Pleural Fluid Analysis

Sample for Pleural Fluid Analysis

1. The sample is aspirated from the pleural cavity.

Procedure for thoracentesis:

1. This is better to do ultrasonography-guided aspiration.
   1. The patient will be in a sitting position.
   2. Give local analgesia.
   3. Do the percussion and mark the upper level of fluid.
   4. Ideally, it is done on the posterior side, roughly 10 cm away from the spine.
   5. Enter the syringe below 1 to 2 intercostal spaces from the upper border.

Indications for Pleural fluid aspiration (Thoracentesis)

1. This may be diagnostic.
2. Or maybe therapeutic to relieve the pain and dyspnoea.
3. Gram and AFB stain may be done.
4. It is used for culture.
5. It can be used for the PCR for the diagnosis of tuberculosis.

Contraindications for Pleural fluid aspiration

1. Avoid in case of thrombocytopenia.
2. In case the volume is too small.
3. If the patient has a bleeding tendency.
4. If there is a skin disease in the area of the puncture.
5. If the patient is on anticoagulant therapy.

Definition of pleural fluid:

1. 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.
2. Pleural fluid may be:
   1. Exudate is mostly due to infections or neoplastic processes.
      1. Other conditions like collagen diseases, trauma, pulmonary infarction, and drug hypersensitivity may cause exudate.
   2. Transudate is due to congestive heart failure, nephrotic syndrome, hypoproteinemia, and cirrhosis.

Gross appearance of Pleural Fluid:

1. In the case of empyema, it has a foul odor and a thick and pus-like appearance.
2. 1. Chylothorax fluid is opalescent and pearly fluid.
      1. The chylous fluid contains a high concentration of triglycerides and a positive Sudan III stain.
      2. Pseudochylous fluid contains a high concentration of cholesterol and cholesterol crystals.

Difference between chylous and pseudochylous pleural fluids:

2. How to differentiate hemothorax and hemorrhagic exudate:
   1. Advise hematocrit (Hct) on the pleural fluid:
      1. In the case of hemothorax = Hct is similar to the blood.
      2. In chronic membranous disease, fluid = Hct will be much lower.

Microscopic examination of pleural fluid:

1. Total cells count:  
   1. The cell count >1000 /mL suggests exudate.
   2. Polys indicate an acute inflammatory condition like pneumonia, early tuberculous effusion, and pulmonary infarction.
   3. If >50% of white cells are lymphocytes, it indicates tuberculosis or neoplasm.
   4. The presence of RBCs indicates neoplasm, intrathoracic bleeding, or malignancy.

Significance of the various cell types in the pleural fluids:

Biochemical findings of pleural fluid:

1. Protein: 
   1.  >3 g/dL indicates exudates.
   2. <3 g/dL indicates transudates.
   3. Albumin gradient is a better factor than total protein.
      1. Albumin gradient = Pleural albumin – serum albumin.
      2. A value 1.1 g/dL or more indicates transudate.
      3. Value <1.1 g/dL indicates exudate.
   4. Total protein ratio = Fluid total protein – serum total protein
      1. If the ratio is >0.5  indicates exudate.
2. pH:
   1. Normal pH =  7.4
   2. <6.0 indicates an esophageal rupture and allows the influx of acid or gastric fluid from the stomach.
   3. >7.4 indicates malignancies.
   4. Pleural fluid pH <7.3 may indicate the need for chest tube drainage and antibiotics in case of pneumonia.
3. Glucose:
   1. The glucose level is like a serum glucose level.
   2. Glucose <60 mg/dL may be seen in:
      1. Tuberculosis.
      2. Malignancy.
      3. Rheumatoid arthritis.
      4. Empyema.
4. Amylase:
   1. This may be elevated in malignant tumors.
   2. It will be raised in case of pancreatitis, and this amylase may be the first to be raised in the pleural fluid.
   3. Rupture of the esophagus with leakage of salivary amylase.
5. Lactate dehydrogenase (LDH):
   1. Pleural fluid LDH / serum LDH if >0.6 is seen in the exudate.
6. Triglycerides:
   1. This is done to diagnose chylous pleural effusion.
   2. In the chylous fluid, triglycerides are >110 mg/dL.

Significance of the chemicals in the pleural fluids:

7. Carcinoembryonic antigen (CEA):
   1. CEA is raised in case of pleural effusion due to GIT malignancy.
   2. This may be raised in the case of breast carcinoma.
8. Exudate:
   1. Pleural fluid cholesterol >60 mg/dL.
   2. Pleural fluid cholesterol: serum cholesterol = >0.3
   3. Pleural fluid bilirubin: serum bilirubin = 0.6 or more.
9. Transudate:
   1. Proteins are <3 g/dL.

Microscopic examination of pleural fluid: 

1. Cytology:
   1. This will be positive in 50 to 60% of the malignant pleural effusion.
   2. The most common site is the lungs and breast.
   3. The third common cause is lymphoma.
2. The case of pleural fluid may see the staphylococcus aureus, Enterobacteriaceae, anaerobes, and mycobacterium tuberculosis.
   1. Advice:
      1. Gram stain.
      2. Culture.
      3. AFB stain.
3. Gram stain and culture:
   1. Advise gram stain before starting the antibiotics.
   2. Advise culture for tuberculosis, and this may take 4 to 6 weeks.
   3. Advice for fungal culture because this may cause pleural effusion.
4. Immunologic tests: It differentiates pleural effusion from the immunologic and non-inflammatory processes.
   1. The most common tests advised are an anti-nuclear antibody (ANA) and Rheumatoid factor.

 Normal Pleural fluid:

Source 2

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