The Role of Breath Analysis in Diagnosing Disease

Key breath metabolites
Common techniques associated with breath analysis
Collection and analysis of stored breath samples
Diagnosis of disease using volatile biomarkers
Commercial production of breath analyzers for disease detection
References 
Further reading

Breath is an important matrix for analyzing volatile organic compounds (VOCs) that are generated within the body. These compounds travel through the blood in the body, reach the alveolar interface, and are ultimately exhaled. The analysis of exhaled breath to detect VOCs could indicate the diseased or healthy state of an individual.

Researchers have documented the evidence of the presence of detectable VOCs in the breath related to breast and lung cancer. The scientific community has been extremely interested in identifying all parameters influencing the presence of VOCs in exhaled air. In this context, it has focused on standardizing the methodology for breath sampling and analysis. Breath analysis may lead to rapid and non-invasive detection of various diseases, such as diabetes and cancer.

Key breath metabolites 

Typically, exhaled breath consists of unmodified nitrogen (~ 74%), argon (~1%), oxygen (~15%), carbon dioxide (~ 5%), and water vapour (~6%). In addition, several endogenously formed gaseous volatile metabolites are present in the exhaled breath at trace levels, which are measured in parts per million volume (ppmv), parts per trillion volume (pptv), or parts per billion volume (ppbv).

Researchers have detected common breath metabolites in several healthy individuals for thirty days, such as acetone, methanol, ammonia, acetaldehyde, propanol, isoprene, and ethanol. These metabolites were detected via the Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) method. Variability in concentrations of these metabolites was assessed, and the log-normal distribution for these metabolites was studied. 

Ammonia is present in the body as a breakdown product of proteins via bacterial degradation in the intestine. Although a large part of ammonia is converted into urea and is eliminated through urine, a small part is expelled from breath. The concentration of ethanol and methanol may increase due to anaerobic fermentation by gut bacteria. The presence of isoprene in human breath has been considered a marker of cholesterol synthesis. Additionally, scientists revealed that an abnormal level of isoprene in human breath indicates end-stage renal failure and oxidative stress.

Common techniques associated with breath analysis

Two of the analytical tools used to analyze breath for detecting and quantifying trace gases in real-time with high sensitivity are Proton Transfer Reaction Mass Spectrometry (PTR-MS) and SIFT-MS. Both PTR-MS and SIFT-MS are known as soft ionization techniques that can detect biomarkers present in the breath samples, ranging from ppbv to pptv. Although SIFT-MS is less sensitive than PTR-MS, it is advantageous because it does not employ an electric field and reactions occur under thermal conditions.

Researchers have also used ion mobility spectrometry (IMS) and laser absorption spectroscopy (LAS) in breath analysis. Cavity ringdown spectroscopy (CRDS), based on LAS has been used to measure nitrous oxide (NO) in exhaled breath. This technique can quantify VOCs in breath below parts-per-billion by volume levels. 

Electron Noses (e-Noses) is an electronic sensing device that contains an array of gas and semiconductor-based sensors. Two mass-sensitive sensors-based devices, namely, quartz crystal microbalance (QCM) and the surface acoustic wave (SAW), are used in breath analysis.

Collection and analysis of stored breath samples

Direct sampling is preferable for the analysis of breath because it limits the possibility of a loss of compounds by diffusion or sample degradation. However, in the scenario where direct sampling is not possible, a suitable storage system of exhaled breath is an important aspect. Scientists indicated the risk of contamination of the breath samples with background emission of pollutants, which might alter the chemistry of the stored samples.

At present, inert Tedlar bags with many advancements are manufactured by many companies, such as Dupont and SKC Ltd. These bags are transparent or black and are based on various components, such as Nalophan, Flexfoil, and Teflon. Previous studies have indicated that Nalophan bags are low-cost and most popular for collecting breath samples. The stability of the breath components in Tedlar bags has been determined by gas chromatography-MS (GC-MS) and PTR-MS.

The stored breath has been analyzed for the presence of VOCs via various methods like the needle trap micro-extraction (NTME) combined with GC and Solid phase microextraction (SPME). 

Diagnosis of disease using volatile biomarkers

Scientists assessed SIFT-MS and PTR-MS technologies to determine if they can detect liver disease and monitor diabetes. In addition, these techniques were also assessed for the diagnosis of various types of cancers such as lung, colorectal, bladder, and prostate.

In the context of early detection of lung and breast cancers, methylated hydrocarbons were proposed as biomarkers. Scientists stated that the presence of acetaldehyde in the exhaled breath above 22 ppb could have major clinical importance. Although acetaldehyde is an intermediate product in the metabolism of ethanol in the liver, intake of alcohol significantly elevates its levels in the breath. Scientists determined the molecular emission from cancer cell lines CALU-1 and SK-MES and found its presence higher than physiological levels.

VOCs produced by gut bacteria are transported to and excreted by the lungs. For instance, VOCs released by Helicobacter pylori in the human stomach can be detected in the mouth-exhaled air. Helicobacter pylori infect the stomach and gut, damages the tissues of the stomach lining, and causes inflammation. This pathogen causes peptic ulcers in humans.

Scientists have designed a breath analyzer for the detection of pulmonary tuberculosis. In this case, the biomarker compounds detected are methyl p-anisate, methyl phenylacetate, o-phenylanisole, and methyl nicotinate.

Commercial production of breath analyzers for disease detection

Owlstone was formed by a group of scientists from the University of Cambridge, which manufactured and sold "Field Asymmetric Ion Mobility Spectrometry (FAIMS)." Their "Breath Biopsy" technology can accurately profile VOCs present in breath samples.

Breath Diagnostics, a Kentucky-based start-up company, developed a breath diagnostic device for lung cancer. It stated that their device could distinguish benign tumors from malignant tumors 77% of the time. 

New England Breath Technologies is a Massachusetts-based start-up company, which was founded in 2015. This company developed a breath analyzer for the detection of blood sugar levels. Their product is called Glucair, which detects the concentration of acetone in an individual's breath

References

• Lourenço, C. and Turner, C. (2014) "Breath Analysis in Disease Diagnosis: Methodological Considerations and Applications", Metabolites, 4(2), pp. 465-498. doi: 10.3390/metabo4020465.
• Kaloumenou, M. et al. (2022) "Breath Analysis: A Promising Tool for Disease Diagnosis—The Role of Sensors", Sensors, 22(3), p. 1238. doi: 10.3390/s22031238.
• (2022) Cen.acs.org. Available at: https://cen.acs.org/articles/82/i13/BREATH-ANALYSIS-MEDICAL-DIAGNOSIS.html (Accessed: 23 June 2022).
• Transforming disease detection: The power of breath analysis (2021). Available at: https://www.medicaldevice-network.com/sponsored/transforming-disease-detection-breath-analysis/ (Accessed: 23 June 2022).
• Mule, N., Patil, D. and Kaur, M. (2021) "A comprehensive survey on investigation techniques of exhaled breath (EB) for diagnosis of diseases in human body", Informatics in Medicine Unlocked, 26, p. 100715. doi: 10.1016/j.imu.2021.100715.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.