Pleural effusion

As a foundation doctor, shortness of breath is one of the commonest symptoms you can encounter on the acute take. Causes of shortness of breath are very broad but in this session, we will discuss pleural effusion. The management will vary depending on the causes of pleural effusion, therefore the diagnostic approach is important.

The first step is confirmation of pleural effusion clinically or radiologically (chest x-ray or ultrasound).

History and examination

Symptoms: dyspnoea, cough, and pleuritic chest pain

Associated symptoms: any fever in case of empyema, unintentional significant weight loss and anorexia in cases of malignancy.

Onset: If the patient presents with gradual onset breathlessness, we can think of causes like congestive heart failure. A pleural effusion that develops subsequent to pneumonia could lead us to suspect a parapneumonic effusion. If the onset is acute and occurs following trauma, we should suspect haemothorax and urgent management would be needed. 

Past medical history: congestive heart failure (CHF), renal failure, cirrhosis, lupus pleuritis, or rheumatoid arthritis, previous malignancy (relapse could lead to pleural effusions eg. breast cancer with lung metastases), previous TB or contact with TB patients

Full occupational history: Asbestos exposure

Full medication history: nitrofurantoin, dantrolene, sodium valproate, propylthiouracil, isotretinoin, and tyrosine kinase inhibitors

Examination: absent breath sounds, dullness to percussion, decreased or absent tactile fremitus, and decreased vocal transmission over the base of the lung strongly suggest a fluid collection.


  • atelectasis/lobar collapse
  • pneumothorax following thoracocentesis
  • re-expansion pulmonary oedema
  • pleural fibrosis
  • trapped lung
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Chest X-Ray (PA view)
  • Meniscus sign: fluid will surround the lung base forming a meniscus (a concave line obscuring the costophrenic angle and part or all of the hemidiaphragm), there may be a contralateral mediastinal shift
  • Air-fluid levels indicate a hydropneumothorax; air and liquid in the pleural space 
  • A subpulmonary effusion localized below the lower lobes can give the appearance of an elevated diaphragm
Images taken from and
Image taken from
Pleural Ultrasound
  • Useful in locating an area of fluid collection for thoracentesis, especially if the effusion is loculated or small. 
  • More sensitive and specific than chest X-ray for pleural effusion detection, can detect septations within a pleural collection.
  • Can identify 5 to 10 mL of fluid
Image taken from
Pleural fluid analysis :
  • LDH and protein in pleural fluid and serum indicate an exudate if the ratio of pleural fluid protein to serum protein is >0.5, if the ratio of pleural fluid LDH to serum LDH is >0.6, or if the pleural fluid LDH is greater than two-thirds of the normal upper limit of serum LDH. This is also called Light’s criteria
  • Protein gradient: A protein gradient between serum and pleural fluid of ≥31 g/L (3.1 g/dL) indicates a transudate
  • WBC count and differential of pleural fluid : >50% lymphocytes may suggest malignancy or TB. If lymphocytes is >90% lymphocytes, lymphoma and TB are the most likely diagnoses.
  • Cytology: positive in >60% of malignant pleural effusions
  • Culture and sensitivity: positive microbial growth in parapneumonic effusion or empyema
  • pH of pleural fluid: <7.20 in empyema, parapneumonic effusion, rheumatoid arthritis or advanced malignancy
  • Red blood cell count in pleural fluid: >100,000 RBC/mm³ in malignancy, trauma, parapneumonic effusions, and pulmonary embolism
  • Glucose in pleural fluid: <3.3 mmol/L (60mg/dL) in empyema, rheumatoid arthritis, TB and malignancy
  • ADA: elevated (>40 U/L) in TB
  • Lipid analysis of pleural fluid: The presence of chylomicrons on microscopy confirms a chylothorax, and a high triglyceride level, usually >1.24 mmol/L (110 mg/dL), is diagnostic.


Blood tests: FBC, CRP, Blood cultures

Radiology: CT thorax, MRI thorax

Thoracoscopy: It should be considered if the patient is not improving, the cause of the effusion is unknown, or cytology is negative when pleural malignancy is suspected


The treatment of a pleural effusion is dictated by the underlying cause. Symptomatic patients with large effusions may be treated by therapeutic aspiration (thoracocentesis).

  • Infective: Gram-positive bacteria are the most common pathogens in community-acquired parapneumonic effusions. Empirical intravenous antibiotics can be given based on local microbiology guidelines to cover the likely causative organisms, both aerobic and anaerobic.
  • Malignancy: if the patient has good performance status – pleurodesis or pleural catheter drainage + physiotherapy + oxygen. If the patient has poor performance status – therapeutic thoracentesis + physiotherapy + oxygen. Talc, bleomycin, and tetracycline are commonly used agents.
  • Persistent empyema despite chest drain: direct visualisation (thoracoscopy or VATS) and lysis of adhesions
  • Recurrent benign effusion: may occur in various conditions such as inflammatory, infectious, or other systemic diseases (e.g., congestive heart failure, post-lung transplantation and chronic exudative pleurisy etc). Medical or surgical thoracoscopy could be considered for diagnostic purposes.
  • Physiotherapy and Oxygen therapy can be given as adjunctive therapy to all patients with pleural effusion 


Written by Dr YiYi Aung (JSD)

Reviewed by Dr Geraldine Quintero-Platt (Consultant)

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