investigations

Last reviewed 01/2021

The investigation of a pleural effusion in primary care should include the following:

  • 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 (2)
    • 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 (2)
  • 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
  • transthoracic echocardiography
  • 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

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