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
- 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
References:
- 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.
- Roberts ME, Rahman NM, Maskell NA, et al. British Thoracic Society guideline for pleural disease. Thorax. 2023 Jul;78(suppl 3):s1-42.