of reliable lab tests that are used. It is helpful to assess and establish a baseline of Leaky Gut with laboratory testing in order to determine treatment efficacy, direction and duration.
Functional Medicine practitioners are trained to look at physiology from a different perspective. We look beyond the constellation of symptoms in order to analyze the underlying root cause of a person’s current physiologic state.
Leaky Gut Pathways:
- Paracellular Pathway: between the cells, through the “tight junctions”
- Transcellular Pathway: through the specialized cells that line the gut, called enterocytes.
Increased permeability of the intestinal barrier to macromolecules is associated with a variety of inflammatory conditions. Intestinal hyper-permeability can cause systemic inflammation, leading to various clinical conditions including:
- Food Allergies, Food Sensitivities
- Gluten Sensitivity and Celiac Disease
- Inflammatory Bowel Disease (Crohn’s disease, Ulcerative Colitis)
- AutoImmune Diseases (Rheumatoid Arthritis, Psoriasis, Type 1 Diabetes, Spondylitis, etc.)
- Cognitive Dysfunction (Anxiety, Depression, Schizophrenia, etc.)
- Neurological Conditions (Guillian Barre Syndrome, Multiple Sclerosis, etc.)
3 Common “Leaky Gut” Lab Tests
- Lactulose / Mannitol Testing (urine)
- Occludin, Zonulin, Actomyosin Protein Antibody Testing (serum-blood draw)
- Zonulin Levels (serum-blood draw)
(1) Lactulose / Mannitol Testing (urine)
This lab test has been used for over 40 years, and measures the ability of two sugar molecules, lactulose and mannitol, to permeate through the intestinal epithelial barrier (a.k.a. “The Brush Border”). Mannitol is a small sugar molecule that is easily absorbed, whereas Lactulose is a larger molecule and is not readily absorbed. After a baseline urine sample is collected, the patient ingests the sugary Lactulose and Mannitol solution and a six-hour timed urine collection follows. 
PROS of Lactulose / Mannitol Testing
- Affordable (under $50)
- Easy to perform: at home, urine sample
CONS of Lactulose / Mannitol Testing
- Can exacerbate symptoms associated with SIBO (Small Intestine Bacterial Overgrowth)
- Measures permeability of small sugar molecules (342 Da in size): these sugars are not antigenic, and therefore do not challenge the immune system.
- The problem with Lactulose/Mannitol testing is that it lacks the ability to analyze antigenic macromolecule passage. Antigenic macromolecules that penetrate through the epithelial barrier can trigger the immune system, causing and exacerbating underlying inflammatory conditions, and autoimmune disease. 
- Lactulose has relatively low molecular size, and the transfer of this substance through the gut barrier is not reflective of the transfer of food proteins and overall immune response.
Labs that offer Lactulose / Mannitol Testing
- Genova Diagnostics: “Intestinal Permeability Assessment”
- Doctor’s Data Labs: “Intestinal Permeability Test”
(2) LPS, Occludin, Zonulin, Actomyosin Protein Antibody Testing (serum- blood draw)
Many advances and discoveries have been made over the last two decades in the world of Immunology. Where the Lactulose/Mannitol test measures the transfer of small molecules only through the paracellular pathway, it is more helpful to assess both the paracellular and the transcellular pathways.
Using a Large Molecule Intestinal Permeability Identification (LMIPI) allows the assessment of large molecules comparable to the size of food proteins, which are antigenic and challenge the immune system.
Lipopolysaccharides (LPS) are large molecules found in gram-negative bacteria. They are endotoxins, and if/when absorbed, elicit a strong immune response. The detection of antibodies against LPS indicates macromolecule-sized endotoxin infiltration through the intestinal barrier into the systemic circulation.
Occludin is a major component of the proteins holding together the tight junctions. The detection of antibodies against occluding indicates that the tight junctions are breaking down (paracellular pathway).
Zonulin is a protein that regulates the permeability of the intestines.  The detection of antibodies against zonulin indicates that the normal regulation of the tight junctions is compromised (paracellular pathway).
The Actomyosin Network is a protein complex that regulates intestinal barrier function by maintaining the plasticity of tight junctions. Antibodies to the actomyosin network are a biomarker of intestinal barrier dysregulation via cell infiltration (transcellular pathway).
PROS of LPS, Occludin, Zonulin, Actomyosin Protein Antibody Testing
- Easy to identify level of Leaky Gut (transcellular vs paracellular) and Cause (LPS- bacterial overgrowth vs Stress vs Food sensitivities).
- Large Molecule intestinal Permeability Identification (LMIPI) assesses large molecules comparable to the size of food proteins, which are antigenic and challenge the immune system.
- Clearer look at intestinal immune system dysregulation, and defective oral tolerance by analyzing LMIPI. Generally, the larger the molecule, the less likely it is to have access to systemic circulation.
CONS of LPS, Occludin, Zonulin, Actomyosin Protein Antibody Testing
- Antibody measurement is influenced and suppressed by the use of Steroids. The patient has to have been off of oral and topical steroids for approximately 60 days prior to testing.
- The lab levels available currently are based off of Adults only. This makes it challenging when assessing the Pediatric population. While a positive is definitively a positive Antibody reaction, it is possible to get a false negative in Peds due to lack of pediatric normal ranges.
Labs that offer Occludin, Zonulin, Actomyosin Protein Antibody Testing
- Cyrex Laboratories: “Array 2- Intestinal Antigenic Permeability Screen”
(3) Direct zonulin measurement (serum- blood draw)
Circulating Zonulin is a clinically useful marker of intestinal permeability, or gut wall integrity.  High levels of zonulin have been associated with increased intestinal permeability, as zonulin induces the breakdown of tight junctions between intestinal epithelial cells.
PROS of Zonulin Measurement
- Direct Measurement of zonulin (vs Antibody expression to Zonulin) will not show false negative with the use of oral or topical Steroids. However, see the first Con below.
CONS of Zonulin Measurement
- Zonulin levels may increase with corticosteroid use: showing potential false positives for Intestinal permeability.
- Zonulin levels can be higher in obese patients, and glucose intolerance: showing potential false positives for Intestinal permeability.
- Cost of testing is about the same price range as the Cyrex Array 2 (which offers a more in depth look at Intestinal Permeability).
Labs that offer Zonulin Measurement
Depending on the Functional Practitioner you are working with, they may use different labs based off of their own clinical preferences. You can see the Pros and Cons to each lab above.
As for my own personal preference: if a patient has not recently used any corticosteroids or immunosuppressant drugs, I will typically start with Cyrex Labs Array 2 (Intestinal Antigenic Permeability Screen). If they have been using corticosteroids, I will run a direct Zonulin measurement, or wait 30-60 days until they have gone off of their corticosteroid and then test Cyrex Labs Array 2.
Clinically I have been using Cyrex Labs since they opened in January 2011, and have currently ordered approximately 3,000 labs through Cyrex Labs (which is kind of wild to think about!).
So what do you do now?
Head on over to these other awesome articles!
STEP #1: Assess whether you have Leaky Gut
- Understand this Article: Lab Testing PROS & CONS for Leaky Gut / Intestinal Permeability
- Read: What Exactly is this Leaky Gut Phenomena?
STEP #2: Determine the Cause/s of Leaky Gut
- Article: 6 Common Causes of Leaky Gut
STEP #3: Remove the cause/s of Leaky Gut, while also repairing the gut barrier (brush border)
A Functional Medicine Practitioner can help guide you along all of these steps. It is in your best interest to work directly with a practitioner who has experience analyzing, assessing and treating Leaky Gut as well as your overall symptoms.
I hope you enjoy this “Inspired Lab Testing Tip” for Leaky Gut!
Dr. Meaghan Dishman
©2016 Dr. Meaghan Dishman ND, LAc, MSOM