Quick answer. A pleural effusion is a build-up of fluid in the space between the lung and the chest wall, often caused by heart failure, infection or cancer; it can cause breathlessness and chest discomfort and is investigated and treated by draining the fluid (a pleural tap) and addressing the underlying cause.
A pleural effusion is an abnormal collection of fluid in the pleural space – the thin gap between the lung and the inside of the chest wall. A small amount of fluid is normally present to help the lungs move smoothly, but when too much accumulates, it presses on the lung and makes breathing harder.
Pleural effusion is not a disease in itself but a sign of an underlying problem. Finding and treating the cause is just as important as removing the fluid.
At a glance
| Type | Typical causes | Notes |
|---|---|---|
| Transudate (watery) | Heart failure, liver or kidney disease | Often from fluid balance problems |
| Exudate (protein-rich) | Infection (pneumonia), cancer, tuberculosis | Suggests inflammation or local disease |
| Infected fluid (empyema) | Pneumonia, chest infection | Pus in the pleural space; needs drainage |
| Blood (haemothorax) | Trauma, after surgery, some cancers | Requires urgent assessment |
What a pleural effusion is
The pleura is a double-layered membrane: one layer lines the lung and the other lines the chest wall, with a small amount of lubricating fluid in between. When the balance of fluid production and drainage is disturbed – by raised pressure in blood vessels, leaky inflamed membranes, infection or a blockage of lymph drainage – fluid builds up and compresses the lung.
Effusions are broadly divided into transudates (thin, watery fluid, usually from heart, liver or kidney problems) and exudates (protein-rich fluid from inflammation, infection or cancer). This distinction helps doctors find the cause.
Common causes
- Heart failure – one of the most common causes
- Infection – pneumonia, which may lead to infected fluid (empyema), and tuberculosis
- Cancer – lung cancer, breast cancer or spread of other cancers to the pleura
- Liver disease and kidney disease
- Pulmonary embolism
- Conditions affecting the lining, such as some autoimmune diseases
Symptoms
- Breathlessness, especially when lying flat or on exertion
- Chest discomfort or a heavy, tight feeling, sometimes worse on breathing in
- A dry cough
- Symptoms of the underlying cause – for example fever with infection, or leg swelling with heart failure
Small effusions may cause no symptoms and are sometimes found by chance on a chest X-ray. Larger effusions tend to cause more breathlessness.
How it is diagnosed
A chest X-ray usually shows the fluid, and an ultrasound or CT scan gives more detail and helps guide drainage. A key test is a pleural tap (pleural aspiration / thoracentesis), where a doctor uses a thin needle, often with ultrasound guidance, to remove a sample of fluid. The fluid is analysed in the laboratory to determine whether it is a transudate or exudate and to look for infection, cancer cells or TB.
Treatment: drainage and treating the cause
If the effusion is causing breathlessness, fluid can be drained to relieve symptoms – either by a therapeutic pleural tap or by inserting a chest tube (chest drain) for larger or infected collections. Infected fluid (empyema) usually needs drainage along with antibiotics.
At the same time, the underlying cause is treated – for example, medications and fluid management for heart failure, antibiotics for infection, or cancer-directed treatment. For recurrent effusions due to cancer, options such as a long-term indwelling pleural catheter or a procedure to seal the pleural space (pleurodesis) may be considered.
When to seek care
See a doctor if you have unexplained or worsening breathlessness, persistent chest discomfort, or a cough that does not settle. Seek urgent or emergency care if you have severe or rapidly worsening breathlessness, chest pain, a high fever with feeling very unwell, or you cough up blood. In an emergency, go to the nearest Emergency Department or call 995.
Because pleural effusion is a sign of another condition, a respiratory physician will investigate the cause so the right treatment can be given.
How to prepare for a pleural tap
If your doctor recommends a pleural tap (thoracentesis), there are a few simple things that help the procedure go smoothly. Tell the team about any blood-thinning or anti-platelet medicines you take, such as warfarin, aspirin, clopidogrel or a direct oral anticoagulant, because these may need to be paused beforehand. Mention any bleeding tendency, recent fever, or allergies to local anaesthetic. You can usually eat and drink as normal, and you do not generally need to stop driving beforehand, but check with your clinic.
During the procedure you will typically sit upright and lean forward over a pillow or table. After cleaning and numbing the skin, the doctor inserts a thin needle, often under ultrasound guidance, to draw off fluid. You may feel pressure or a brief cough as the lung re-expands. A small effusion sample is sent to the laboratory; if drainage is for symptom relief, more fluid may be removed. Most taps take 15 to 30 minutes.
What to expect afterwards
After a tap you may have mild soreness at the puncture site for a day or two, which usually settles with simple pain relief. Many clinics arrange a chest X-ray afterwards to check the lung and rule out a small air leak (pneumothorax). Seek prompt review if you develop increasing breathlessness, sharp chest pain, fever, or bleeding from the site. Because an effusion can re-accumulate, follow-up is arranged to monitor for fluid returning and to continue treating the underlying cause.
Costs and subsidies in Singapore
Costs vary widely depending on whether the effusion is investigated as an outpatient or during a hospital admission, the imaging needed, and whether a chest drain or further procedures are required. In public hospitals and polyclinics, subsidised rates apply for eligible Singapore Citizens and Permanent Residents, and an inpatient stay for drainage may be claimable under MediShield Life and, where applicable, MediSave. A medical social worker can advise on means-tested assistance if cost is a concern. Ask the clinic for an estimate before planned procedures, as charges differ between providers.
Questions to ask your doctor
- What is the most likely cause of my effusion, and what did the fluid analysis show?
- Do I need the fluid drained now, and is a chest drain likely to be required?
- How will the underlying cause be treated and monitored?
- Is the effusion likely to come back, and what are the options if it does?
- What symptoms should prompt me to return urgently?
Common questions
Is a pleural tap painful?
The skin is numbed with local anaesthetic, so most people feel pressure rather than sharp pain. Some discomfort or a brief cough as the lung re-expands is normal.
Can a pleural effusion go away on its own?
Small effusions sometimes resolve once the underlying cause, such as heart failure or a chest infection, is treated. Larger or persistent effusions usually need drainage and ongoing treatment of the cause.
Does fluid always mean cancer?
No. There are many causes, including heart failure and infection. The fluid analysis and other tests help your doctor identify the specific cause.
Related guides
- Best Respiratory & Lung Clinics in Singapore — our editorial shortlist
- Tuberculosis (TB)
- Bronchiectasis
- Pulmonary Embolism
Sources
- SingHealth – Pleural Effusion
- HealthHub – Health Conditions A-Z
- Ng Teng Fong General Hospital – Respiratory Medicine
- Mount Elizabeth – Respiratory (Pulmonary) Medicine
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