Lung Ultrasound May Help Diagnose Acute Chest Syndrome in SCD
Analysis finds ultrasound may be better than chest X-rays for diagnosis
A lung ultrasound may help in diagnosing acute chest syndrome (ACS), a serious lung complication in sickle cell disease (SCD), a pooled analysis of studies suggests.
In fact, according to researchers, a lung ultrasound may be a better option than repeated chest X-rays to support an ACS diagnosis. An ultrasound offers lower costs, ease of use — particularly among children — and a lack of exposure to radiation.
“Lung ultrasound … is emerging as a point-of-care method to diagnose ACS, allowing for more rapid diagnosis in the emergency room setting and sparing patients from ionizing radiation exposure,” the investigators wrote.
Further research is needed, however, to “determine the utility of lung ultrasound as a potential diagnostic, monitoring, and predictive tool in the management of ACS in SCD,” the team noted.
Findings from the pooled analysis were detailed in a study, “Diagnostic Test Accuracy of Lung Ultrasound for Acute Chest Syndrome in Sickle Cell Disease: A Systematic Review and Meta-analysis,” published in the journal CHEST.
Potentially a better diagnostic tool than X-rays
Acute chest syndrome, known as ACS, is marked by fever, chest pain, and difficulty breathing, and is a main cause of hospitalization and death in SCD patients.
The condition is diagnosed based on the presence of lung symptoms and/or fever, as well as lung infiltrates on chest X-rays. Such infiltrates are a sign of fluid, pus, or blood buildup in the lungs.
Although its criteria are well-defined, diagnosing ACS in a real-world setting can be challenging because the clinical presentation can vary widely between patients, especially without imaging data. Also of note, repeated exposure to X-ray or CT scan radiation can be harmful in the long term.
Lung ultrasound is a safe, portable, and convenient method that uses sound waves to visualize the inside of the lungs and is widely used to diagnose lung conditions like pneumonia. A recent study conducted in Brazil and Canada suggested that lung ultrasound was more reliable than chest X-rays for ruling out ACS in children with SCD.
Now, a team led by researchers at the University of Pittsburgh School of Medicine, in Pennsylvania, conducted a pooled analysis of several studies that investigated the accuracy of ACS diagnosis by lung ultrasound. Such pooled analyses are known as a meta-analysis.
Researchers selected six eligible studies with data that compared lung ultrasound with standard chest X-ray and provided the number of SCD patients who were accurately identified as having or not having ACS.
Among the studies, participants ranged in age from 5 to 41, and 41% were female. Of 625 suspected ACS cases, 95 (15.2%) were confirmed to be acute chest syndrome. Notably, 97% of these patients were age 21 or younger.
The most commonly reported symptoms included coughing and chest pain, followed by non-chest pain, fever, vomiting, and other lung symptoms.
While the criteria for ACS diagnosis using X-rays was consistent across studies, the standard diagnostic criteria for the condition using ultrasound “was not clearly established,” the team noted.
Compared with the reference standard of chest X-ray, lung ultrasound’s sensitivity (true-positive rate) to detect ACS was 92%, while its specificity (true-negative rate) was 89%.
The proportion of SCD patients who tested positive and were eventually diagnosed with ACS, or the positive predictive value, was 88%. In comparison, the negative predictive value for lung ultrasound was 90%, reflecting the proportion of those without signs of ACS via lung ultrasound who did not have the condition.
Results were similar in a sensitivity analysis, in which abstract-only studies reporting summarized data were excluded from the analysis.
[Lung ultrasound] may be a valuable tool in the evaluation of ACS in patients with SCD due to the lack of radiation exposure, low cost, and ease of use
Further statistical calculations found the probability of finding ACS before a test was 15.2%. This probability rose to 60% with a positive lung ultrasound test and fell to 2% with a negative result.
Although this pooled analysis included only six studies, researchers noted there was a low risk of publication bias — in which the outcome of the studies influenced (biased) the decision to publish.
“The results of our meta-analysis demonstrate that [lung ultrasound] may be a valuable tool in the evaluation of ACS in patients with SCD due to the lack of radiation exposure, low cost, and ease of use, especially in pediatric populations,” the researchers concluded.