The prevalence of lung surface abnormalities in a healthy population as detected by a screening lung ultrasound protocol: Comparison between young and older volunteers

Outline: Lung ultrasound can detect B-lines in both disease states and normal patients. B-lines are sensitive indicators for interstitial oedema, but research is limited in terms of what is a 'normal' amount in healthy adults. Current belief is that 3 B-lines in laterobasal areas can be normal. We aimed to determine what is normal in healthy patients of different ages. We hypothesised that older patients and patients with the previous history of lung disease or smoking would have more B-lines.

Methods: We performed a cross-sectional study on a convenience sample of 200 volunteers: 100 aged 18-49 (median age 33.5) and 100 aged 50-91 (median age 70.5). Volunteers were recruited in 2017 from two participating sites. All participants were scanned by a single researcher using a standardised lung protocol. Multivariate regression was conducted to determine independent predictors of B-line presence.

Results: B-lines were found in 12.5% (95%CI: 8.4-17.6) of all volunteers (n = 25/200), with 20% (95%CI: 13.3-28.9) prevalence in the younger group and 5% (95%CI: 1.9-10.7) in the older group (P < 0.0001). A total of 84% (95%CI: 65.3-93.6) had only 1 B-line (n = 21/25). 31.3% (95%CI: 20.0-45.6) of young females had B-lines. Only one volunteer had ≥3 B-lines in one scanned area. Participants with chronic lung disease had more B-lines (P = 0.03). Smokers (n = 13) also had more B-lines (31% vs. 11% of non-smokers). Smoking and younger age were independent predictors of B-line presence multivariate logistic regression models, but only for females.

Conclusion: ≥2 B-lines are uncommon in healthy, ambulatory adults. Further research is needed to investigate the higher prevalence found in young females.