Authors: Dr Vijay Shankar S, Dr Amita Kumari
1. What is pleural fluid?
It is the fluid present in the pleural cavity, located between the parietal and visceral pleural membranes..
2. What is the normal volume of pleural fluid?
3. What is the function of pleural fluid?
The pleural fluid is a thin serous fluid which acts as lubricating agent and prevents friction between the lungs and the ribs when breathing. It also keeps the lungs inflated.
4. How is pleural fluid collected?
The pleural fluid is collected by a procedure called thoracocentesis/pleural tap. This is a procedure where the needle is inserted into the chest wall, to collect/drain fluid collected in the pleural cavity
5. What are the differences between transudate and exudate?
The difference between transudate and exudate are as follows
| Transudate | Exudate | |
| Collection of fluid because of systemic disease where there is disturbance in regulation of fluid filteration and reabsorption | Fluid production due to direct involvement of peritoneal membranes | |
| Eg: Congestive heart failure, cirrhosis, nephritic syndrome | Eg: infections and malignancies | |
| Appeareance | Clear | Cloudy to turbid |
| Cellularity | Low | High |
| Proteins | Low | High |
| Clot | Does not clot | May clot |
| Specific gravity | Low | High |
| Albumin | Low | High |
| LDH levels | Less than 225U/L | Greater than 225U/L |
| Fluid to serum protein ratio | Less than 0.5 | Greater than 0.5 |
| Fluid to serum LDH | Less than 0.6 | Greater than 0.6 |
6. What is the significance of appearance/color of the pleural fluid?
| Appearance /color | Disease associated |
| Clear or pale yellow | Normal |
| White/turbid | Infections |
| Bloody | Tuberculosis, malignancy, trauma |
| Milky white | Chylous effusion due to leak from thoracic duct |
| Brown/anchovy sauce | Rupture of amebic abscess |
| Black | Fungal infections as in aspergillosis |
7. What is chylothorax?
Accumulation of milky/chylous fluid is called as chylothorax.
The characteristic features are: triglyceride level greater than110mg/dl. On microscopy lymphocytes and fat droplets are seen. Fat droplets can be seen by staining with sudan III.
The characteristic features are: triglyceride level greater than110mg/dl. On microscopy lymphocytes and fat droplets are seen. Fat droplets can be seen by staining with sudan III.
8. What are the differences between chylous and pseudochylous effusions?
The difference between the two are as follows
| Chylous | Pseudochylous | |
| Onset | Sudden | Gradual |
| Appearance | Milky white/yellow, bloody | Milky or greenish, metallic sheen |
| Microscopy | lymphocytosis | Mixed cellularity, cholesterol crystals present |
| Triglyceride level | Greater than 110mg/dl | Less than 50 mg/dl |
| Lipoprotein electrophoresis | Chylomicrons present | Chylomicrons absent |
9. What are the components of pleural fluid analysis?
The components are
Physical examination
Appearance
Color
Chemical examination
pH
Glucose
Protein
LDH
Adenosine deaminase
Amylase
Physical examination
Appearance
Color
Chemical examination
pH
Glucose
Protein
LDH
Adenosine deaminase
Amylase
Microbiologic examination
Gram stain
Acid fast Stain
Culture
Serologic examination( if required)
Antinuclear antibody (ANA)
Rheumatoid factor ( RF)
Tumor markers(in suspected malignancies)
Microscopic examination
For cell typing
To rule out malignancies
10. What is the significance of pH in pleural fluid analysis.?
Note that the pleural fluid pH should be interpreted with other diagnostic tests.
Pleural fluid pH below 7.2 indicates empyema which needs chest tube insertion and drainage (http://www.ncbi.nlm.nih.gov/pubmed/3307471 )
Pleural fluid below 6 – esophageal rupture
Pleural fluid greater than 7.4 – congestive cardiac failure
pH can help in differentiating tuberculous from malignant effusions. Recent Malignant effusions have higher pH.
Pleural fluid pH below 7.2 indicates empyema which needs chest tube insertion and drainage (http://www.ncbi.nlm.nih.gov/pubmed/3307471 )
Pleural fluid below 6 – esophageal rupture
Pleural fluid greater than 7.4 – congestive cardiac failure
pH can help in differentiating tuberculous from malignant effusions. Recent Malignant effusions have higher pH.
11. What is the significance of differential cell count in pleural fluid?
The different type of cells represents , different disease process. It gives clues to the probable diagnosis. The list is tabulated as below
| Type of cell | Diseases associated |
| Neutrophil | Bacterial pneumonia
Pulmonary infarction Pancreatitis Subphrenic abscess Early tuberculosis Transudate ( in around 10 %) |
| Lymphocytes | Tuberculosis
Viral infection Malignancies True chylothorax Rheumatoid pleuritis SLE Uremic effusion Transudate (approx 30%) |
| Eosinophils | Air in pleural space
Trauma Pulmonary infarction Congestive cardiac failure Parasitic or fungal infections Hypersensitivity reactions Drug reactions Rheumatologic desease Hodgkin disease
|
| RBC’s | Intrapleural malignancy ( 60% of cases)
Traumatic tap Pulmonary infarction Pleural infection Closed chest trauma Postmyocardial hepatic syndromes Hepatic cirrhosis |
| Immature blood cells | Chronic myeloid leukemia
Myeloid metaplasia( extramedullary hematopoiesis) |
12. What are the causes of foul smelling pleural fluid.?
The foul smelling pleural fluid is seen in
a. Anaerobic infections
b. Urinothorax (urinous/ammonical odour)
a. Anaerobic infections
b. Urinothorax (urinous/ammonical odour)
13. What are the causes of increased amylase in pleural fluid?
The causes of increased amylase in the pleural fluid are
a. Pancreatic disease
b. Esophageal rupture.
a. Pancreatic disease
b. Esophageal rupture.
14. What is the significance of macrophages in pleural fluid?
These cells have round to bean shaped nuclei and moderate amount of cytoplasm and phagocytosed dark cytoplasmic particles. These appear in groups or in sheet like appearance.
Giant multinucreated macrophages are seen in rheumatoid pleuritis. When they are in clumps, they can be mistaken for mesothelial cells or malignant cells.
Giant multinucreated macrophages are seen in rheumatoid pleuritis. When they are in clumps, they can be mistaken for mesothelial cells or malignant cells.
15. What special tests can be done in pleural fluid and in what conditions.?
The special tests are as follows
| Tests | Diseases |
| Adenosine deaminase
Gamma interferon PCR |
Tuberculosis |
| Rheumatoid factor | Rheumatic effusion |
| Antinuclear antibodies | SLE |
| Amylase | Esophageal rupture
Pancreatitis |
| CEA | Adenocarcinoma lung |
| Tryglycerides | Chylothorax |
| D –dimer test | Pulmonary embolism |
.
16. What is the role of cytological examination of pleural fluid?
Cytological examination is the common method for determining whether the exudate is benign or malignant.
The cells exfoliated into the pleural fluid can be studied by preparation of smears, liquid based cytology or cytospin preparations. Cell block study can also be done. The pitfall is that the absence of malignant cells DOES NOT rule out malignancy.
The cells exfoliated into the pleural fluid can be studied by preparation of smears, liquid based cytology or cytospin preparations. Cell block study can also be done. The pitfall is that the absence of malignant cells DOES NOT rule out malignancy.
17. What are the cytological features of malignancy in pleural fluid?
The cytological features of malignancy are
a. Cells can be in sheets, three dimensional clusters and in singles
b. Papillary or acinar structures
c. The nuclei show pleomorphism, coarse nuclei, irregular nuclear membranes, with prominent nucleoli
d. Multinucleation can be seen
e. Atypical mitosis and necrotic debris can be seen.
a. Cells can be in sheets, three dimensional clusters and in singles
b. Papillary or acinar structures
c. The nuclei show pleomorphism, coarse nuclei, irregular nuclear membranes, with prominent nucleoli
d. Multinucleation can be seen
e. Atypical mitosis and necrotic debris can be seen.
18. What is the significance of ADA levels in pleural effusions and what precautions should be taken for its interpretation.?
Adenosine deaminase (ADA) is useful in the diagnosis of tuberculous pleural effusion (TPE). ADA levels more than 95 IU/L indicates effusion of tubercular etiology.
Three important factors should be considered before interpreting ADA levels
http://journal.publications.chestnet.org/article.aspx?articleid=1045663
http://bmcinfectdis.biomedcentral.com/articles/10.1186/1471-2334-13-546
a. Age: ADA level decreases with age
b. Pleural protein: ADA levels increases with increase in protein levels
c. The incidence of tuberculosis in that particular region: the cut off values are different in countries with different levels of incidence of tuberculosis.
Three important factors should be considered before interpreting ADA levels
http://journal.publications.chestnet.org/article.aspx?articleid=1045663
http://bmcinfectdis.biomedcentral.com/articles/10.1186/1471-2334-13-546
a. Age: ADA level decreases with age
b. Pleural protein: ADA levels increases with increase in protein levels
c. The incidence of tuberculosis in that particular region: the cut off values are different in countries with different levels of incidence of tuberculosis.
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