Lecture on Synovial and Serous Fluids
Synovial Fluid
Definition: Synovial fluid, also known as joint fluid, plays a crucial role in bathing and lubricating the joints, such as those in the knees, elbows, fingers, and toes.
Function: It helps joints glide smoothly across each other where friction can develop.
Structure: The joint space is lined with a synovial membrane, which consists of two types of synovial cells:
Phagocytic synovial sites: These cells are responsible for producing collagenase, an enzyme that degrades collagen.
Hyaluroninate: A mucopolysaccharide that imparts unique viscosity to the synovial fluid.
Formation: Synovial fluid is formed through ultrafiltration of plasma across the synovial membrane, followed by secretions from synovial cells, effectively resulting in plasma with additives.
Composition of Synovial Fluid
Similarities to Plasma: The fluid's glucose and uric acid levels are comparable to plasma; however, total protein and immunoglobulin concentrations may vary due to filtration.
Viscosity: The unique viscosity is crucial for the maintenance of articular cartilage.
Key Terms Related to Synovial Fluid
Arthritis: Defined as any inflammation of a joint.
Arthrocentesis: A procedure for collecting synovial fluid from a joint.
Volume Characteristics: The volume of synovial fluid is generally low compared to serous fluids.
Types of Joint Disorders Diagnosed by Synovial Fluid Analysis
Non-inflammatory Disorders
Inflammatory Disorders: e.g., rheumatoid arthritis and lupus.
Septic Disorders: Resulting from bacterial, fungal, or mycobacterial infections.
Hemorrhagic Disorders: Associated with conditions such as sickle cell anemia, hemophilia, or trauma.
Overlap: Recognize how septic and inflammatory conditions can co-occur.
Collection and Processing of Synovial Fluid
Practice of Arthrocentesis: Conducted by physicians using sterile needles and syringes, typically collecting 3 to 10 mL, though often less may be obtained.
Portion Collection: The collected fluid can be divided into three tubes:
Tube 1: No anticoagulant for chemical or immunological studies.
Tube 2: Anticoagulant, generally purple top, for microscopic studies.
Tube 3: Sterile anticoagulant for microbiology tests.
Timeliness of Processing: It's crucial to process the collected fluid quickly to avoid alterations in cell counts and chemical composition due to continuing cellular metabolism.
Physical Examination of Synovial Fluid
Normal Appearance: Clear or pale yellow fluid.
Abnormal Colors:
Red or brown: Potentially indicates trauma or disruption of the synovial membrane.
Green or cloudy: May suggest infection or high cellular material.
Viscosity Assessment: Normal synovial fluid is viscous, with strings measuring 3-6 cm when dripped.
Decreased viscosity may occur during inflammation due to neutrophils breaking down hyaluronidase.
Clotting Properties: Normal fluid does not clot; clotting may indicate blood contamination or a pathological process involving fibrin or fibrinogen.
Cell Count and Differential Analysis
Methods: Red blood cell (RBC) and white blood cell (WBC) counts can be performed using a hemocytometer or analyzers; treatment with hyaluronidase ensures proper mixing for analysis.
Expected Cell Counts:
RBCs: Less than 2,000 cells/µL
Increased counts could be due to traumatic tap or hemorrhagic effusion.
WBCs: Typically less than 200 cells/µL; elevations may indicate infection.
Differential Count: Various WBC types can be identified, including macrophages, lymphocytes, and neutrophils.
Hemocytometer Counting: Involves counting all nine squares for accurate results.
Crystal Screening in Synovial Fluid
Crystal Identification: Important tests for diagnosing gout and pseudogout.
Technique: Wet prep under a polarized microscope to identify crystals based on their birefringent properties.
Gout Crystals: Monosodium urate, long, needle-like formations; appear yellow when aligned with the polarizer (negative birefringence).
Pseudogout Crystals: Calcium pyrophosphate dihydrate, shorter and blunt; appear blue when aligned with the polarizer (positive birefringence).
Cholesterol Crystals: Present as flat rectangular shapes with notched corners.
Chemical Analysis of Synovial Fluid
Glucose Levels: Typically equivalent to plasma glucose; decreased levels indicate inflammation or sepsis.
Total Protein Levels: Approximately one-third that of plasma protein; increased levels suggest various joint diseases, frequently linked to inflammatory processes.
Uric Acid Levels: Elevated levels may indicate the presence of monosodium urate crystals.
Lactate Levels: Elevated levels may reflect increased anaerobic glycolysis; clinical usefulness remains uncertain.
Microbiology Testing for Synovial Fluid
Gram Stains and Cultures: Used to identify infectious agents, commonly derived from blood infections; typical pathogens include:
Neisseria gonorrhoeae
Staphylococcus aureus
Streptococcus pneumoniae
Haemophilus influenzae
Various gram-negative organisms (e.g., E. coli).
Overview of Serous Fluids
Definition: Serous fluids are produced by serous membranes lining the lungs, heart, and abdominal organs.
Function: While they protect and separate organs, these fluid-filled spaces can become sites of fluid accumulation due to disease processes.
Types of Serous Fluids:
Pleural Fluid: Around the lungs.
Pericardial Fluid: Around the heart.
Peritoneal Fluid: In the abdominal cavity.
Formation: Like synovial fluid, serous fluids result from ultrafiltration of plasma, regulated by:
Capillary permeability
Hydrostatic pressure
Oncotic pressure from plasma proteins (albumin)
Absorption by lymphatics.
Terms Related to Serous Fluids
Ascites: Excess peritoneal fluid often seen in liver disease.
Chyle: Milky fluid from intestinal lymphatics, indicative of chylomicrons or triglycerides.
Effusion: Abnormal fluid accumulation in body cavities due to pathological processes.
Mesothelial Cells: Line serous membranes and can be seen during examination of serous fluid.
Collection and Testing of Serous Fluids
Collection Procedures:
General term for fluid removal is paracentesis.
Specific terms: thoracentesis (pleural fluid), pericardiocentesis (pericardial fluid), peritoneocentesis (peritoneal fluid).
Testing Purpose: Fluid analysis can be for microbiological, chemical, cell count, and cytology studies.
Type Categorization:
Transudates: Resulting from systemic diseases (e.g., congestive heart failure).
Exudates: Indicating localized disease processes (e.g., infections, tumors).
Differentiation of Transudates and Exudates
Physical Characteristics:
Transudates: Clear or pale yellow, similar viscosity to serum, do not clot due to lack of fibrinogen.
Exudates: Cloudy, variable colors, can form clots due to fibrinogen presence.
Cell Counts: Expect more cells in exudates, reflecting the presence of infection or inflammation.
Cellular Analysis of Serous Fluids
Cell Types Identified:
Neutrophils (indicative of bacterial infections)
Lymphocytes (often in TB or neoplastic diseases)
Mesothelial cells (normal lining cells)
Malignant cells (large, blue-staining)
LE cells: Found in lupus patients, characterized by engulfed nuclear material.
Cytological Examination of Serous Fluids
Cytology Studies: Using Cytospin for slide preparation, sent unstained for flexible laboratory processing.
Crystal Identification and Gram Stains: As part of cytology.
Chemical Tests on Serous Fluids: Include total protein, LDH, glucose, amylase, triglycerides, pH, and CEA (tumor marker).
Laboratory Analysis and Documentation
Serous Fluid Documentation: Ensuring quick transport and accurate labeling for laboratory analysis.
Testing Considerations: Always differentiate between transudates and exudates while examining physical properties and chemical composition for accurate diagnosis.