Clinical labs streamline GI testing with MDx

The standard approach for determining the cause of diarrheal disease in a patient is tedious and time-consuming. The series of tests required for each case—representing a range of different assay types, each of which can take days to generate results—doesn’t serve the best interests of patients, physicians, or clinical labs, largely because they do not generate results quickly. The traditional approach was shaped by decades of adding tests for different bacteria, parasites, or other causes as the community’s understanding of these diseases expanded.

Surely if we could invent a new protocol from scratch, knowing everything we now know about these diseases and their causes, it would look nothing like the piecemeal, step-by-laborious-step approach currently used in labs. Today, with the rise of outcomes-based medicine, we have a rare opportunity to do exactly that: rethink how we manage testing for diarrheal diseases. Any effort to rein in costs while improving patient care must involve generating answers more promptly, subjecting patients to fewer tests, and accelerating decisions about treatment.

Molecular testing offers the streamlined process that could meet all of those requirements. There are several options available now, from panel tests that cover the vast majority of infectious causes of diarrheal diseases to “pick-and-choose” assays that allow physicians and lab experts to select the most likely agents. These diagnostics produce results rapidly, with higher accuracy and less hands-on time than conventional tests. They are cost-effective and, most importantly, they get actionable information into the hands of physicians so patients can be treated (or deliberately not treated) sooner.

This illustration depicts a three-dimensional (3D) computer-generated image of a cluster of drug-resistant, curly-cue shaped Campylobacter sp. bacteria. The artistic recreation was based upon scanning electron microscopic (SEM) imagery.

Diagnostic complexity

Diarrheal disease occurs frequently and has a remarkably high burden, leading to approximately 760,000 deaths in children under the age of five each year worldwide.1 Globally, there are an estimated 1.7 billion cases annually.

What makes these illnesses so difficult to diagnose is the vast array of potential causes and the tremendous overlap in symptoms. Diarrheal disease can be brought on by viruses, bacteria, and parasites, often through foodborne illness or unsanitary water. But there are also many non-infectious causes of diarrheal disease, such as medications, food allergies, and inflammatory bowel disease. Physicians trying to determine the cause of a patient’s diarrhea must become detectives, hunting for clues to help track down the culprit.

The process begins with a complicated flow chart, which recommends certain tests based on symptoms, travel history, duration of illness, and other pertinent factors. Those tests are run in various clinical labs; microbiology, virology, and molecular testing facilities are each responsible for certain assays. Tests that involve culturing are particularly time-intensive, requiring many different steps and a significant amount of hands-on time. Parasite tests require daily stool collection for three days followed by microscopy, which suffers low sensitivity because it is easy to miss the parasite by choosing the wrong bit of sample to examine.

Usually, these tests are run one at a time; with each negative result, the physician chooses another potential cause to test. Definitive results can take a week or more to generate, during which time the patient is likely either going without needed treatment or being given treatment that is not relevant to his or her specific condition.

Molecular testing

In recent years, new molecular tests have become available for various causes of diarrheal disease.2,3 These assays cover potentially responsible infectious agents—viral, bacterial, and parasitic—with some methods including more than 90 percent of potential culprits in a single panel. Other types of molecular tests allow users to select the most likely causes and test only for them, but if subsequent rounds of testing are needed, the existing sample can be used; it is not necessary to return to the patient to start the process all over again. Labs that have adopted molecular testing for diarrheal disease can eliminate the vast majority of culturing, enabling their staff to run tests for more patients in less time.

Some payers have expressed concern that panel-based molecular approaches constitute unnecessary testing because they assay for such a broad range of possible causes. The reality is that these tests dramatically improve patient care while reducing the time and costs associated with multiple rounds of conventional testing. Unlike the standard techniques, they produce useful diagnostic results for the vast majority of cases. For most patients, these tests replace a tedious, frustrating process with a “one and done” approach, in many cases getting them on the road to recovery faster. Molecular tests can simplify the diagnostic path for patients, physicians, and clinical labs teams alike.

Numerous studies of molecular tests for diarrheal disease have been conducted in patient populations around the world. Results from studies in Asia, Africa, the United States, and elsewhere consistently show that these assays are highly accurate, in some cases detecting pathogens missed by conventional tests that have long been considered the standard.4-7

They also detect cases of coinfection that would likely go undetected with a serial testing strategy. With such strong clinical utility, molecular testing offers the chance to streamline the diagnostic process for diarrheal disease, potentially reducing the morbidity and mortality burden associated with these illnesses.

Moving forward

As more clinical labs adopt molecular assays as the primary test for cases of diarrheal disease, we can expect definitive diagnoses for more patients, as well as shorter hospital stays. A significant reduction in the use of laborious conventional tests will also ease the burden on clinical labs, making it possible to generate answers for more patients in less time.


  1. Diarrhoeal Disease, Fact sheet N°330. World Health Organization.
  2. Dunbar S. Molecular revolution entering GI diagnostic testing. MLO. 2013;45(8):28.
  3. Binnicker MJ. Multiplex molecular panels for diagnosis of gastrointestinal infection: performance, result interpretation, and cost-effectiveness. J Clin Microbiol. 2015;53(12):3723-3728.
  4. Deng J, Luo X, et al. A comparison of Luminex xTAG® Gastrointestinal Pathogen Panel (xTAG GPP) and routine tests for the detection of enteropathogens circulating in Southern China. Diagn Microbiol Infect Dis. 2015;83(3):325-330.
  5. Duong VT, Phat VV, Tuyen HT, et al. Evaluation of Luminex xTAG Gastrointestinal Pathogen Panel Assay for detection of multiple diarrheal pathogens in fecal samples in Vietnam. J Clin Microbiol. 2016;54(4):1094-1100.
  6. Gu Z, Zhu H, Rodriguez A, et al. Comparative evaluation of broad-panel PCR assays for the detection of gastrointestinal pathogens in pediatric oncology patients.
    J Mol Diagn. 2015;17(6):715-721.
  7. Albert MJ, Rotimi VO, Iqbal J, Chehadeh W. Evaluation of the xTAG Gastrointestinal Pathogen Panel Assay for the detection of enteric pathogens in Kuwait. Med Princ Pract. 2016;25:472-476.

Sherry Dunbar, PhD, serves as Senior Director of Global Scientific Affairs for Luminex.