Reengineered credit card-sized technology improves and expands the use of stool diagnostic tests

A patient with gastrointestinal problems visits his doctor. The doctor orders a stool test that will measure fecal bile acids, compounds produced by the liver that can also be modified by the gut microbiome and are known to facilitate digestion and the absorption of lipids or fats in the small intestine.

Bile acid profiles are altered in several gastrointestinal conditions, including irritable bowel syndrome, Crohn’s disease, and several forms of diarrhea, colitis, and certain bacterial infections. The doctor hopes that the results of the examination of the stool will help identify the root cause of the patient’s condition and provide guidance on the best approach to treating the disease.

The stool sample is collected and processed, and if the collection point is different from the analytical site where the bioassay is to be performed, then the sample is stored frozen at -80°C to prevent degradation until it can be shipped. frozen on dry ice. These types of bioassays based on stool samples are usually performed using quantitative tandem mass spectrometry, the most accurate, sensitive and specific method for measuring fecal bile acids today.

The complex, multi-step process described above can be a significant barrier for remote clinical sites, for samples collected after analytical laboratory hours, or for sample collection in resource-limited settings or extreme environments.

“We wanted to generate a technology that could be used anywhere in the world and didn’t require complicated storage conditions,” said first author of a recent study, Melinda A. Engevik, PhD, assistant professor of regenerative medicine and cell biology at the University of Medicine in South Carolina.

“The solution grew naturally out of a long-term professional relationship between my laboratory, which is interested in studying metabolic products produced by microorganisms, and that of Dr. Donald Chase, chief scientist at Capitainer, who developed a mass spectrometric analysis of blood compounds that is used worldwide to screen newborns for dozens of rare genetic diseases. He has worked for more than 30 years with the dried blood spot (DBS) technology used for newborn screening,” said co-author Dr. Thomas D. Horvath, instructor of pathology and immunology at Baylor College of Medicine and Texas Children’s Hospital. .

The study was published in The American Journal of Physiology – Physiology of the Gastrointestinal Tract and Liver.

DBS technology is an efficient and practical method of collecting blood samples and transporting them in an easy and safe way to a laboratory for analysis. The blood is collected and dried on special paper on a credit card-sized pad, creating a dried blood spot. The sample is then sealed and shipped at room temperature in an envelope.

Once in the laboratory, the sample is extracted from the paper and analyzed using mass spectrometric methods. This system also avoids the biohazard precautions associated with transporting a liquid blood sample.

“It was a natural progression to explore whether DBS could be repurposed to simplify the collection, transport and analysis of other body fluids.” “In the current study, we investigated whether dried fecal spots (DFS) can be used to measure fecal bile acids,” Chase said.

Bacterial infections with C. difficile are associated with major changes in bile acid profiles, so Engevik in South Carolina collected fecal samples from individuals infected with these bacteria, as well as samples from healthy individuals and individuals with diarrhea. Engevik processed the samples, placed them in DFS paper cards and allowed them to dry. The sealed cards were shipped at room temperature to Horvath’s lab in Houston.

“We didn’t use dry ice and bulky containers for storage and transport,” Engevik said.

The researchers kept the samples at room temperature in Horvath’s lab for four months. They then analyzed the bile acid content of the DFS samples and compared the results to reference extracts from “liquid state” samples that had been stored at -80°C for the same four-month time period.

“We were very excited when the results showed no significant differences in the amount of bile acids in both DFS and frozen fecal samples,” said Horvath.

“These findings prove the concept that DFS provides reliable results for the bile acid content of fecal samples that are comparable to those obtained by the traditional method, but offer the advantages of easier storage and transportation, reduced costs, and improved safety.”

“I think this work has the potential to change the way samples are processed in remote settings, and that has huge global implications,” Engevik said.

“For example, scientists doing research work in the field or doctors serving patients in remote areas can collect faecal samples using the DFS cards, store them in an envelope and carry the samples without having to freeze them until they arrive in their laboratory for analysis, even months later.”

“We also envision DFS as a system that allows people to collect fecal samples from their own home and then send the card to the analytical lab, saving them a trip to the doctor’s office,” Horvath said.

“Now that we know our system can accurately measure bile acids, we’re excited about measuring other fecal compounds as well as those produced by microorganisms,” Chase said.