Pleural effusion
Ultrasound before every tap. Then decide: transudate or exudate, infected or not, and is it TB or cancer?
A 34-year-old woman from a rural area has 6 weeks of fever, night sweats, dry cough and 5 kg weight loss. Chest X-ray shows a moderate left pleural effusion. Her ultrasound-guided tap shows straw-coloured fluid: protein 5.2 g/dL (serum 7.0), LDH 480 U/L (serum 220, upper normal 250), glucose 55 mg/dL (3.1 mmol/L), lymphocytes 85%, pH 7.35, ADA 72 U/L. AFB smear negative.
Transudate or exudate, what is the likely cause, and how do you confirm and treat it?
- Breathless or hypoxicOxygen to target, sit up, drain some fluid for relief.
- Fever with effusion after pneumoniaTap and check pH: empyema needs a drain.
- UltrasoundConfirms fluid, shows loculations, guides the tap.
- Diagnostic tap if cause not obviousSend paired serum protein and LDH at the same time.
- Apply Light's criteriaTransudate or exudate.
- Bilateral with heart failureUsually transudate: treat the heart failure, tap only if atypical.
- Find the causeTB, cancer, infection, heart, liver, kidneys, PE.
- Chest teamRecurrent, unexplained or malignant effusions.
- Fever with effusion and sepsis
- Pleural pH below 7.2 or pus
- Blood on tap in trauma or anticoagulated patient
- Massive effusion with mediastinal shift
- Breathless or hypoxic
- Empyema
- Tuberculous effusion
- Malignant effusion
- Haemothorax
- Pulmonary embolism
- Re-expansion pulmonary oedema after drainage
| Exudate (Light's) | Fluid protein ÷ serum protein above 0.5, or fluid LDH ÷ serum LDH above 0.6, or fluid LDH above two-thirds of the upper normal serum LDH |
| Drain needed | pH below 7.2, pus, or organisms on Gram stain |
| TB effusion | Lymphocytes, high ADA (above about 40 U/L), common in Pakistan |
| Haemothorax | Fluid haematocrit above half the blood haematocrit |
| Therapeutic aspiration | Usually no more than 1.5 L at one time |
| Lidocaine 1% | Up to 3 mg/kg (about 20 mL for 70 kg) |
Check every dose against a current drug reference and your hospital protocol.
On this page
What is a pleural effusion?
Fluid between the lung and chest wall. Transudates come from pressure or protein imbalance (heart failure, cirrhosis, nephrotic syndrome). Exudates come from inflamed or leaky pleura (infection, TB, cancer, PE). In Pakistan, tuberculosis is a leading cause in young adults; parapneumonic effusion, heart failure, cancer and liver disease are common in older patients.
Presentation
- Breathlessness, dry cough, pleuritic chest pain.
- Fever, night sweats and weight loss suggest TB or cancer.
- Orthopnoea and swollen legs suggest heart failure.
- Fever after a pneumonia that isn't settling suggests empyema.
Examination
- Reduced expansion, stony dull percussion, reduced breath sounds and vocal resonance on the affected side.
- Trachea pushed away in a large effusion.
- Look for the cause: raised JVP, ascites, lymph nodes, clubbing, breast lump, leg swelling, signs of liver disease.
Transudate or exudate?
- Heart failure
- Cirrhosis
- Nephrotic syndrome
- Low albumin
- Hypothyroidism
- Peritoneal dialysis
- Pneumonia and empyema
- TB
- Cancer
- PE
- Rheumatoid, lupus
- Pancreatitis
- Drugs
Send a serum protein and LDH at the same time as the tap. Without them you can't apply Light's criteria.
What the fluid tells you
| Finding | Suggests |
|---|---|
| pH below 7.2, pus, organisms | Complicated parapneumonic effusion or empyema: chest drain |
| Lymphocytes, high ADA, low glucose | Tuberculosis |
| Blood-stained | Cancer, PE, trauma |
| Fluid haematocrit above half the blood's | Haemothorax |
| Malignant cells | Cancer (cytology positive in about half; repeat if suspicion high) |
| Milky, high triglycerides | Chylothorax |
| High amylase | Pancreatitis, oesophageal rupture |
| Low glucose | Infection, TB, rheumatoid, cancer |
The tap
- UltrasoundMark or guide the site; blind taps cause pneumothorax and organ injury.
- PositionSitting, leaning forward over a table.
- SitePosterior chest, below the top of the fluid, above the upper border of a rib.
- Local anaestheticLidocaine 1%, aspirate before injecting.
- Sample50–60 mL: protein, LDH, glucose, pH (blood gas analyser), cells, Gram stain, culture, AFB, GeneXpert, cytology, ADA.
See pleural aspiration for the procedure in detail.
Treat the cause
| Cause | Treatment |
|---|---|
| Heart failure | Diuretics; tap only if one-sided, painful, febrile or not responding |
| Parapneumonic | Antibiotics; chest drain if pH below 7.2, pus or positive Gram stain |
| Empyema | Chest drain, antibiotics for weeks, sometimes surgery |
| Tuberculous | Standard anti-TB treatment; therapeutic tapping if breathless |
| Malignant | Drain for relief, then pleurodesis or indwelling pleural catheter; oncology |
| Haemothorax | Large-bore drain, resuscitate, cardiothoracic opinion |
| PE | Anticoagulation |
TB effusion in Pakistan
- A common cause of a one-sided exudate in young adults.
- Fluid: lymphocytes, high protein, high ADA, often low glucose. AFB smear and culture are usually negative.
- Pleural biopsy (or GeneXpert on fluid, which has low sensitivity) can confirm.
- Treat with standard anti-TB drugs through the national TB programme; refer contacts for screening.
Treatment doses
Remove no more than about 1.5 litres at one time. Draining quickly can cause re-expansion pulmonary oedema: cough, chest tightness and low oxygen. Stop if symptoms appear.
Common mistakes
- Tapping without paired serum protein and LDH.
- Blind taps without ultrasound.
- Treating an empyema with antibiotics alone.
- Not checking pleural pH in an infected-looking effusion.
- Draining 3 litres in one go.
- Tapping bilateral effusions in clear heart failure.
Follow-up
- Repeat chest X-ray after drainage.
- TB effusions: monitor on treatment; contact screening.
- Recurrent effusion with no cause found: refer for thoracoscopy.
Frequently asked questions
What are Light's criteria?
An effusion is an exudate if fluid protein divided by serum protein is above 0.5, fluid LDH divided by serum LDH is above 0.6, or fluid LDH is above two-thirds of the upper normal serum LDH.
How is a tuberculous pleural effusion diagnosed?
A lymphocyte-rich exudate with high ADA, often with low glucose. AFB smear is usually negative, so pleural biopsy or GeneXpert can help confirm it.
How much fluid can be drained at once?
Up to about 1.5 litres, stopping earlier if the patient coughs or feels chest tightness.
When does a pleural effusion need a chest drain?
When infected (pus, pH below 7.2, organisms on Gram stain), for haemothorax, and for large symptomatic effusions.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A pleural fluid protein ratio is 0.7. What does this mean?
Answer: Exudate. Light's criteria: protein ratio above 0.5 indicates an exudate.
- Chylothorax: Needs triglycerides.
- Transudate: Ratio above 0.5 is exudate.
- Normal fluid: No.
- Empyema definitely: Not by itself.
2. A young man has a lymphocytic exudate with ADA 72 U/L. What is the likely cause?
Answer: Tuberculous effusion. Lymphocytes with high ADA strongly suggest TB in Pakistan.
- Empyema: Neutrophils, low pH.
- Nephrotic syndrome: Transudate.
- Cirrhosis: Transudate.
- Heart failure: Would be a transudate.
3. A parapneumonic effusion has pH 7.0. What is needed?
Answer: Chest drain. Complicated parapneumonic effusion or empyema needs drainage.
- Furosemide: No.
- Repeat X-ray in 2 weeks: Delay.
- Pleurodesis: Not now.
- Antibiotics only: pH below 7.2 needs drainage.
4. A pleural tap shows fluid protein 38 g/L (serum 60), fluid LDH 400 U/L (serum upper limit 250), lymphocyte-rich, ADA 70 U/L. What is the most likely cause in Pakistan?
Answer: Tuberculous effusion. Light’s criteria (exudate if any): fluid:serum protein > 0.5, fluid:serum LDH > 0.6, fluid LDH > ⅔ of upper limit of normal serum LDH. Here protein ratio 0.63 and LDH > 167 → exudate. Lymphocytic exudate with high ADA (> 40) strongly suggests TB; pleural biopsy confirms. Causes of exudate: TB, parapneumonic, malignancy, PE, RA. Transudates: heart failure, cirrhosis, nephrotic syndrome, hypothyroidism.
- Congestive heart failure: Heart failure causes a transudate.
- Hepatic hydrothorax: Hepatic hydrothorax is a transudate.
- Nephrotic syndrome: Nephrotic syndrome causes a transudate.
5. A 25-year-old man from Swat has fever, night sweats and a right pleural effusion. Pleural fluid: protein 52 g/L (serum 70 g/L), lymphocytes 90%, adenosine deaminase raised, no malignant cells. What is the most likely cause?
Answer: Tuberculous pleurisy. Pleural fluid protein ÷ serum protein > 0.5 makes this an exudate (Light’s criteria). A lymphocyte-rich exudate with a high adenosine deaminase in a young person in a high-burden country strongly suggests TB. Pleural biopsy (granulomas, culture) confirms it. Treat with standard anti-TB therapy.
- Congestive heart failure: Heart failure causes a transudate (protein < 30 g/L).
- Parapneumonic effusion: Parapneumonic effusions are neutrophil-predominant with a recent pneumonia; 90% lymphocytes with high ADA points to TB.
- Nephrotic syndrome: Nephrotic syndrome causes a transudate.
6. At which rib level does the lower border of the parietal pleura cross the mid-axillary line?
Answer: 10th rib. Remember 6–8–10–12: the lungs' lower border lies at the 6th rib (mid-clavicular), 8th (mid-axillary) and 10th (posteriorly); the pleura is two ribs lower: 8th, 10th and 12th. The space between them is the costodiaphragmatic recess, where fluid collects and where pleural taps are done.
- 6th rib: Lung at the mid-clavicular line.
- 8th rib: Lung border at the mid-axillary line.
- 12th rib: Pleura posteriorly near the vertebrae.
- 4th rib: Not correct.
7. Where does the thoracic duct end?
Answer: Left jugulosubclavian junction. The thoracic duct starts at the cisterna chyli (L1–L2), passes through the aortic hiatus, ascends behind the oesophagus, crosses to the left at T4/5, and empties into the left venous angle (left IJV–subclavian junction). It drains lymph from everything except the right upper body (right lymphatic duct). Injury causes chylothorax.
- Right atrium: Not correct.
- Azygos vein: Runs beside it but does not drain into it.
- Right subclavian vein: The right lymphatic duct drains there.
- Superior vena cava directly: Not correct.
References and dose sources
- BTS pleural 2023
- Lidocaine (lignocaine) dosing: Drugs.com: Lidocaine dosage (see also our lidocaine (lignocaine) dose page)
- Co-amoxiclav (amoxicillin with clavulanic acid) dosing: Drugs.com: Amoxicillin/clavulanate dosage (see also our co-amoxiclav (amoxicillin with clavulanic acid) dose page)
- Furosemide dosing: Drugs.com: Furosemide dosage (see also our furosemide dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.