Investigations

The investigation of a pleural effusion in primary care should include the following: (1,2)

• AP chest radiograph:
  • posteroanterior (PA) chest x-rays should be performed in the assessment of suspected cases
  • an abnormal PA chest x-ray is seen with the presence of about 200 ml of pleural fluid while 50ml will produce detectable posterior costophrenic angle blunting on a lateral chest x-ray
  • water-dense shadow with a concave-upwards upper border
  • classic “white-out” of the affected hemithorax may be seen in large effusions
  • a collection of fluid in the pleural space beneath the inferior surface of the lung (subpulmonic effusion) may mimic an elevated hemidiaphragm - in this case a lateral decubitus X-ray or ultrasound examination is discriminatory
  • radiography may provide aetiological information:
    • cardiomegaly is suggestive of congestive cardiac failure
    • a bronchial neoplasm or other malignancy may be seen
    • cavitating consolidation suggests tuberculosis
  • the volume of pleural fluid is commonly underestimated on a supine chest x-ray and ‘normal’ appearances do not exclude the presence of an effusion
• ultrasonography
  • US is more sensitive than x-ray in identifying effusions.
• blood tests- for evidence of infection, blood loss, or platelet abnormality
• liver and renal function
• serum NT-pro brain natriuretic peptide

Following investigations are usually carried out in secondary care

• diagnostic pleural aspiration:
  • a green needle (21G) and 50 ml syringe are used
  • bedside ultrasound guidance improves the success rate and reduce complications
  • is the first routine invasive step in the investigation of a pleural effusion
  • before the procedure obtain consent from patients for the possibility of pneumothorax, pain, haemorrhage, and underlying visceral damage
• contrast enhanced computed tomography
  • usually carried out after confirming collection of fluid on chest radiography or ultrasonography and after initial sampling
• pleural biopsy
• transthoracic echocardiography

References

1. Expert Panel on Thoracic Imaging, Morris MF, Henry TS, et al. ACR Appropriateness Criteria® Workup of pleural effusion or pleural disease. J Am Coll Radiol. 2024 Jun;21(6):S343-52.
2. Roberts ME, Rahman NM, Maskell NA, et al. British Thoracic Society guideline for pleural disease. Thorax. 2023 Jul;78(suppl 3):s1-42.