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Ultrasound scans of the lungs can be more accurate than chest X-rays for diagnosing pneumonia in children in some circumstances.

A review of the published evidence found that lung ultrasound was more sensitive (missed fewer cases) and about as specific (gave about the same number of false alarms) as chest X-ray, when used to confirm suspected community-acquired pneumonia in children. While pneumonia is a clinical diagnosis, X-ray is often used for confirmation.

Ultrasound also spares the child from the radiation associated with X-ray imaging.

Many emergency departments already use ultrasound, so it might be practical to train paediatric staff to use it as a first-line test. However, the study found variation in the specific ultrasound findings that teams used to diagnose pneumonia, suggesting more work needs to be done to clarify diagnostic criteria.

Why was this study needed?

Community-acquired pneumonia is a major cause of childhood mortality worldwide, although rates of infection in developed countries are relatively low, at 34 to 40 cases per 1,000 children under five years old per year.

Pneumonia is primarily a clinical diagnosis and, in the UK, national targets exist to reduce the proportion of children given X-ray where there is no clinical evidence of severe or complicated pneumonia. However, around 73% of children in the UK with suspected community-acquired pneumonia were given a chest X-ray in 2016-17. This suggests that radiological confirmation of the diagnosis is routine in many hospitals.

While the radiologic gold standard for diagnosis is computed tomography, this is expensive and exposes the child to more radiation. This research aimed to test if ultrasound might be a reliable low-risk alternative to chest X-ray and if staff can be trained in its use for diagnosing pneumonia.

What did this study do?

This systematic review and meta-analysis pooled 12 studies of 1,510 children that compared chest X-ray with lung ultrasound to diagnose community-acquired pneumonia in children.

The children’s ages ranged from 1 month to 21 years with an average of four years. All the studies compared the diagnostic accuracy of lung ultrasound with chest X-ray, using either expert paediatrician clinical diagnosis or expert diagnosis plus chest X-ray as the reference standard.

The researchers looked separately at two studies where less experienced sonographers were trained to make the diagnosis.

There was variability between the studies regarding ultrasound diagnostic criteria which may have affected the comparability of results. In those studies where X-ray was also used in the clinical reference standard, the specificity of chest X-ray might have been overstated.

What did it find?

  • Lung ultrasound was more sensitive than chest X-ray. Lung ultrasound picked up 95.5% of children later confirmed clinically as having pneumonia (95% confidence interval [CI] 93.6 to 97.1) and chest X-ray picked up 86.8% of cases (95% CI 83.3 to 90.0).
  • Lung ultrasound and chest X-ray had similar levels of specificity. Lung ultrasound correctly identified 95.3% of children who did not have pneumonia (95% CI 91.1 to 98.3) and chest X-ray correctly identified 98.2% of them as clear of infection when they did not have pneumonia (95% CI 95.7 to 99.6).
  • Eleven of the 12 studies found discrepancies between the lung ultrasound and chest X-ray results. In total, 112 cases of pneumonia were found on lung ultrasound but not on X-ray, while 35 cases of pneumonia were found on X-ray but not lung ultrasound.
  • Positive predictive values (PPV) and negative predictive values (NPV) were similar. Lung ultrasound had a PPV of 99.0% (95% CI 97.9 to 99.8) and of 63.1% (95% CI 40.8 to 82.8). Chest X-ray had a PPV of 99.6% (95% CI 99.2 to 99.9) and a NPV of 43.6% (95% CI 20.6 to 68.2).

What does current guidance say on this issue?

British Thoracic Society guidelines on paediatric community-acquired pneumonia were archived in 2017, as they were more than five years old. They stated, “Bacterial pneumonia should be considered in children when there is persistent or repetitive fever > 38.5°C together with chest recession and a raised respiratory rate.”

They added: “Chest radiography should not be considered a routine investigation in children thought to have community-acquired pneumonia”.

Where history and clinical signs strongly suggest pneumonia, then treatment should be started. The benefit of additional tests is not clear

What are the implications?

The study shows that lung ultrasound may be a viable and accurate alternative to chest X-ray for confirming a clinical diagnosis of community-acquired pneumonia in children. If ultrasound could replace at least some of the X-ray investigations in emergency departments, it would spare children a dose of radiation.

The introduction of lung ultrasound as a routine test for paediatric community-acquired pneumonia would require clearer criteria for the ultrasound findings considered diagnostic. It would also involve training staff to make the diagnosis using ultrasound, but this cost might be offset by a reduction in the need for X-ray.

Citation and Funding

Balk DS, Lee C, Schafer J, et al. Lung ultrasound compared to chest X-ray for diagnosis of pediatric pneumonia: A meta-analysis. Pediatr Pulmonol. 2018; Apr 26. doi: 10.1002/ppul.24020.

No funding information was provided for this study.



Harris M, Clark J, Coote N, Fletcher P, et al; British Thoracic Society Standards of Care Committee. British Thoracic Society guidelines for the management of community acquired pneumonia in children: update 2011. Thorax. 2011;66 Suppl 2:ii1-23.

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Sensitivity is the ability of the test to correctly identify those with a disease. Specificity is the ability of the test to correctly identify those without the disease. Positive predictive value is the likelihood of a positive test predicting the correct outcome. Negative predictive value is the likelihood of a negative test predicting the correct outcome.  
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