Comprehensive Guide to Pleural and Pericardial Fluid Analysis: Diagnostic Insights and Clinical Procedures
Fluid Analysis, Pleural and pericardial fluids serves two main purposes. First, it helps distinguish whether these fluids are transudative or exudative. Transudative fluids are typically a result of imbalances in pressure within the body, while exudative fluids are more often caused by underlying diseases or inflammatory processes. Second, this analysis is crucial in identifying potential causative organisms, particularly in cases of infection. In essence, it’s a valuable diagnostic tool that helps determine the nature of the fluid accumulation and provides insights into the presence of infections or other underlying medical conditions.
The testing process closely parallels that of cerebrospinal fluid (CSF), with specific gravity being a key consideration, while chloride assessment is typically omitted. The most dependable method for distinguishing between transudate and exudate involves the simultaneous analysis of pleural fluid and serum for total protein and lactic dehydrogenase (LD) levels. A transudate is characterized by a serous fluid total protein to serum protein ratio below 0.5, along with an LD ratio below 0.6. If the fluid is identified as a transudate, further testing is unnecessary. If a substance is identified as an exudate, further investigations like Gram staining, cultures, and counterimmuno-electrophoresis are necessary. When there’s a suspicion of malignancy, it’s advisable to undergo cytologic examination and biopsy for a more comprehensive evaluation.
Specimen Collection (Pericardial & Pleural Fluid)
1. Patient Preparation:
- Explain the procedure to the patient, and obtain informed consent.
- Position the patient sitting upright or in a semi-reclined position, with the head and upper body supported.
2. Gather Necessary Supplies:
- Sterile gloves and drapes
- Antiseptic solution (e.g., iodine-based or chlorhexidine solution)
- Sterile drape or towels
- Syringes and needles
- Sterile collection containers
3. Sterile Technique:
- Ensure aseptic technique throughout the procedure to minimize the risk of infection.
- Wear sterile gloves, and use a sterile field for the procedure.
4. Identify the Puncture Site:
- Locate the site for needle insertion, which is typically in the posterior axillary line, between the ribs. This site is determined based on clinical assessment and imaging studies.
5. Anesthetize the Skin:
- Inject a local anesthetic at the chosen puncture site to numb the skin and underlying tissues.
6. Insert the Needle:
- After the skin is adequately anesthetized, a healthcare provider inserts a needle (usually an 18- or 21-gauge needle) through the skin and into the pleural space.
- The needle should be inserted at a slight angle, aiming for the lower part of the rib above the chosen site to avoid injury to intercostal vessels and nerves.
- As the needle penetrates the pleural space, pleural fluid will start to flow into the syringe.
7. Collect Pleural Fluid:
- As pleural fluid enters the syringe, withdraw the plunger slowly to collect the desired amount of fluid.
- The amount of fluid collected depends on the clinical purpose, such as diagnosis, therapeutic drainage, or relief of symptoms.
8. Monitor the Patient:
- Throughout the procedure, monitor the patient’s vital signs and symptoms for any signs of distress.
9. Remove the Needle:
- Once the required amount of pleural fluid has been collected, carefully remove the needle from the pleural space.
10. Post-Procedure Care:
- Apply a sterile dressing to the puncture site to minimize the risk of infection.
- Monitor the patient for any complications, such as pneumothorax (collapsed lung) or bleeding.
It is advisable to obtain a separate specimen in EDTA for cell count.
Routine Examination (Fluid Analysis) Pericardial & Pleural Fluid
Evaluate the quantity, color, and transparency of the fluid. Normal fluid should appear straw-colored and clear without coagulation or a pellicle.
Utilize a refractometer or copper sulfate solutions to determine specific gravity. The specific gravity of pleural fluid can vary, but it is typically around 1.012 to 1.022. This range reflects the relative concentration of solutes and particles in the pleural fluid compared to water. Specific gravity is an important parameter used in the analysis of pleural fluid to assess whether the fluid is transudative or exudative. Transudative pleural effusions often have a lower specific gravity, indicating that they are more like a filtrate of plasma, while exudative effusions tend to have a higher specific gravity, suggesting a higher concentration of proteins and other solutes due to an underlying disease or inflammatory process.
Pleural and pericardial fluids usually have very few cells, typically ranging from 0 to 8 cells per mm3. The predominant types of cells found in these fluids are lymphocytes and mesothelial cells.
Differences between Transudate and Exudate
|Appearance||Clear||Cloudy or turbid|
|Colour||Watery or straw||Turbid to purulent or bloody|
|Cell count||<1×109/L Lymphocytes and mesothelial cells||>1×109/L Neutrophils early but mononuclear cells later|
|Glucose||Same as serum||Same as serum or reduced (>50% of serum level)|
|Total proteins||<20 g/L (<50% serum level)||≥20 g/L|
|Rivalta Test||Negative or faint||Positive|
|LD||<60% of serum activity||>60% of serum activity.|
|Fluid total protein to serum total protein ratio||<0.5||>0.5|
|Fluid LD to serum LD ratio||<0.6||>0.6|
Estimation of Proteins:
The method aligns with CSF testing; however, due to the higher protein content in these fluids, they must be diluted before protein estimation. The degree of dilution depends on the specific gravity, with results adjusted accordingly.
Estimation of Globulins:
Typically, a qualitative test is performed, such as the Rivalta test on serous fluids. The required reagent is prepared by adding a drop of glacial acetic acid to distilled water. Normal fluids should not produce any cloud in the reagent, while a transudate may generate a faint cloud, and an exudate will result in a distinct cloud.
Estimation of Glucose:
It’s crucial to measure glucose levels in pleural fluid as it can provide valuable diagnostic information. When the glucose level in pleural fluid falls below 3.5 mmol/L (equivalent to 60 mg/100 ml), or if it’s 2.3 mmol/L (40 mg/100 ml) lower than the simultaneous plasma glucose level, it is considered to be at a decreased level. This decrease in glucose concentration can be observed in various conditions, including bacterial infections, especially when the exudate is purulent (containing pus), rheumatoid arthritis, malignant pleuritis (cancer-related inflammation of the pleura), and tuberculous pleuritis (pleural inflammation due to tuberculosis).
The pH of normal pleural fluid typically measures around 7.64. When the pH drops below 7.30, it may be indicative of various serious conditions like empyema, malignant disorders, collagen disorders, tuberculosis, esophageal rupture, or haemothorax. If the pleural fluid pH falls within the range of 7.3 to 7.4, it usually suggests a less concerning, benign condition. A pH lower than 6.0 is highly suggestive of an esophageal rupture.
In the case of pericardial fluid, a pH below 7.1 is often associated with connective tissue diseases and bacterial infections. A pH reading between 7.2 and 7.4 is typically linked to neoplasms (abnormal tissue growth), idiopathic disorders of unknown cause, tuberculosis, or uraemic pericarditis caused by kidney dysfunction. A pH higher than 7.4 is commonly seen in post-cardiotomy states and individuals with hypothyroidism.
When an exudate is suspected and an infective process is a concern, it is essential to perform cultures. The third container, previously set aside, is used for this purpose, and Gram and acid-fast staining are fundamental components of fluid examination.
In cases of fungal diseases, an appropriate culture is often required.
These are employed for the identification of specific bacterial antigens, such as S. pneumoniae, and can be performed on the fluid.
The determination of tumor markers in pleural fluid can aid in the diagnosis of certain malignancies. These tests are conducted when the presence of malignant cells is suspected, and they can be positive in cases of adenocarcinoma of the lung, breast, and ovary. In addition to the tests mentioned above, supplementary tests may be deemed necessary in specific clinical scenarios.
The viscosity of the fluid can be assessed by aspirating it in a pipette and observing the length of the falling drop. A normal viscosity is indicated when the falling drop draws into a band of 5 cm or longer.
Mucin (Hyaluronic Acid) Testing:
To evaluate mucin content, 5 ml of a 1:5 diluted fluid is mixed with 0.14 ml of 7N acetic acid. The resulting precipitate is examined immediately and after 2 hours. A tight, ropy mass is considered good, while softer, shreddy precipitates are categorized as fair, and poor precipitates indicate shreds of mucin in a turbid solution, suggesting reduced hyaluronic acid content.
Wet Preparation for Crystals and Inclusions:
A drop of fluid is placed on a clean slide and lightly covered with a cover slip. This preparation is then examined under a microscope, with specific features indicating various conditions. For example, needle-like crystals of urates may be seen in gouty arthritis, while small, multiple, dark inclusions in polymorphs could suggest rheumatoid arthritis, typically involving immunoglobulins with RA factor activity.
In conclusion, the testing of pleural and pericardial fluids is a critical diagnostic process that involves a series of evaluations and examinations to determine their nature and potential underlying conditions. Additional tests may be necessary based on the clinical context.
Work up of pleural effusion
|Pleural fluid protein to serum protein ratio||<0.5||No further tests required|
|Pleural fluid LD1 to serum LD ratio||<0.6|
|Pleural fluid protein to serum protein ratio||>0.5||Gram stain, culture, total WBC and differential counts, cytology, pH, glucose, α-amylase, tumour markers pleural biopsy|
|Pleural fluid LD to serum LD ratio||>0.6|