What are the most common causes of a pleural effusion in Australia?

Heart failure is the single most common cause, accounting for around half of all effusions — usually presenting as a bilateral transudate with other signs of fluid overload. Parapneumonic effusion from community-acquired pneumonia is the second most common, presenting as a unilateral exudate with fever and productive cough. Malignancy — most often lung cancer, breast metastases, lymphoma, or mesothelioma — accounts for around 15% of effusions. Mesothelioma is a particular Australian concern given high historical rates of occupational asbestos exposure in mining, construction, and shipbuilding industries.

What is Light's criteria and why does it matter?

Light's criteria, established in 1972 and still the international standard, classify pleural fluid as an exudate if any one of three conditions is met: pleural protein divided by serum protein is greater than 0.5; pleural LDH divided by serum LDH is greater than 0.6; or pleural LDH is above two-thirds the upper limit of normal serum LDH. Exudate means there is an inflammatory, neoplastic, or lymphatic process driving fluid accumulation — requiring specific investigation. Transudate means a pressure or oncotic cause — often manageable without diagnostic tapping if the clinical cause is clear.

When does a pleural effusion need draining?

A therapeutic drain is indicated when a large effusion causes significant breathlessness that is not responding to treating the underlying cause. Drainage is also required for empyema — infected pleural fluid with pH below 7.2, glucose below 2.2 mmol/L, or positive Gram stain — which needs a chest drain as soon as it is confirmed. Recurrent malignant effusions that keep coming back are managed with an indwelling pleural catheter (a soft tube allowing home drainage two to three times weekly) or chemical pleurodesis. A single therapeutic tap is limited to 1,500 mL to avoid re-expansion pulmonary oedema.

What should I do if I find an effusion in a patient with asbestos exposure history?

Treat it as potentially mesothelioma until proven otherwise, regardless of how long ago the exposure was — mesothelioma has a latency of 20–50 years from asbestos exposure. Order urgent CT chest with contrast and refer to a respiratory physician or mesothelioma multidisciplinary team. Tissue biopsy (CT-guided pleural biopsy or thoracoscopy) confirms the diagnosis. Simultaneously, document the occupational history carefully and make a warm referral to the state asbestos disease compensation scheme — NSW Dust Diseases Tribunal, WorkSafe VIC, WorkCover Queensland, or equivalent — because compensation claims require early documentation.

Can tuberculosis cause a pleural effusion and how is it diagnosed?

Yes. Tuberculous pleuritis is an important cause of unilateral lymphocyte-predominant exudative effusion, particularly in patients from TB-endemic countries — a common presentation in Australian general practice given our migrant population from South-East Asia, Sub-Saharan Africa, South Asia, and Pacific Island nations. Standard AFB smear has low sensitivity in pleural fluid. The adenosine deaminase (ADA) level elevated above 40 U/L in a lymphocyte-predominant exudate is 90% sensitive and specific for TB pleuritis. Mycobacterial culture takes 6–8 weeks; pleural biopsy provides the highest diagnostic yield. Notification to the state TB program is mandatory on diagnosis.

Pleural effusion

Pleural effusion: Light's criteria, diagnosis, and management

By Dr HB Lo, FACRRM Reviewed 13 August 2026 11 min read

A pleural effusion is abnormal fluid in the pleural space between lung and chest wall. The diagnostic priority is categorising it as transudate (heart failure, cirrhosis, nephrotic syndrome) or exudate (pneumonia, malignancy, tuberculosis, mesothelioma), using Light's criteria applied to pleural fluid biochemistry.

Treatment targets the underlying cause: diuresis for cardiac transudates; antibiotics and chest drain for empyema; systemic therapy and indwelling pleural catheter for recurrent malignant effusions. In Australia, any unilateral effusion with asbestos exposure history requires expedited specialist referral alongside the state workers' compensation pathway.

A pleural effusion is abnormal accumulation of fluid in the pleural space — the normally near-empty cavity between the visceral pleura covering the lung and the parietal pleura lining the chest wall. At baseline, fewer than 10 mL of lubricating fluid is present. Even 200 mL may not be visible on a posteroanterior chest X-ray; 500 mL produces a clear fluid level at the lung base.

The central diagnostic task is categorising fluid as transudate — arising from pressure or oncotic imbalance — or exudate — arising from an inflammatory, neoplastic, or lymphatic process. This distinction, formalised in Light’s criteria, directs the investigation efficiently and determines urgency. A bilateral transudate in decompensated heart failure needs diuretics, not a pleural tap; a unilateral exudate in a patient with weight loss and haemoptysis needs CT and urgent referral.

General practice contributes three things: recognising the clinical presentation, initiating the investigation pathway, and coordinating specialist follow-up — including, in the case of mesothelioma, the compensation and medico-legal pathway that is as important as the treatment pathway.

A. Core clinical — the AU general-practice framework

Recognising the presentation

Symptoms vary with effusion size and the rate of accumulation:

Dyspnoea — the cardinal symptom; exertional at first, progressing to rest dyspnoea with large effusions
Pleuritic chest pain — sharp, worse on inspiration; implies parietal pleural inflammation (pneumonia, pulmonary embolism, pleuritis)
Dry cough — from lung compression
Systemic symptoms that point to underlying cause: fever and productive cough (pneumonia, empyema), weight loss and night sweats (malignancy, tuberculosis), orthopnoea and ankle swelling (heart failure), jaundice and ascites (cirrhosis)

Examination at the lung base on the affected side:

Stony dull percussion — the hallmark; the quality of dullness distinguishes effusion from consolidation (which is also dull but not stony)
Reduced or absent breath sounds and reduced vocal fremitus
Bronchial breathing at the upper fluid border — compressive atelectasis above the effusion can cause this
Tracheal deviation away from the effusion — with massive unilateral effusions only
Assess for heart failure signs (elevated JVP, displaced cardiac apex, S3 gallop, peripheral oedema), hepatic disease (ascites, spider naevi), and lymphadenopathy (supraclavicular, axillary — malignancy)

Initial investigation in general practice

Chest X-ray — posteroanterior and lateral views. Small effusions under 200 mL may not be visible on a PA film; the lateral view detects smaller volumes. Blunting of the costophrenic angle is the classic early sign; massive effusions produce a white-out with mediastinal shift to the opposite side.

Thoracic ultrasound (POCUS) — more sensitive than chest X-ray, detecting effusions from as little as 50 mL. It distinguishes free-flowing from loculated fluid, identifies septations (suggesting complex parapneumonic or empyema), and guides safe thoracentesis. MBS 55054 covers thoracic ultrasound. Point-of-care ultrasound is increasingly available in Australian general practice and emergency settings; if not available in-clinic, refer for ultrasound-guided assessment rather than proceeding blind.

CT chest with contrast — indicated for any new unexplained effusion. It identifies consolidation, mass, pleural thickening, lymphadenopathy, pulmonary embolism, and pleural plaques; characterises the pleura (pleural enhancement suggests exudate and inflammatory process); and is the essential staging tool for suspected malignancy or mesothelioma. Billed under MBS 56301.

Blood tests — FBC, urea and electrolytes, liver function, CRP, albumin, NT-proBNP (elevated with high sensitivity and specificity in cardiac cause), autoimmune markers (ANA, RF, ANCA) when connective tissue disease is suspected.

When to refer for thoracentesis

A diagnostic pleural tap is indicated for any new effusion of unclear cause. The one exception: a small bilateral transudate in a patient with known decompensated heart failure that resolves rapidly with diuresis can be observed without tapping — with a low threshold to revisit if the effusion is unilateral, persists despite treatment, or has atypical features.

Diagnostic thoracentesis (MBS 38812) is a specialist procedure. Refer to respiratory medicine, general medicine, or oncology depending on suspected cause.

B. Diagnosing the cause — Light’s criteria and pleural fluid analysis

Light’s criteria classify pleural fluid as exudate if any one of the following is met:

Pleural protein / serum protein > 0.5
Pleural LDH / serum LDH > 0.6
Pleural LDH > two-thirds the upper limit of normal serum LDH

Sensitivity for exudate is approximately 99%, but around 25% of true transudates are misclassified as exudates — particularly in patients with heart failure treated with diuretics, who concentrate pleural protein relatively. The serum-pleural albumin gradient corrects for this: a gradient above 12 g/L identifies a true transudate even when Light’s criteria suggest exudate.

What to send from the pleural fluid sample

Biochemistry — protein, LDH, glucose, pH (heparinised syringe on ice, analysed within one hour; pH below 7.2 with glucose below 2.2 mmol/L indicates empyema requiring drainage), amylase (elevated in pancreatitis and oesophageal rupture), triglycerides and cholesterol (suspected chylothorax)
Microbiology — Gram stain and culture, AFB smear and mycobacterial culture, fungal culture
Cytology — single-sample sensitivity for malignancy approximately 60%; higher with larger volume and repeat samples
Cell count and differential — neutrophil predominance (acute parapneumonic), lymphocyte predominance (TB, malignancy, chronic effusion), eosinophilia (pulmonary embolism, drug-induced, post-cardiac surgery, parasitic)
Adenosine deaminase (ADA) — elevated above 40 U/L is around 90% sensitive and specific for tuberculous pleuritis; particularly useful in patients from TB-endemic regions
NT-proBNP — very high pleural NT-proBNP confirms cardiac origin when Light’s criteria are borderline

A practical decision framework

Finding	Suggests
Bilateral transudate	Heart failure, cirrhosis, nephrotic syndrome, hypoalbuminaemia
Unilateral exudate + fever + neutrophilia	Parapneumonic effusion / empyema
Unilateral exudate + lymphocytosis + weight loss	Malignancy or tuberculosis
Haemorrhagic exudate + pleuritic chest pain	Pulmonary embolism, malignancy, haemothorax
pH < 7.2 + glucose < 2.2 mmol/L	Empyema — drainage required
High amylase + epigastric pain	Pancreatitis or oesophageal rupture
Triglycerides > 1.24 mmol/L	Chylothorax (thoracic duct injury, lymphoma)
Unilateral exudate + asbestos exposure	Mesothelioma until excluded

C. Treatment — draining, managing, and planning long-term care

Treating the underlying cause

Most of the management work is done by addressing the cause:

Heart failure — diuresis, ACE inhibitor or ARNi, beta-blocker, MRA, SGLT2 inhibitor per eTG Cardiovascular; therapeutic thoracentesis if symptomatic despite diuresis
Pneumonia / parapneumonic effusion — antibiotics per eTG Respiratory; chest drain if complicated parapneumonic (pH below 7.2, positive Gram stain, glucose below 2.2 mmol/L, or frank pus)
Cirrhosis with hepatic hydrothorax — sodium restriction and diuretics; TIPS referral for refractory cases
Connective tissue disease — disease-modifying therapy (RA and SLE protocols)
Drug-induced — identify and withdraw the causative agent (amiodarone, methotrexate, nitrofurantoin, dasatinib); effusion typically resolves over weeks
Pulmonary embolism — anticoagulation; haemorrhagic exudate usually resolves without drainage
Chylothorax — fasting and medium-chain triglyceride diet; specialist surgical ligation of the thoracic duct if persistent

Therapeutic drainage

Drainage for symptom relief is indicated when large effusions cause significant dyspnoea not adequately managed by treating the cause. The critical safety rule: limit any single tap to 1,500 mL to avoid re-expansion pulmonary oedema — a complication of rapid lung re-expansion that can cause severe hypoxia. Stop the procedure if chest pain, cough, or haemodynamic deterioration occurs.

Chest drain insertion (MBS 38818) under thoracic ultrasound guidance is standard for empyema and large symptomatic effusions requiring ongoing drainage.

Empyema management

Empyema with pH below 7.2, glucose below 2.2 mmol/L, positive Gram stain, or macroscopically frank pus requires a chest drain. For thick or loculated empyema where simple drainage is insufficient, the MIST-2 trial (Rahman NEJM 2011) established that intrapleural tissue plasminogen activator (tPA) plus DNase administered through the drain significantly reduces the need for surgical referral — now standard practice per BTS 2023 Pleural Disease Guidelines. Unresolved or organising empyema is managed by video-assisted thoracoscopic surgery (VATS) decortication at a thoracic surgery centre.

Recurrent malignant effusion

For effusions that recur rapidly after drainage in patients with malignancy, guidelines support two main options:

Indwelling pleural catheter (IPC) — a soft silicone catheter placed under local anaesthesia, allowing home drainage two to three times weekly by the patient or a district nurse. The TIME-2 trial (Davies JAMA 2012) showed IPC was non-inferior to talc pleurodesis for symptom control with a shorter initial hospital stay. IPC is now the preferred approach for most patients with recurrent malignant effusion.
Chemical pleurodesis — talc instillation via chest drain or thoracoscopy; effective in approximately 70% of cases; suitable when home IPC management is not practical.

Mesothelioma — diagnosis, treatment, and compensation

Australia has one of the world’s highest historical rates of mesothelioma because of occupational asbestos exposure in mining (Wittenoom, WA), construction, shipbuilding, and industrial settings. Around 700 new cases occur annually. Latency from exposure to diagnosis is typically 20–50 years, meaning many patients are now presenting decades after their working-age exposure.

Any unilateral exudative effusion in a patient with asbestos exposure history — even remote occupational exposure — requires expedited CT chest and specialist referral for tissue biopsy. Mesothelioma is managed by dedicated multidisciplinary teams at quaternary centres: Royal Prince Alfred (Sydney), Princess Alexandra (Brisbane), Sir Charles Gairdner (Perth), Royal Adelaide Hospital, and Peter MacCallum Cancer Centre (Melbourne).

Workers’ compensation is a parallel pathway that GPs must initiate alongside treatment. Document the full occupational history carefully. State asbestos disease compensation schemes vary:

NSW: Dust Diseases Tribunal
VIC: WorkSafe VIC asbestos diseases
QLD: WorkCover Queensland
WA: WorkCover WA
SA: ReturnToWorkSA
TAS: WorkCover Tasmania

The Bernie Banton Foundation provides advocacy support and legal referral for patients and families.

D. Australian operations

Key MBS items

MBS 58503 — chest X-ray (in-clinic or radiology)
MBS 55054 — thoracic ultrasound
MBS 56301 — CT chest
MBS 38812 / 38815 — diagnostic and therapeutic thoracentesis (specialist)
MBS 38818 / 38819 — chest drain insertion
MBS 30614 / 30615 — VATS procedures
MBS 707 / 715 — chronic disease and 75+ health assessments — appropriate context for identifying and investigating unexplained effusion in older patients

PBS medicines

Antibiotics for parapneumonic effusion and empyema are prescribed per eTG Respiratory protocols. Anti-tuberculous therapy (isoniazid, rifampicin, pyrazinamide, ethambutol — RIPE regimen) is available on the PBS under Authority for TB. Chemotherapy for mesothelioma (pemetrexed plus cisplatin or carboplatin, Section 100) and immunotherapy (nivolumab plus ipilimumab, Authority) are PBS-listed for mesothelioma. Diuretics for cardiac transudates are on the General Schedule.

Notification requirements

Tuberculosis is nationally notifiable in all Australian states and territories — notify the state health department upon clinical suspicion, before culture confirmation. Mesothelioma is notifiable to state cancer registries. Asbestos-related disease activates workers’ compensation reporting obligations; document the diagnosis promptly.

E. Special populations

Immunocompromised patients. Pleural infections in patients on immunosuppression, chemotherapy, or with HIV may present atypically — fever blunted, organisms unusual (fungal, mycobacterial, Nocardia). Thoracentesis and comprehensive culture including fungal and AFB are especially important. Early infectious diseases consultation is appropriate.

Patients from TB-endemic regions. Tuberculous pleuritis is an important diagnosis in patients from South-East Asia, Sub-Saharan Africa, South Asia, and Pacific Island nations — communities well represented in Australian general practice. A unilateral lymphocyte-predominant exudate with elevated ADA above 40 U/L in this context has 90% sensitivity and specificity for TB. Mycobacterial culture is the confirmatory test, but treatment is often started before culture confirmation in high-probability cases in consultation with a TB physician or infectious diseases specialist.

Older adults. Heart failure dominates in older patients, but atypical unilateral or unexplained effusions still warrant investigation regardless of age. Falls risk from vasovagal events during thoracentesis — particularly in frail patients — is managed by performing drainage with the patient upright-sitting and observing for 30 minutes post-procedure.

Paediatric. Parapneumonic effusion from community-acquired pneumonia is the most common cause in children. Management follows paediatric respiratory guidelines; referral to a paediatric respiratory physician is appropriate for chest drain decisions, intrapleural fibrinolytic use, or surgical planning.

Pregnancy. New pleural effusion in pregnancy requires prompt investigation — causes include pre-eclampsia/HELLP syndrome (typically bilateral with other features of multi-system disease), peripartum cardiomyopathy, and infection. Management is coordinated with the maternal-foetal medicine team.

When to escalate

Refer urgently to the emergency department:

Suspected tension physiology: tachycardia, hypotension, tracheal deviation, respiratory distress, massive white-out on CXR
Suspected empyema — fever, raised inflammatory markers, pleural pH below 7.2 — requiring same-day drainage
Haemothorax — active haemorrhage into the pleural space requiring surgical assessment

Refer semi-urgently within 1–2 weeks to respiratory medicine or the relevant specialty:

Any new unilateral effusion of unclear cause
Bilateral effusion not clearly cardiac in origin or not resolving with appropriate treatment for the presumed cause
Suspected malignancy or mesothelioma — expedite CT and referral, particularly with asbestos exposure history
Any lymphocyte-predominant exudate (TB and malignancy must be excluded)
Recurrent effusion (two or more episodes) requiring long-term management planning

Include in the referral: chest X-ray and CT reports, blood results (FBC, liver function, renal function, NT-proBNP, CRP, albumin), detailed occupational and asbestos exposure history, current medications, and relevant comorbidities.

What this article is and is not

This is general health information drawn from current clinical guidance — Therapeutic Guidelines Respiratory, BTS 2023 Pleural Disease Guidelines, Lung Foundation Australia, and TSANZ. It is not personal medical advice and does not create a doctor–patient relationship. Decisions about investigation, drainage, biopsy, and specialist referral are made with your treating GP, respiratory physician, or thoracic surgeon.

For Australian consumer information: Lung Foundation Australia, HealthDirect, Better Health Channel. For mesothelioma support and legal guidance: Bernie Banton Foundation, Dust Diseases Tribunal NSW.

Sources cited

Frequently asked questions

What are the most common causes of a pleural effusion in Australia?

Heart failure is the single most common cause, accounting for around half of all effusions — usually presenting as a bilateral transudate with other signs of fluid overload. Parapneumonic effusion from community-acquired pneumonia is the second most common, presenting as a unilateral exudate with fever and productive cough. Malignancy — most often lung cancer, breast metastases, lymphoma, or mesothelioma — accounts for around 15% of effusions. Mesothelioma is a particular Australian concern given high historical rates of occupational asbestos exposure in mining, construction, and shipbuilding industries.
What is Light's criteria and why does it matter?

Light's criteria, established in 1972 and still the international standard, classify pleural fluid as an exudate if any one of three conditions is met: pleural protein divided by serum protein is greater than 0.5; pleural LDH divided by serum LDH is greater than 0.6; or pleural LDH is above two-thirds the upper limit of normal serum LDH. Exudate means there is an inflammatory, neoplastic, or lymphatic process driving fluid accumulation — requiring specific investigation. Transudate means a pressure or oncotic cause — often manageable without diagnostic tapping if the clinical cause is clear.
When does a pleural effusion need draining?

A therapeutic drain is indicated when a large effusion causes significant breathlessness that is not responding to treating the underlying cause. Drainage is also required for empyema — infected pleural fluid with pH below 7.2, glucose below 2.2 mmol/L, or positive Gram stain — which needs a chest drain as soon as it is confirmed. Recurrent malignant effusions that keep coming back are managed with an indwelling pleural catheter (a soft tube allowing home drainage two to three times weekly) or chemical pleurodesis. A single therapeutic tap is limited to 1,500 mL to avoid re-expansion pulmonary oedema.
What should I do if I find an effusion in a patient with asbestos exposure history?

Treat it as potentially mesothelioma until proven otherwise, regardless of how long ago the exposure was — mesothelioma has a latency of 20–50 years from asbestos exposure. Order urgent CT chest with contrast and refer to a respiratory physician or mesothelioma multidisciplinary team. Tissue biopsy (CT-guided pleural biopsy or thoracoscopy) confirms the diagnosis. Simultaneously, document the occupational history carefully and make a warm referral to the state asbestos disease compensation scheme — NSW Dust Diseases Tribunal, WorkSafe VIC, WorkCover Queensland, or equivalent — because compensation claims require early documentation.
Can tuberculosis cause a pleural effusion and how is it diagnosed?

Yes. Tuberculous pleuritis is an important cause of unilateral lymphocyte-predominant exudative effusion, particularly in patients from TB-endemic countries — a common presentation in Australian general practice given our migrant population from South-East Asia, Sub-Saharan Africa, South Asia, and Pacific Island nations. Standard AFB smear has low sensitivity in pleural fluid. The adenosine deaminase (ADA) level elevated above 40 U/L in a lymphocyte-predominant exudate is 90% sensitive and specific for TB pleuritis. Mycobacterial culture takes 6–8 weeks; pleural biopsy provides the highest diagnostic yield. Notification to the state TB program is mandatory on diagnosis.

Source quality

Sources grouped by evidence tier. AU primary tier first; international where AU is silent or lagging; named-author reconstruction where guidelines have not yet caught up. How tiers work.