Effusion & fluid analysis

What are the features of the body cavity fluid?

• Little fluid (<5 ml) is present in these cavities in small animals

• Ultrafiltrate of blood

• Low cellularity and protein concentration

• Lined by mesothelial cells

What does the rate of fluid formation depend on?

• Starling’s forces = gradients of hydrostatic and oncotic pressures between the vessels and the body cavities

• The degree of mesothelial and endothelial permeability

• The integrity of lymphatic drainage

How do you carry out body cavity fluid analysis?

• Gross —> colour & turbidity

• Total nucleated cell count (TNCC) —> EDTA tube → haematology analyser

  • WBC, RBC and haematocrit

• Total protein concentration

  • Refractometer

• Cytological examination

  • Direct/ sediment smear

What other tests would you want to carry out other than just cytology?

• Biochem - cholesterol, creatinine ect.

• Microbiology - culture and PCR

What are the different classifications of body cavity effusions?

What cells are being shown in the normal body cavity fluid cytology?

1. Mesothelial cells

2. Macrophages

3. Lymphocytes

4. Neutrophils

(very few cells in the normal body cavity)

What are the features of Protein-poor (pure) transudate?

• Clear & colourless

• TNCC <1.0 x10^9/L

• TP < 25 g/L

• Macrophages & lymphocytes typically predominate; fewer neutrophils; rare mesothelial cells

  

^^ cytospin prep

What causes protein-poor transudate?

Inc hydrostatic pressure

• Cardiac failure

• Portal hypertension

• Overhydration (excessive fluids)

• Venous thrombus

Dec osmotic pressure

• Severe hypoalbuminaemia (protein losing nephropathy, protein losing enteropathy, hepatic insuf)

Organ rupture

• Uroabdomen, bilious effusion (will become exudate)

What are the features of Protein-rich (modified) transudate?

• Clear & colourless to amber or pink

• TNCC 1.0-5.0 x10^9/L

• TP >25 g/L

• Macrophages, lymphocytes, neutrophils; variable numbers of mesothelial cells (dep on irritation —> binucleated, on L of image)

^^^ cytospin prep

What causes Protein-rich transudate?

Increased systemic or local hydrostatic pressure

• Congestive heart failure

• Portal hypertension

• Venous thrombus

• Neoplasia

• Organ torsion or volvulus

Other

• FIP (see later)

• Chronic protein-poor transudate

Further investigation of transudate

What are the features of an exudate?

• Turbid, amber, yellow or brown

• TNCC >5.0 x10^9/L

• TP >25-30 g/L

• Mostly neutrophils, fewer lymphocytes & macrophages; variable numbers of mesothelial cells

^^^ direct smear

What causes an exudate?

Septic

• Bacteria —> haematogenous / lympho spread, FB, penetrating wounds, from other tracts

• Fungi —> systemic mycosis

• Protozoa —> toxoplasmosis, neosporosis, leishmaniosis

• Parasites —> cestodes

Non-septic

• Organ inflam (e.g. pancreatitis, steatitis, inflammatory/necrotic neoplasm)

• Irritants (e.g. urine, bile)

• FIP

• Eosinophilic (very rare)

What is being shown here?

Degenerate neutrophils when encounter bacteria

Fungal hyphae on R

What further investigations are needed if exudate is suspected?

What are the features of FIP fluid?

• Yellow & hazy / cloudy

• Usually < 5.0 x109/L, but can be higher

• High, often >45 g/L (very high yet poorly cellular)

• Usually neutrophils predominate; variable numbers of macrophages; few lymphocytes, but can rarely predominate

How do you diagnose FIP?

• Rivalta test

  • distilled water + vinegar → precipitation line if +ve

  • lower specificity

• Fluid albumin : globulin

  • >0.8 = FIP excluded; <0.4 = FIP likely

• Serum a1-acid glycoprotein >1,5g/L

• Direct IFA for FCoV within effusion macros / RT PCR for FCoV in fluid

  • Supportive of FIP

  (don't have a test that is diagnostic —> indicated infected with FCoV but may not develop into FIP)

What are the features of the fluid of a haemorrhagic effusion?

• Serosanguinous to red

• RBC / HCT similar or slightly less than peripheral blood

• TP similar / slightly less than peripheral blood

• Blood (± platelets); macrophages + erythrophagia and/or HGB breakdown products (circled) ; variable numbers of mesothelial cells

What can cause haemorrhagic effusion?

• Trauma

• Neoplasm —> imaging/ neoplastic cells on cytology

• Organ torsion

• Coagulopathy —> coagulation profile

• Idiopathic / Iatrogenic

How can haemorrhagic effusion be investigated?

• CBC / coagulation profile

• Imaging studies

• Search for neoplastic cells on cytology

How do you differentiate between true and iatrogenic haemorrhage?

PLT = platelets

Erythrophagic = destruction of RBCs by macros

How would you describe a chylous effusion?

• Milky

• TNCC and TP variable

  • TP high

• Lymphocytes predominate; with time, the numbers of neutrophils and macrophages increase; occasional mesothelial cells, but numbers increase with time

What further tests can you do for a chylous effusion?

• Fluid TRIG > Serum TRIG (usually much higher)

• Distinguished from pseudochylous effusion

What are the causes of chylothorax?

• CV dx

• Mediastinal mass (e.g. lymphoma, thymoma, granuloma)

• Diaphragmatic hernia

• Lung torsion

• Chronic coughing

• V+

• Iatrogenic / idiopathic

What are the features of the fluid in bile effusions?

• Brown, orange, yellow or green

• TNCC & TP —> Starts as transudate & quickly becomes exudate

• Neutrophils predominate; variable numbers of macrophages & mesothelial cells; yellow to green to blue-black granular material (bile) or amorphous, smooth, blue material (mucus)

How do you confirm the presence of bile inside the body cavity?

Fluid bilirubin > serum bilirubin

Caused by rupture of gallbladder or common bile duct

What are the features of the fluid in uroabdomen?

• Yellow, clear to turbid

• TNCC & TP starts as transudate & quickly becomes exudate

• Neutrophils predominate; variable numbers of macrophages & mesothelial cells; urinary crystals may be seen

How do you confirm uroabdomen?

Fluid creatinine > serum creatinine

Caused by rupture of urinary tract (usually bladder)

How do neoplasms cause effusions?

• Compression of blood vessels & lymphatics

• Inflam

• Haemorrhage

• Necrosis

• Cell exfoliation

• Inc vasc permeability

  (can be associated with diff types of effusion)

What is being shown here?

Neoplasia in cytology

Top right = reactive mesothelial cells, not neoplasia

What are the features of synovial fluid?

• Lubricates joint surfaces

• Provides O2 & nutrients to chondrocytes in articular cartilage

• Removal of chondrocyte waste

What is synovial fluid usually like?

<0.5 mL with gel-like consistency

What is the normal synovial fluid count in dogs vs cats?

Dogs = <3000/uL

Cats = <1000/uL

How do you analyse synovial fluid in cytology?

What is normal?

• Put in EDTA tube & plain tube (for culture)

• Prepare direct fresh smears

  • Proteinaceous background

  • Should be less than 2 cells per HPF

  • Predominance of mononuclear cells (small lymphocytes, macrophages and synoviocytes)

What are the different types of joint disease?

• Suppurative joint cells —> neutrophils more than 10% = neutrophilic inflam

  • Infectious or immune, neoplasia, drug induced

• Non-suppurative —> increased (typically mildly) numbers of mononuclear cells (lymphocytes, macrophages, synoviocytes)

What can cause non-suppurative joint disease?

• Secondarily to orthopaedic disease (e.g. cranial cruciate ligament rupture, hip dysplasia, elbow dysplasia, patella dislocation)

• Trauma

• Genetic

• Obesity

• Diet

What is being shown in each of these images?

Left - suppurative joint disease = high cellularity (neutros)

Right - non-suppurative joint disease = macros & small lymphos