Serous

• Serous body cavities


  Those which surround or enclose various organs (heart, lungs, abdominal) and are lined with serous membranes
• Serous body cavities


  • Pericardial Cavity
  • Pleural Cavity
  • Peritoneal Cavity
• Visceral serous membrane


  Those directly lining the organ
• Parietal serous membrane


  The other membrane that will enclose the body cavities
• Serous fluid


  An ultrafiltrate of plasma
• Pressure forces maintaining serous fluid volume

  • Tissue colloidal osmotic pressure
  • Capillary hydrostatic pressure
  • Capillary colloidal osmotic pressure
  • Tissue hydrostatic pressure

  
• Effusion


  Accumulation of serous fluid always associated with a particular pathological process
• Types of effusions


  • Pericardial Effusion
  • Pleural Effusion
  • Peritoneal Effusion
• Pathologic causes of effusions

  • Increased capillary hydrostatic pressure
  • Decreased oncotic pressure
  • Increased capillary permeability
  • Lymphatic obstruction

  
• Oncotic pressure


  Brought about by proteins, pulls fluid from interstitial space or cavity towards blood vessel
• Hydrostatic pressure


  Causes filtration or sealing mechanism, fluid from blood vessel leaks into cavity
• Specimen collection


  1. Fluid aspiration from cavities

  2. EDTA tube for cell counts and differential

  3. Sterile heparinized tubes for microbiology and cytology

  4. Chemistry tests on clotted or heparinized tubes, pH maintained anaerobically in ice

  
• Macroscopic examination of serous fluids

  • Sanguineous
  • Purulent
  • Milky
  • Cholesterol crystals
  • Clotted

  
• Appearance of serous fluid

  Indicates pathological condition
• Chylous effusion


  Caused by thoracic duct leakage, milky/white appearance, predominantly lymphocytes, triglycerides >110 mg/dL, strongly positive Sudan III staining
• Pseudochylous effusion


  Caused by chronic inflammation, milky/green tinge, mixed cells, cholesterol crystals present, triglycerides <50 mg/dL, negative/weakly positive Sudan III staining
• Significance of pericardial fluid testing

  • Clear, pale yellow - normal
  • Blood-streaked - infection, malignancy
  • Grossly bloody - cardiac puncture, anticoagulants
  • Milky - chylous, pseudochylous

  
• Significance of peritoneal fluid testing

  • Clear, pale yellow - normal
  • Turbid - microbial infection
  • Green - gallbladder, pancreatic disorders
  • Blood-streaked - trauma, infection, malignancy
  • Milky - lymphatic trauma and blockage
  • Peritoneal lavage >100,000 RBCs/L - blunt trauma injury

  
• Routine chemistry tests for serous fluids

  Glucose, Lactate dehydrogenase (LD), Protein
• Additional chemistry tests for serous fluids

  • Alkaline phosphatase
  • Ammonia
  • Amylase
  • Bilirubin
  • Chloride
  • Lipids
  • pH
• Transudate


  Clear appearance, fluid:serum protein ratio <0.5, fluid:serum LD ratio <0.6, WBC count <1000/μL, no spontaneous clotting, pleural fluid cholesterol <45-60 mg/dL, pleural fluid:serum cholesterol ratio <0.3, pleural fluid:bilirubin ratio <0.6, serum-ascites albumin gradient >1.1
• Exudate


  Cloudy appearance, fluid:serum protein ratio >0.5, fluid:serum LD ratio >0.6, WBC count >1000/μL, possible spontaneous clotting, pleural fluid cholesterol >45-60 mg/dL, pleural fluid:serum cholesterol ratio >0.3, pleural fluid:bilirubin ratio >0.6, serum-ascites albumin gradient <1.1
• Light's criteria


  Fluid:serum protein ratio >0.5, fluid:serum LD ratio >0.6, serous fluid LDH >2/3 serum upper limit
• od circulation


  Fluid circulation
• Now if we compare the two values, more or less
• Light's Criteria


  Helps determine if the fluid collected is an EXUDATE
• Light's Criteria


  • First criteria: if fluid:serum ratio is more than 0.5
  • Second criteria: if fluid:serum LD ratio is more than 0.6
  • Third criteria: if serous fluid LDH level is more than two-thirds (2/3) of the serum upper limit normal level
• WBC count


  Presence of large amounts of WBC (more than 1000 cells per uL) is associated with an exudate
• Spontaneous clotting


  It is POSSIBLE with exudates
• Pleural fluid cholesterol


  More cholesterol
• Pleural fluid: serum cholesterol ratio

  Higher pleural fluid:serum cholesterol ratio seen in exudate
• Pleural fluid:bilirubin ratio


  Higher pleural fluid:bilirubin ratio in exudates
• Serum-ascites albumin gradient (SAAG)

  This is used to compute or report when the fluid in question is a peritoneal fluid. We don't use SAAG in a pericardial and pleural fluid only in peritoneal fluid.

  
• Higher values are seen in exudates except for SAAG which is higher transudate. And again very important to remember na kahit saan kayo pumunta, kahit mag medicine, you will still be asked about the Light's criteria. This is actually a high yield question for the boards.
• PLEURAL FLUID TESTING ALGORITHM

  1. Identify if the fluid is an Exudate or a Transudate

  2. Perform the supportive tests (addendum tests)

  
• Elevated amylase levels


  Seen in pancreatitis
• Increased adenosine deaminase (ADA) level coupled with abnormal WBC count or differential count with lymphocytosis


  May be associated with Tuberculosis
• High ADA levels + lymphocytosis on differential count for serous fluid

  Can maybe also rule in Tuberculosis
• TB is not only found in the lungs, it may actually spread on other parts of the body, such that when TB is disseminated it is called Disseminated TB or Miliary TB
• ADA of more than 40 ul + differential count with elevated granulocytes (>300 ul)


  If higher level of granulocytes are seen, it may indicate Bacterial Infection