Fast, reliable stool analysis with NIR spectroscopy

2023. 1. 9.

문서

Despite our differences, there are some things that everyone has in common—we all consume nutrition and excrete waste (i.e., stool or feces) as a result. The phrase «you are what you eat» certainly applies when discussing the topic of stool analysis. Biomedical laboratories are equipped to test stool samples in order to diagnose a number of diseases and other issues, though conventional sample preparation and analysis procedures can be quite tedious and time-consuming. By utilizing near-infrared spectroscopy (NIRS) as an analytical technique for stool tests, laboratories can get fast, reliable results with no sample preparation.

Determination of fat, nitrogen, and dry matter content without sample preparation

The Metrohm NIRS DS2500 Solid Analyzer has been proven to be a valuable instrument for easy and reliable stool tests in biomedical laboratories. Fecal nitrogen and fat, dry matter, and many more key parameters can be quantified by NIRS in less than a minute without any sample preparation required.

Dr. Laurence Barbot-Trystram.

Dr. Laurence Barbot-Trystram from the University Hospital Pitié Salpêtrière - Charles Foix (AP-HP Paris, France) is a medical biologist and Ph.D. pharmacist specialized in biochemistry. She uses this device in her daily work and has agreed to share her experiences with the rest of the world. We asked Dr. Barbot-Trystram several questions about her work and her impressions from using the Metrohm NIRS DS2500 Solid Analyzer for stool analysis.

Click on one of the links below to jump directly to that topic.

Dr. Barbot-Trystram, could you please briefly describe your lab?
What is your role within the Functional Coprology Laboratory?
Which analyses are conducted in the Functional Coprology lab?
What convinced you to choose near-infrared spectroscopy (NIRS) for analyses in your lab?
A short introduction to NIR spectroscopy
What were the challenges you had to overcome when implementing the NIRS method?
Why did you choose Metrohm as a supplier for a NIR analyzer?
Where do you use the Metrohm NIRS DS2500 Solid Analyzer?
Sample preparation with NIR spectroscopy
What is your professional opinion about using the NIRS DS2500 Solid Analyzer for stool analysis?

1. Dr. Barbot-Trystram, could you please briefly describe your lab?

The Functional Coprology Laboratory is headed by Prof. Nathalie Kapel in the «BioGeM» department at the University Hospital Pitié Salpêtrière - Charles Foix (AP-HP Paris, France). It is recognized in France as the reference laboratory for biochemical exploration of stool and exploration of intestinal homeostasis (e.g., nutrient absorption, electrolyte secretion, fecal biomarkers, and production of bacterial metabolites).

2. What is your role within the Functional Coprology Laboratory?

As a biologist, I participate in the development and validation of new methods. Additionally, I am involved in the medical validation of results. This includes not only taking a critical analytical look at the results, but also the medical interpretation based on the confrontation between qualitative and quantitative data with those of the patient’s clinical history and symptoms.

I am also responsible for the quality assurance process and method validation according to ISO 15189 accreditation in collaboration with the other medical biologists and the technical team.

3. Which analyses are conducted in the Functional Coprology lab?

We analyze several parameters in stool samples. These include lipids, nitrogen, carbohydrates, energy, bacterial metabolites, electrolytes, calprotectin, and elastase. Such analyses help us to:

identify mechanisms behind chronic diarrhea
explore alterations of digestive functions (e.g., malabsorption)
discriminate between organic and non-organic symptoms (i.e., physically/biochemically manifested symptoms with measurable biomarkers vs. behaviorally/functionally manifested and therefore more difficult to diagnose)
explore the severity of various issues and to assess and adapt treatment management (medical and/or nutritional)

4. What convinced you to choose near-infrared spectroscopy (NIRS) for the analyses in your lab?

Reference methods for the measurement of water, lipids (fat), and nitrogen in stool are mostly manual and time-consuming. These methods require a long extraction process which leads to performing serial assays. We therefore looked for a faster analytical method that can allow the results to be rendered on an ad hoc basis. We also wanted to limit the use of solvents and to facilitate sample preparation. Near-infrared spectroscopic (NIRS) technology meets these specifications.

We chose to use NIRS for multiple reasons: the hygiene aspect, its complete automation facilitating the work for technicians, and the speed of dosages allowing a daily realization of the assay. Moreover, this analysis method provides three results at a time (i.e., lipids, nitrogen, and hydration) for the same stool sample.

Figure 1. Spectra of human feces samples resulting from the interaction of NIR light with the sample material.

5. A short introduction to NIR spectroscopy

The interaction between light and matter is a well-known process. Light used in spectroscopic methods is typically not described by the applied energy, but by the wavelength or wavenumbers.

A NIR spectrometer such as the Metrohm DS2500 Solid Analyzer measures this interaction to generate spectra as displayed in Figure 1. NIRS is especially sensitive to the presence of certain functional groups like -CH, -NH, -OH, and -SH.

6. What were the challenges you had to overcome when implementing the NIRS method?

We tested many older generation NIRS analyzers from other manufacturers but results were not satisfactory, namely for pathological samples – either watery or greasy stools. Therefore, we were quite interested in evaluating the NIRS DS2500 Analyzer from Metrohm with the new software for mathematical processing, but we had to be convinced of its performance for all kinds of fecal samples (normal as well as pathological).

7. Why did you choose Metrohm as a supplier for a NIR analyzer?

We chose Metrohm because it is both the supplier and the manufacturer. This allows us to have direct support from the company for our development and validation processes. Such a link is crucial for the implementation of newly automated processes, completely modifying our previous practices. Among all the NIRS analyzers we tried, the NIRS DS2500 Solid Analyzer is the best suited to analyze fecal samples.

Collaboration between the engineers from Metrohm and the laboratory team was essential to validate the method on pathological samples (e.g., watery, greasy, etc.).

Pre-calibrations offer a ready-to-use NIR analyzer for stool analysis right from the start:

Based on data collected from several customers using the NIRS DS2500 Solid Analyzer for stool analysis, Metrohm can offer instruments pre-calibrated for direct use.

8. Where do you use the Metrohm NIRS DS2500 Solid Analyzer?

Figure 4. The NIRS DS2500 Solid Analyzer at work in the Functional Coprology Laboratory at the University Hospital Pitié Salpêtrière - Charles Foix (Paris, France).

The fecal analyses performed on the NIRS DS2500 Solid Analyzer (lipids, nitrogen, dry weight) occur in two areas:

A routine sector that groups the main biological analyses performed for exploration of diarrhea (measurements of nutrients, electrolytes, and metabolites).
A specialized sector dedicated to nutritional assessments and the follow-up of patients who have undergone digestive surgery such as extensive intestinal resection leading to malabsorption, and wasting conditions leading to intestinal failure, bypass, or even intestinal transplantation.

9. Sample preparation with NIR spectroscopy

Figure 5. Illustration of the diffuse reflection measuring mode alongside a stool sample placed on the NIRS DS2500 Solid Analyzer.

Measurement with NIRS is straightforward. The sample is stored in an appropriate sample vessel (e.g., a petri dish) which is placed as-is on the analyzer. Stool samples are ideally measured in diffuse reflection mode. Light reflected from the sample is collected by the analyzer and used for the analysis.

Learn more about different measurement modes for all kinds of samples in our related blog post.

Benefits of NIR spectroscopy: Part 1

10. What is your professional opinion about using the NIRS DS2500 Solid Analyzer for stool analysis?

The switch from other technologies to the NIRS DS2500 Solid Analyzer was a real challenge for our team, moving from classical analytical methods to a physical technique associated with a mathematical treatment. It has resulted in interesting exchanges within the whole team, from technicians to biologists.

However, the NIRS DS2500 Solid Analyzer saves time at the technical level (e.g., preparation of samples, measurement, analyzer maintenance) allowing faster medical validation and overall a reduced turnaround time of the results to clinicians.

The software is user-friendly and sample preparation is easy to understand. We have trained several people without difficulty, including people without laboratory experience.

As the analysis is non-destructive, the sample can be recovered if necessary for other assays, which may be interesting in some cases.

The ease-of-use should not make us forget the need to look critically at the results. This spectroscopic method is not classical in biology—the interferences must first be reviewed before routine implementation is done.

Thank you, Dr. Laurence Barbot-Trystram for sharing some insights about your work. We appreciate hearing about your experiences managing the implementation of near-infrared spectroscopy into your laboratory for analysis of human fecal samples.