The neutrophil to lymphocyte ratio (NLR) — a measure of inflammation calculated by dividing the number of different immune cells — can be used as a biomarker of exacerbations induced by bacterial infections in patients with bronchiectasis, a study suggests.
The study, “Neutrophils to Lymphocyte Ratio as a Biomarker in Bronchiectasis Exacerbation: A Retrospective Study,” was published in the journal Cureus.
Bronchiectasis is a lung disease in which the bronchi, or small lung airways, become inflamed due to recurrent or chronic infections. Over time, these small airways become irreversibly thicker and larger. People with bronchiectasis also tend to produce large amounts of mucus that can trap harmful bacteria, which in turn causes lung infections.
Exacerbations or flare-ups in bronchiectasis — that is, periods of time in which symptoms worsen — are normally caused by bacterial infections that lead to the recruitment of immune cells called neutrophils to the lungs.
Once inside the lungs, the neutrophils start releasing a series of enzymes that end up destroying the extracellular matrix (ECM), which is the network of proteins and other substances that surrounds and supports cells as a type of structural scaffold. Such damage leads to reduced mucus clearance and to continued inflammation in the airways.
Here, researchers in Greece reported a study that sought to determine if NLR, a marker of inflammation calculated by dividing the number of neutrophils by the total number of white blood cells, could be a useful biomarker of exacerbations in people with bronchiectasis.
To that end, the investigators analyzed data from 80 patients (54 men and 26 women, with a mean age of 77.3 years) with a diagnosis of bronchiectasis. Participants had already experienced exacerbations and had been hospitalized between January 2016 and January 2019 at one of two hospitals in Athens.
Collected data included several blood-cell counts, which were used to calculate the NLR, as well as the levels of C-reactive protein (CRP), another marker of inflammation that was compared to the NLR.
In addition, the team analyzed data from sputum cultures, which had been performed in all patients. The purpose of these cultures is to detect the presence of bacteria or fungi causing lung infections.
A total of 64 healthy individuals (36 men and 28 women, with a mean age of 62.9 years) were also included in the analyses as controls.
Results showed that, compared with the healthy controls, patients with bronchiectasis had higher mean NLR values (9.2 vs. 3.1). However, no significant association was found between NLR values and CRP levels in these participants.
From the 80 patients included in the analyses, 52 had bacteria or other type of microbes in their sputum cultures, thereby being positive cultures. The bacteria Pseudomonas aeruginosa, which frequently cause lung infections, were identified in 24 patients.
The researchers also discovered that NLR values tended to be higher in patients with positive sputum cultures, compared with those with negative cultures (10.5 vs. 6.7). However, no significant differences were found comparing those whose cultures contained P. aeruginosa and patients whose infections were caused by other microbes (10.1 vs. 10.8).
“NLR can be used for predicting positive cultures in patients with bronchiectasis exacerbation,” the scientists concluded. “Further investigation is needed to establish the diagnostic significance of this marker in patients with bronchiectasis exacerbation – maybe a study comparing NLR values between patients with stable bronchiectasis and patients with exacerbation.”
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