Fecal lactoferrin is a protein found in stool that serves as a common diagnostic marker in gastroenterology. This substance is released into the digestive tract when the lining of the intestines is inflamed. Measuring its concentration provides a non-invasive way to assess active inflammation within the gastrointestinal system. The test is often used to help determine the underlying cause of persistent abdominal symptoms like chronic diarrhea and pain. This simple stool test guides medical decisions, helping determine whether more invasive procedures are necessary for a complete diagnosis.
Understanding Lactoferrin
Lactoferrin is a glycoprotein that plays an important part in the body’s innate immune system. This protein is produced primarily by neutrophils, a type of white blood cell that rushes to the site of injury or infection. It is naturally found in various bodily secretions, including human milk, tears, and saliva, where it acts as a first line of defense against pathogens.
One of lactoferrin’s core functions is its ability to bind tightly to iron. By sequestering iron, it limits nutrient availability for harmful bacteria, which require iron to grow and multiply, exerting an antimicrobial effect. When inflammation occurs in the intestinal lining, neutrophils migrate from the bloodstream into the gut tissue. As these immune cells die, they release lactoferrin into the intestinal lumen, which is then excreted in the stool.
The concentration of lactoferrin in a stool sample is a direct reflection of the number of active neutrophils present in the digestive tract. Because the protein is stable and resistant to degradation by digestive enzymes, it provides a reliable, measurable marker of active inflammation. This stability is an advantage over testing for white blood cells themselves, which quickly degrade after excretion.
The Clinical Purpose of the Fecal Lactoferrin Test
Physicians primarily order the fecal lactoferrin test to help differentiate between two major categories of gastrointestinal disorders: organic disease and functional disorders. Organic diseases, such as Inflammatory Bowel Disease (IBD), cause measurable physical inflammation and damage to the intestinal lining. Functional disorders, like Irritable Bowel Syndrome (IBS), cause symptoms like pain and altered bowel habits but do not involve physical inflammation or structural damage.
The test serves as a sensitive screening tool to detect active intestinal inflammation. A positive result suggests an inflammatory condition, while a negative result effectively rules out significant active inflammation in most cases. This distinction directs the diagnostic pathway, reducing the need for invasive procedures like colonoscopy in patients whose symptoms are likely due to a non-inflammatory cause.
For patients already diagnosed with IBD, which includes Crohn’s Disease and Ulcerative Colitis, the test is used to monitor disease activity. Measuring lactoferrin levels over time helps determine if the disease is flaring up or if the patient is in remission. A rising concentration of fecal lactoferrin can indicate a pending relapse, sometimes even before the patient experiences a return of severe symptoms.
What Test Results Indicate
The results of a fecal lactoferrin test are typically reported as a concentration, often in micrograms per gram of stool (µg/g). A low or negative result, generally below a cutoff of approximately 7.25 µg/g, suggests the absence of significant active inflammation in the gut. These low levels are commonly found in healthy individuals and in those with functional gastrointestinal disorders, such as IBS.
Moderately or highly elevated results indicate active inflammation is present in the intestines. The concentration often correlates with the severity of the inflammation, meaning higher levels are seen in more severe cases. Specific conditions associated with these elevated levels include IBD (Crohn’s Disease and Ulcerative Colitis), infectious colitis caused by certain bacteria, and severe Clostridium difficile infection.
An elevated fecal lactoferrin level does not identify the precise cause or location of the inflammation, but it signals the need for further evaluation. A high result often prompts a physician to refer the patient for additional diagnostic testing, such as an endoscopy or colonoscopy, to visually inspect the intestinal lining and obtain tissue samples for a definitive diagnosis. Conversely, a result below the established threshold suggests that a non-inflammatory condition is the more probable cause of the symptoms.