50-100 mL of pleural fluid, typically collected in 4-5 tubes
- Lavender top tube (for cell count and differential; 10 mL)
- Green top tube (for chemistry; 10 mL)
- Sterile containers or special vials (for microbiology, Gram stain, and AFB stain; 10-20 mL)
- Clear container with fixative (for cytology; 20-30 mL)
If indicated; may also consider drawing blood cultures and 5-10 mL of venous blood in red or tiger top tube (for total protein, LDH, cholesterol, bilirubin, or other testing as indicated)
Additional information
- Aspiration is done very cautiously in patients with bleeding tendencies, on anticoagulant therapy, and patients with unstable vital signs
- Record exact location from which fluid was removed and label specimen container on lab request
- Send specimen to lab immediately
Pleural fluid aspiration procedure (diagnostic thoracentesis)
- Consent patient for procedure
- Chest X-ray, ultrasound or CT guidance is commonly used to locate an appropriate site for aspiration
- Record baseline vital signs and continuously monitor cardiac rhythm and pulse oximetry
- Patient is instructed to sit in 45-degree sitting position with arms forward supported on table/pillows
- Posterior or axillary approach is preferable if the effusion is large; otherwise, CT or Ultrasound guidance should be considered
- Locate the appropriate site for aspiration, mark this, sterilize the skin with chlorhexidine or betadine and use sterile technique thereafter
- Using a small gauge needle, infiltrate local anesthetic (e.g. 1% lidocaine) one rib space below the upper level the effusion (area of dullness on percussion or per imaging study)
- Advise the patient not to cough, breathe deeply, or move suddenly during procedure
- Carefully insert the appropriate (18-20 G) needle attached to a 5 mL or larger syringe and the catheter device, through the anaesthetized skin, directly above the rib, with a slightly inferior directed angle, while aspirating on the syringe (Note: ensure needle enters immediately above rib to avoid the neurovascular bundle)
- A 50-ml syringe is attached and 3-way stopcock and clamps are opened on tubing to aspirate fluid. If no fluid is aspirated then try adjusting the angle of needle or advancing/adjusting the depth and angle of the plastic catheter (most kits for thoracentesis have a needle that is removed once successful aspiration of fluid is achieved, with a plastic catheter remaining, though which continued aspiration of fluid is performed)
- During aspiration, observe patient for signs of respiratory distress, such as weakness, dyspnea, pallor, cyanosis, changes in heart rate, tachypnea, diaphoresis, blood-tinged frothy mucus, and hypotension
- Remove needle and/or plastic catheter and apply sterile dressing
- Post-aspiration chest X-ray is recommended (to make sure a pneumothorax has not occurred from the procedure)
- Pleural fluid analysis (cells/culture) is performed to detect and estimate the cell count, differential count, and isolate and identify microorganisms from the pleural fluid
- The pleural cavity and organs within it are lined with a protective pleural membrane. The pleural space (e.g. between the membranes) normally contain just a few mL of serous fluid
- The various mechanisms of pleural fluid accumulation include:
- Increased interstitial fluid in the lungs secondary to increased pulmonary capillary pressure (heart failure)
- Increased permeability (pneumonia and pulmonary embolism)
- Decreased intrapleural pressure (atelectasis)
- Decreased plasma oncotic pressure (hypoalbuminemia)
- Increased pleural membrane permeability and obstructed lymphatic flow (pleural malignancy or infection)
- Diaphragmatic defects (hepatic hydrothorax)
- Thoracic duct rupture (chylothorax)
- Alteration of one or more of these factors maintaining the balance, results in pleural effusions, which may be transudative or exudative effusions
- Transudative effusion is usually due to increased hydrostatic pressure and/or decreased osmotic pressure
- Exudative effusion results from increased vascular permeability and a shift of fluid from the pulmonary interstitium due to injury of the pleura or subpleural lung parenchyma
- The clinical utility of pleural fluid analysis for cell count, culture, and cytology include:
- To evaluate and determine the cause and nature of pleural effusion
- To distinguish between transudate and exudate
- To aid in the diagnosis of immune diseases, malignancy, or infection
- To permit better radiographic visualization of the lung when large effusions are present
- Classic signs and symptoms of pleural effusion may be observed, usually once the effusion volume is >300 mL
- Symptoms/Signs of pleural effusion may include (depends upon the cause):
- Fever
- Hemoptysis
- Breath sounds (Diminished)
- Chest pain (Often pleuritic)
- Chest pressure
- Cough
- Dyspnea
- Percussion (Dullness to)
- Pleural friction rub
- Reduced tactile and vocal fremitus
- Weight loss
- Various combinations of tests have been used to classify an effusion as transudate or exudate. This is the initial step in determining the etiology of a pleural effusion
Characteristics/test Transudate Exudate Appearance Clear Cloudy or turbid Specific gravity <1.015 >1.015 Total protein <2.5 g/dL >3.0 g/dL WBC count <100 WBC/mm3 >1000 WBC/mm3 Fluid protein/serum
protein ratio<0.5 >0.5 Lactate dehydrogenase
(LDH)Parallels serum value >200 U/L Fluid LDH/serum LDH ratio <0.6 >0.6 Fluid cholesterol <55 (45-60) mg/dL >55 (45-60) mg/dL Fluid cholesterol/serum
cholesterol ratio
0.3>0.3 Fluid bilirubin/serum
bilirubin ratio0.6>0.6 Albumin gradient
(serum albumin
minus pleural
fluid albumin)>1.2 g/dL 1.2 g/dL
Overview on appearance and specific gravity
- Normally pleural fluid appears clear and straw colored that may vary in different conditions such as:
Appearance Suspected
condition/significanceClear, straw-colored Transudate Cloudy or turbid Exudate Cloudy, purulent Empyema Red tinge or bloody Traumatic tap, malignancy,
trauma, pulmonary
infarction or embolusGreen-white, turbid Rheumatoid pleurisy Milky-white or yellow-bloody Chylous as in lymphoma,
trauma to thoracic
duct, yellow nail syndrome,
lymphangioleiomyomatosisMilky or green, metallic sheen Pseudochylous as in
tuberculosis or rheumatoid
pleuritis, trapped lungViscous, hemorrhagic or
clearMesothelioma Anchovy-paste color Rupture of amebic liver
abscess - A traumatic tap will usually become progressively less bloodstained as aspiration continues
- The causes of milky appearance of pleural fluid include:
- Chylothorax
- Very high number of leukocytes
- Increased cholesterol
- Pseudochylous effusions can be due to chronic effusion caused by tuberculosis or rheumatoid arthritis
- Measurement of specific gravity by refractometer often gives false high results, thereby should be interpreted with caution along with other test results
Overview on cell count and differential
- >100,000 RBCs/mm3 is indicative of conditions, which include:
- Trauma
- Malignancy
- Pulmonary embolism
- Post-cardiac injury syndrome
- Asbestos pleurisy
- Nonuniform color during aspiration, fluid clotting within minutes, and the absence of hemosiderin laden macrophages is suggestive of traumatic thoracentesis
- There is significant overlap between diseases associated with elevated total WBC count such as:
WBC count Suspected
condition/significance<1000/mm3 Usually Transudates <5000/mm3 Chronic exudates,
malignancy, tuberculosis>10,000/mm3 Parapneumonic effusions,
pancreatitis, postcardiac injury,
pulmonary infarction,
acute asbestos pleurisy>50,000/mm3 Parapneumonic effusions
(empyema / pneumonia related) - When pleural fluid is grossly purulent, WBC count may be less than expected value due to WBC lyses
- Polymorphonuclear (PMN) predominance is suggestive of diseases that tend to present early such as bacterial pneumonia, pulmonary embolism, pulmonary infarction, and pancreatitis
- Lymphocytic predominance, often 85-90% of the total cells is seen in chronic conditions such as tuberculosis, lymphoma, sarcoidosis, rheumatoid pleurisy, and carcinoma
- Elevated pleural fluid eosinophils (>10% of total) is usually seen in pneumothorax and certain infections, benign asbestosis, parasitic infections, hydropneumothorax
- Mesothelial cells predominate in transudates and in conditions such as empyema, rheumatoid pleurisy, chronic malignant effusions, and following the use of sclerosing agents, but is absent in tuberculosis
- Benign mesothelial cells should be differentiated from malignant cells as in mesothelioma and metastatic adenocarcinoma and also from macrophages
Overview on culture
- Bacterial, fungal, mycobacterial, viral cultures, Gram stain, KOH and AFB stains are performed to evaluate for infection
- The most common infectious cause of pleural effusion is a due to bacterial pneumonia that may lead to parapneumonic effusion if left untreated
- Parapneumonic effusion occurs most often due to bacterial causes and to a lesser extent by fungal and other causes
- Cultures are usually positive during early stages of the infection, however antibiotic therapy may produce negative culture despite positive Gram's stain and grossly purulent fluid
Overview on cytology
- Pleural effusion is usually the first manifestation of recurrent disease, malignancy, and often has prognostic significance (usually worse prognosis)
- Malignancy is probably the most common cause of exudative pleural effusions in patients over the age 60, especially carcinoma of lung and breast
- Malignancies commonly associated with pleural effusions include:
- Primary lung carcinoma
- Metastatic carcinoma
- Lymphoma
- Mesothelioma
- Repeated sampling increases the diagnostic rate of detecting malignancy
Pleural fluid profiles in various disease states:
Transudate
| Diagnosis | Congestive heart failure | Cirrhosis |
|---|---|---|
| Appearance | Clear, straw-colored | Clear, straw-colored |
| WBC's (cells/mm3 or /µL) and Differential | <1,000 | <500 |
| RBC's (cells/mm3 or /µL) | <1,000 | <1,000 |
| Bacteriologic Gram stain and Culture | - | - |
| Cytology | - | - |
| Fluid Protein (g/dL) | <3 | <3 |
| Fluid protein/serum protein ratio | <0.5 | <0.5 |
| Fluid Glucose (mg/dL) | Parallel with serum | Parallel with serum |
| Comments | Usually bilateral | Incidence of 5% with ascites |
Exudate
| Diagnosis | Parapneumonic effusions (uncomplicated) | Empyema | Pulmonary embolism | Tuberculosis | Malignancy | Rheumatoid | Chylothorax | Pancreatitis |
|---|---|---|---|---|---|---|---|---|
| Appearance | Turbid | Turbid to purulent | Straw-colored to bloody | Straw-colored to serosanguinous | Turbid to bloody | Turbid, green to yellow | Milky | Turbid |
| WBC (cells/mm3 or /µL) and Differential* | 5,000 - 25,000 PMN predominance | 25,000 -100,000 PMN predominance | 5,000 -15,000 PMN predominance | 1,000 - 5,000 Lymphocytic predominance | <10,000 Lymphocyte predominance | 1,000 - 5,000 Mononuclear predominance | 1,000 - 7,500 Lymphocyte predominance | 5,000 - 20,000 PMN predominance |
| RBC's (cells/mm3 or /µL) | <5,000 | <5,000 | 1,000 -100,000 | <5,000 | 1,000 - 100,000 | <1,000 | <1,000 | 1,000 -100,000 |
| Bacteriologic Gram stain and Culture | Positive | Positive | - | Positive AFB Smear or Culture | Negative | Negative | Negative | Negative |
| Cytology | Negative | Negative | Negative | Negative | Malignant cells | - | - | - |
| Fluid Protein | >3 g/dL (>30 g/L) | >3 g/dL (>30 g/L) | >3 g/dL (>30 g/L) | >3 g/dL (>30 g/L) | >3 | >3 | >3 | >3 |
| Fluid protein/serum protein ratio | High, >0.5 | High, >0.5 | High, >0.5 | High, >0.5 | High, >0.5 | High, >0.5 | High, >0.5 | High, >0.5 |
| Fluid LDH/serum LDH ratio | High, >0.6 | High, >0.6 | High, >0.6 | High, >0.6 | High, >0.6 | High, >0.6 | High, >0.6 | High, >0.6 |
| PH | <7.3 | <7.3 | >7.3 | <7.3 | <7.3 | <7.3 | - | >7.3 |
| Fluid Glucose (mg/dL) | Parallel with serum or decreased | 60 mg/dL | Parallel with serum | Parallel with serum or decreased | Parallel with serum or decreased | Very low (10-20 mg/dL) | Parallel with serum | Parallel with serum |
| Comments | Resolves with antibiotics only | Requires drainage plus antibiotics | Small to moderate effusion with alveolar infiltrate & volume loss | Positive PPD/TST | Cytology & pleural biopsy enable diagnosis in 80% | High rheumatoid titer (> 640) Cholesterol crystals | Triglycerides > 110 mg/dL, chylomicrons present, usually large | Elevated amylase (Pleural fluid:Serum >2) If glucose <30 mg/dL consider esophageal rupture |
Features of other disease conditions:
- Fungal infection: Positive KOH smear or culture
- Lupus pleuritis: Similar findings as with rheumatoid disease, except that glucose is usually not decreased, and presence of LE cells
- Urinothorax: Pleural/serum creatinine ratio >1.0 (average 9.15, range 1.09-19.8), low pH, sometimes low glucose
- Esophageal rupture: Elevated pleural fluid amylase and decreased pH (6.0)
- Hemothorax: Bloody appearance, increased RBC count, and elevated hematocrit
Additional information
- The most common causes of pleural effusion in adults are heart failure, malignancy, pneumonia, tuberculosis, and pulmonary embolism, whereas pneumonia is more common among children
- The diagnosis of why a given patient has a pleural effusion is typically based upon a combination of tests, taking into account the physical examination, medical history and risk factors
- Factors interfering with test results include:
- Failure to send specimen to lab immediately
- Amount of fixative and fluid is not adequate in the container for cytology
- Non-sterile collection technique or contamination of the sample
- Insufficient quantity of fluid for culture, especially AFB and fungal culture
- Traumatic tap resulting in bloody fluid
- Antimicrobial therapy before aspiration of fluid for culture
- Drugs (given below in high result section)
- Related laboratory tests include:
- Adenosine deaminase
- AFB culture/smear
- Albumin (serum)
- Amylase (serum)
- Antinuclear antibody (ANA)
- Bilirubin
- Blood culture
- C-reactive protein
- Carcinoembryonic antigen (CEA)
- Cholesterol
- Complete blood count (CBC)
- Glucose (Serum)
- Immunocytology
- Immunologic studies
- Lactate dehydrogenase (LDH)
- Lipid analysis
- Partial thromboplastin time (PTT)
- Pleural needle biopsy
- PPD
- Prothrombin time (PT)
- Rheumatoid factor
- Sedimentation rate
- Thoracoscopy
- Urinalysis
- Urine culture
This section covers Pleural fluid - Cells/Culture. The other section provides detailed information on other components of Pleural fluid analysis.
Consult your laboratory for their normal ranges as these may vary somewhat from the ones listed below.
Gross appearance
- Watery consistency, clear to pale yellow in color
Cells
- WBC's: <1,000 cells/mm3
- Polymorphonuclear cells: <25% of WBC's
- RBC's: <1,000 cells/mm3
- Cytology: No abnormal cells seen
Bacteriology
- Culture: Negative for bacteria, fungi, AFB
- Gram Stain: Negative for organisms
- AFB Stain: Negative for AFB
- Fungal Stains: Negative for fungi
This section covers Pleural fluid - Cells/Culture. The other section provides detailed information on other components of Pleural fluid analysis.
Increased RBC's (>100,000/mm3)
- Asbestos pleurisy
- Malignancy
- Post-cardiac injury syndrome
- Pulmonary embolism
- Trauma
Increased WBC's (>1,000/mm3)
- Acute asbestos pleurisy
- Chylothorax
- Fungal infections
- Leukemia
- Lymphoma
- Malignancy
- Mesothelioma
- Pancreatitis
- Parapneumonic effusions
- Postcardiac injury
- Pulmonary infarction
- Rheumatoid pleurisy
- Sarcoidosis
- Tuberculosis
- Viral infections
Increased polymorphonuclear cells (>50% of WBC's)
- Bacterial pneumonia
- Pancreatitis
- Parapneumonic effusions
- Pulmonary embolism
- Pulmonary infarction
Increased lymphocytes (>50% of WBC's)
- Coronary artery bypass surgery
- Lymphoma
- Malignancy
- Pulmonary embolism
- Rheumatoid pleurisy
- Sarcoidosis
- Tuberculosis
Increased eosinophils (>10% of WBC's)
- Benign asbestos effusions
- Certain infections
- Hydropneumothorax
- Parasitic infections
- Pneumothorax
Mesothelial cell predominance
- Chronic malignant effusions
- Empyema
- Following the use of sclerosing agents
- Mesothelioma
- Rheumatoid pleurisy
Infectious causes of pleural effusions may include:
- Bacterial
- Bacteroides
- E. coli
- Fusobacterium
- Klebsiella
- Legionella
- Nocardia
- Peptostreptoccus
- Pseudomonas
- S. pyogenes
- Staphylococcus aureus
- Streptococcus pneumoniae
- Fungal
- Aspergillus
- Coccidioides
- Histoplasma
- Mycobacterium tuberculosis
- Parasitic
- Entamoeba
- Paragonimus
Differential Diagnosis by type of pleural effusion:
- Transudates
- Atelectasis (early stage)
- Cirrhosis with ascites
- Congestive heart failure
- Hypoproteinemia as in nephrotic syndrome
- Myxedema
- Peritoneal dialysis
- Superior vena cava syndrome
- Urinothorax
- Exudates
- Abdominal causes
- Esophageal perforation
- Pancreatitis
- Postoperative
- Subphrenic abscess
- Chylothorax
- Immunologic causes
- Churg-Strauss syndrome
- Familial Mediterranean fever
- Lupus pleuritis
- Rheumatoid pleurisy
- Sarcoidosis
- Sjögren's syndrome
- Wegener's granulomatosis
- Infections
- Abdominal (upper abdominal, hepatic, or splenic abscess and hepatitis)
- Atypical (legionella, mycoplasma, q-fever)
- Bacterial (parapneumonic: simple or complicated, empyema)
- Fungal
- Parasite
- Tuberculosis
- Viral
- Neoplasms
- Leukemia
- Lung carcinoma
- Lymphoma
- Mesothelioma
- Metastatic carcinoma
- Other inflammatory causes
- Acute respiratory distress syndrome (ARDS)
- Benign asbestos pleural effusion
- Meig's syndrome
- Pulmonary embolism
- Trapped lung
- Uremia
- Radiation therapy
- Drugs
- Amiodarone
- Anticoagulants
- Bleomycin
- Bromocriptine
- Busulfan
- Dantrolene
- Granulocyte-macrophage colony stimulating factor (GM-CSF)
- Hydralazine
- Interleukin-2
- Methotrexate
- Methysergide
- Minoxidil
- Mitomycin-C
- Nitrofurantoin
- Para-aminosalicylic acid
- Practolol
- Procainamide
- Procarbazine
- Quinidine
- Tocolytic agents
This section covers Pleural fluid - Cells/Culture. The other section provides detailed information on other components of Pleural fluid analysis.
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