When sampling techniques matters

Induced and spontaneous sputum sampling are techniques used to study lung inflammation and microbes and are less invasive alternatives to a bronchoscopy. But can choice between these two sampling techniques impact researchers’ conclusions when examining a patient’s lungs? Solveig Tangedal, lead author of new research published in Respiratory Research exploring this issue, tells us more.

Patients suffering from different lung diseases can experience intermittent deterioration of their health – exacerbations. In chronic obstructive lung disease (COPD) these episodes often lead to reduced quality of life, lung function and life expectancy. Researchers are working to unravel the mechanisms behind COPD exacerbations and to find ways to reduce their frequency and negative impact on patients.

Studying the lungs with regards to both inflammation and microbes is important when pursuing knowledge on processes in the lungs and trying to identify targets for treatment. In specialized health care departments sampling of the lungs can be done directly through insertion of a bronchoscope into the lower airways if the patients are fit to undergo such a procedure. In some cases this is not possible, and an alternative sampling technique is called for. Sputum is as a result frequently used in lung research.

We realized that we had many induced and many spontaneous sputum samples, but did not know whether it would be good practice to use both types in one study

Sputum sampling is less invasive and associated with fewer complications for the patients than bronchoscopy, and also demands fewer resources. Some patients have a rich sputum production allowing for spontaneous sampling, others must inhale saline solutions that will lead to an increased production of sputum in the airways before they can cough up a sample for analyses (induced sampling).

But can choice of sputum sampling techniques affect researchers’ conclusions on inflammatory processes and bacterial composition? In Bergen, Norway, two large COPD studies The Bergen COPD Cohort Study (BCCS) and Bergen COPD Exacerbation Study (BCES), included multiple sputum samplings during the years of 2006 – 2010.

Joining the project in 2013 I wanted to use sputum samples to evaluate both inflammatory markers and the microbiota in COPD. We realized that we had many induced and many spontaneous sputum samples, but did not know whether it would be good practice to use both types in one study.

Meanwhile some patients had delivered paired sputum samples – both a spontaneous and an induced sample taken sequentially on the same visits at the hospital. We therefore decided to analyze these paired samples and run comparisons between them to evaluate similarities and differences before allowing ourselves to use sputum without regards to sampling techniques.

The first study compared inflammatory markers in pairs of sputum and we concluded that when studying inflammation it would be advisable to use either induced samples or spontaneous samples, but not both.

Standardization of methodology in research is important to allow researchers to compare results from different studies

In our current study the evaluation of induced and spontaneous sputum was focused on the bacterial composition and diversity. We found frequent dissimilarities within paired sputum. This is indicative of studying microbiota in sputum researchers should strive to sample patients using the same technique even when the material studied is similar.

Standardization of methodology in research is important to allow researchers to compare results from different studies. In the field of human microbiota – the study of the vast bacterial community inhabiting our bodies – the technical development is rapid and the need for guidelines with regards to sampling and analyses great.

With our comparisons of paired sputum samples we cast light on the importance of concise and standardized operational procedures. Whether one sputum type is to be preferred over the other is not yet addressed and will demand a larger number of sputum pairs to be analyzed.

We hope that ongoing studies on patients suffering from COPD will bring us closer to an understanding of the processes leading to their health challenges, and to targeted treatments improving quality of life and life expectancy. Still the most important message remains: Avoid smoking and get your daily exercise!

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