Fluid Analysis:- part 6 – Pleural Fluid Analysis, Aspiration procedure (Thoracentesis),
Pleural Fluid Analysis
Sample for Pleural Fluid Analysis
- The sample is aspirated from the pleural cavity.
Procedure for thoracentesis:
- This is better to do ultrasonography-guided aspiration.
- The patient will be in a sitting position.
- Give local analgesia.
- Do the percussion and mark the upper level of fluid.
- Ideally, it is done on the posterior side, roughly 10 cm away from the spine.
- Enter the syringe below 1 to 2 intercostal spaces from the upper border.
Indications for Pleural fluid aspiration (Thoracentesis)
- This may be diagnostic.
- Or maybe therapeutic to relieve the pain and dyspnoea.
- Gram and AFB stain may be done.
- It is used for culture.
- It can be used for the PCR for the diagnosis of tuberculosis.
Contraindications for Pleural fluid aspiration
- Avoid in case of thrombocytopenia.
- In case the volume is too small.
- If the patient has a bleeding tendency.
- If there is a skin disease in the area of the puncture.
- If the patient is on anticoagulant therapy.
Definition of pleural fluid:
- The pleural fluid is obtained from the pleural cavity, which is between the parietal pleural membrane lining the chest wall and the visceral pleural membrane covering the lungs.
- Pleural fluid may be:
- Exudate is mostly due to infections or neoplastic processes.
- Other conditions like collagen diseases, trauma, pulmonary infarction, and drug hypersensitivity may cause exudate.
- Transudate is due to congestive heart failure, nephrotic syndrome, hypoproteinemia, and cirrhosis.
- Exudate is mostly due to infections or neoplastic processes.
Gross appearance of Pleural Fluid:
- In the case of empyema, it has a foul odor and a thick and pus-like appearance.
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- Chylothorax fluid is opalescent and pearly fluid.
- The chylous fluid contains a high concentration of triglycerides and a positive Sudan III stain.
- Pseudochylous fluid contains a high concentration of cholesterol and cholesterol crystals.
- Chylothorax fluid is opalescent and pearly fluid.
Difference between chylous and pseudochylous pleural fluids:
Characters featured | Pseudochylous fluid | Chylous fluid |
Appearance | Milky and green tinge | Milky and white |
White blood cells | Mixed cell types | Predominantly lymphocytes |
Triglycerides | <50 mg/dL | >110 mg/dL |
Cholesterol | Present | absent |
Sudan III stain | Negativ/weekly positive | Strongly positive |
Etiology | Chronic inflammation | Thoracic duct leakage |
- How to differentiate hemothorax and hemorrhagic exudate:
- Advise hematocrit (Hct) on the pleural fluid:
- In the case of hemothorax = Hct is similar to the blood.
- In chronic membranous disease, fluid = Hct will be much lower.
- Advise hematocrit (Hct) on the pleural fluid:
Appearance | Clinical significance |
Clear, pale yellow | Normal |
Bloody | Hemothorax (traumatic injury) and hemorrhagic effusion (malignancy) |
Turbid, white | Microbial infection (due to the presence of WBCs), e.g., tuberculosis, bacteria, immunologic diseases |
Milky | Leakage from the thoracic duct, pseudochylous material from the chronic inflammation |
Microscopic examination of pleural fluid:
- Total cells count:
- The cell count >1000 /mL suggests exudate.
- Polys indicate an acute inflammatory condition like pneumonia, early tuberculous effusion, and pulmonary infarction.
- If >50% of white cells are lymphocytes, it indicates tuberculosis or neoplasm.
- The presence of RBCs indicates neoplasm, intrathoracic bleeding, or malignancy.
Significance of the various cell types in the pleural fluids:
Type of the cells | Significance of the various type of cells |
Neutral (polys) | seen in pneumonia, pancreatitis, and pulmonary infarction |
Lymphocytes | Tuberculosis, viral infection, malignancy, and immunologic diseases (SLE) |
Eosinophils | >10% of cells seen in the allergic reaction, parasitic infestation, and trauma due to the presence of air or blood in the pleural cavity |
Plasma cells | Seen in tuberculosis |
Mesothelial cells | There are normal and reactive forms without any significance |
Malignant cells | Seen in primary lung adenocarcinoma, small cell carcinoma, and metastatic carcinoma |
Biochemical findings of pleural fluid:
- Protein:
- >3 g/dL indicates exudates.
- <3 g/dL indicates transudates.
- Albumin gradient is a better factor than total protein.
- Albumin gradient = Pleural albumin – serum albumin.
- A value 1.1 g/dL or more indicates transudate.
- Value <1.1 g/dL indicates exudate.
- Total protein ratio = Fluid total protein – serum total protein
- If the ratio is >0.5 indicates exudate.
- pH:
- Normal pH = 7.4
- <6.0 indicates an esophageal rupture and allows the influx of acid or gastric fluid from the stomach.
- >7.4 indicates malignancies.
- Pleural fluid pH <7.3 may indicate the need for chest tube drainage and antibiotics in case of pneumonia.
- Glucose:
- The glucose level is like a serum glucose level.
- Glucose <60 mg/dL may be seen in:
- Tuberculosis.
- Malignancy.
- Rheumatoid arthritis.
- Empyema.
- Amylase:
- This may be elevated in malignant tumors.
- It will be raised in case of pancreatitis, and this amylase may be the first to be raised in the pleural fluid.
- Rupture of the esophagus with leakage of salivary amylase.
- Lactate dehydrogenase (LDH):
- Pleural fluid LDH / serum LDH if >0.6 is seen in the exudate.
- Triglycerides:
- This is done to diagnose chylous pleural effusion.
- In the chylous fluid, triglycerides are >110 mg/dL.
Significance of the chemicals in the pleural fluids:
Chemical parameter | Significance in various diseases |
Glucose | Decreased in rheumatoid arthritis, purulent infection |
Triglycerides | Increased in chylous effusion |
Amylase | Increased in pancreatitis, esophageal rupture, and malignancy |
Lactate | Increased in bacterial infection |
LDH | Increased in exudate |
pH | Decreased in pneumonia |
- Carcinoembryonic antigen (CEA):
- CEA is raised in case of pleural effusion due to GIT malignancy.
- This may be raised in the case of breast carcinoma.
- Exudate:
- Pleural fluid cholesterol >60 mg/dL.
- Pleural fluid cholesterol: serum cholesterol = >0.3
- Pleural fluid bilirubin: serum bilirubin = 0.6 or more.
- Transudate:
- Proteins are <3 g/dL.
Microscopic examination of pleural fluid:
- Cytology:
- This will be positive in 50 to 60% of the malignant pleural effusion.
- The most common site is the lungs and breast.
- The third common cause is lymphoma.
- The case of pleural fluid may see the staphylococcus aureus, Enterobacteriaceae, anaerobes, and mycobacterium tuberculosis.
- Advice:
- Gram stain.
- Culture.
- AFB stain.
- Advice:
- Gram stain and culture:
- Advise gram stain before starting the antibiotics.
- Advise culture for tuberculosis, and this may take 4 to 6 weeks.
- Advice for fungal culture because this may cause pleural effusion.
- Immunologic tests: It differentiates pleural effusion from the immunologic and non-inflammatory processes.
- The most common tests advised are an anti-nuclear antibody (ANA) and Rheumatoid factor.
Normal Pleural fluid:
Source 2
Characteristics | Values |
Gross appearance | Clear, light yellow |
Volume | 10 mL |
pH | 7.4 (or greater) |
RBCs | Nil |
WBCs | <300 /mL |
Protein | <3.0 g/dL |
Glucose | 70 to 100 mg/dL |
Alkaline phosphatase |
Adult male = 90 to 240 units/L Adult female <45 years = 76 to 196 units/L Adult female >45 years = 87 to 250 units/L |
Amylase | 138 to 404 units/L |
Lactate dehydrogenase (LDH) | It is like the serum level |
Bacteria | Negative |
Fungus | Negative |
Cytology | Negative for malignant cells |
carcinoembryonic antigen (CEA) | <5 ng/mL |
Questions and answers:
Question 1: What is the significance of CEA in pleural fluid?
Question 2: What is the normal pH of the pleural fluid?