Patterns of Disease: Body Fluids

Question 1

BODY CAVITY EFFUSIONS

Answer 1

Accumulations of fluid in mesothelial lined spaces:
Peritoneum (abdomen), pleura (thorax), pericardium.
Produced by mesothelial cells.
These fluids can be sampled on occasion- Abdominocentesis, thoracocentesis, pericardiocentesis.

Question 2

NORMAL FLUID

Answer 2

Normally a SMALL volume of peritoneal, pericardial and pleural fluid is present.
Very low protein concentration and cell counts.
Normally cannot be obtained from body cavities, unless there is a fluid. In large animals, a small quantity of fluid can be aspirated from the abdomen in normal conditions.

Question 3

FLUID FORMATION

Answer 3

Oncotic pressure- exerted by protein (albumin) in the blood; pulls water IN to vessels.
Hydrostatic pressure- blood pressure pushes fluid OUT of vessels in to interstitium/body cavities.
Usually these two forces are almost in equilibrium- hydrostatic pressure is slightly larger, allowing normal small amounts of body cavity fluid to form.

Question 4

BODY CAVITY EFFUSIONS

Answer 4

Divided in to three general categories, based on PROTEIN and CELL COUNT:
1. TRANSUDATE
2. MODIFIED TRANSUDATE
3. EXUDATE
This allows us to narrow down the mechanism of formation of the effusion.

Question 5

TRANSUDATE FORMATION

Answer 5

• DECREASED ONCOTIC PRESSURE eg. hypoalbuminaemia- less protein in the blood means less water is pulled in, so it remains in the body cavity.
• INCREASED HYDROSTATIC PRESSURE- mainly due to cardiac issues (myocardial insufficiency, portal hypertension). More fluid is pushed out of vessels in to interstitium/body cavities.

Normal oncotic pressure, increased hydrostatic pressure = effusion.

Question 6

TRANSUDATE

Answer 6

Grossly ranges from colourless to straw coloured.
NUCLEATED CELL COUNT- <25g/L
Expected cells include macrophages, mesothelial cells, and rarely nondegenerate neutrophils.
In the HORSE, may see up to 75-80% nondegenerate neutrophils- this is the exception; will still be considered transudate.

Question 7

EXUDATE FORMATION

Answer 7

INFLAMMATION increases vascular permeability via inflammatory mediator cells.
This allows protein (albumin) to be lost from vessels.
Nucleated cell count and protein count are increased:
NUCLEATED CELL COUNT- >3 cells x10^9/L.
PROTEIN COUNT- >35g/L
Exudate formation may be seen with a variety of inflammatory causes- pancreatitis, bacterial infections, bowel perforation, irritants (bile, urine).

Question 8

IS IT SEPTIC?

Answer 8

SEPTIC- microorganisms, especially intracellular, are present.
Neutrophils may be nondegenerate or degenerate, depending on type of infectious agent present.
Just because bacteria cannot be seen does not mean they aren’t there! Cytology is not very sensitive for bacteria.
If in doubt, culture.
Degenerate neutrophils are often indicative of bacterial infection- if these cells are seen, look for bacteria.

Question 9

MODIFIED TRANSUDATE

Answer 9

A ‘catch-all’ category for fluids not fitting easily in to either transudate or exudate.
Either the nucleated cell count or total protein count is increased, but is not above the exudate range.
NUCLEATED CELL COUNT- 3-5 cells x10^9/L.
TOTAL PROTEIN COUNT- >25g/L.
Formation: Progression of transudate. Chronic accumulation of transudative fluid causes increased pressure that irritates mesothelial cells. The cells respond by proliferating and sloughing in to the effusion, increasing nucleated cell count.
When they die, they attract macrophages (inflammatory mediators)- though not enough to class the fluid as an exudate.
If mild inflammation occurs and persists, an exudate may eventually form.

Question 10

MESOTHELIAL CELLS

Answer 10

Repair and line body cavities.
Contact between normal cells prevents mitosis.
Sloughed (irritated) cells have none of this inhibition (they have become individualised), so replicate and becomr REACTIVE.
-> large, abnormal nucleus, visible nucleoli.
Reactive cells are NOT neoplastic! Neoplasm can occur (mesothelioma), and it is hard to differentiate between the two.

Question 11

SPECIAL BODY CAVITY EFFUSIONS

Answer 11

• Chylous effusions
• Non-septic exudate of FIP (wet form)
• Gastrointestinal rupture
• Neoplastic effusions
• Haemorrhagic effusions
• Urinary tract rupture
• Bile peritonitis

Question 12

CHYLOUS EFFUSION

Answer 12

Formed by leakage of chyle from the lymphatic system in to a body cavity (usually the thorax)
Chylomicrons give the fluid a milky appearance- strawberry milkshake if red blood cells are present! (haemorrhage)
In the anorexic animal, chylomicrons will not be present, so will not give a milky appearance to the effusion.
Causes include:
-IDIOPATHIC- ~70% feline chylothorax cases
-THORACIC NEOPLASIA
-CARDIAC DISEASE
-DIAPHRAGMATIC HERNIA
-THORACIC DUCT RUPTURE (rare)

Question 13

CHYLOUS EFFUSION- DIAGNOSIS

Answer 13

• Small mature lymphocytes should predominate
• Neutrophils may also accumulate due to the irritating properties of the effusion.
• Chylous effusions have HIGH TRIGLYCERIDE concentrations compared to serum
• Triglycerides are measured to diagnose when lymphocytes don’t proliferate
• Neutrophils can be seen pinocytosing chylomicrons- vacuolated cytoplasm.
• Cholesterol concentration should be EQUAL TO or LOWER than serum concentration
• Repeated drainage may result in a peripheral lymphopaenia and incite a localised inflammatory reaction.

Question 14

FELINE INFECTIOUS PERITONITIS (WET FORM)

Answer 14

Exudate is odourless, straw to gold coloured.
HIGH PROTEIN >35g/L, variable, often LOW, CELL COUNT.
Slides have a thick, stippled, proteinaceous background due to increased protein.
Granular protein precipitate visible on low mag.
Predominant cell type- DEGENERATE NEUTROPHILS (60-80%).
Lesser numbers of macrophages and lymphocytes.

Question 15

GASTROINTESTINAL RUPTURE or ENTEROCENTESIS

Answer 15

Acute GI rupture and inadvertent enterocentesis (‘gut tap’- use ultrasound to avoid) have a similar cytologic appearance: NUMEROUS MIXED BACTERIA, PROTOZOA, INGESTA etc.

• Presence of a significant number of NEUTROPHILS is far more suggestive of RUPTURE, but is not diagnostic.
• Automated cell count will be inaccurate due to (food) particles in fluid.
• If in doubt, aspirate again and correlate with clinical signs.

Question 16

NEOPLASTIC EFFUSION

Answer 16

Neoplasms commonly cause effusions, but tumour cells may or may not exfoliate.
Look at criteria of malignancy of cells to determine whether they are neoplastic or not.

Question 17

HAEMORRHAGIC EFFUSIONS

Answer 17

Is it a true haemorrhagic effusion, or has a vessel been hit while sampling?
ERYTHROPHAGOCYTOSIS- true haemorrhage. Acute. Erythrocytes and reactive mesothelial cells.
HAEMATOIDIN- true haemorrhage, occurring for more than 72 hours. Low P02.
HAEMOSIDERIN- true haemorrhage, occurring for more than 72 hours. Normal P02.

Question 18

URINARY TRACT RUPTURE

Answer 18

Urine acts as an irritant, so neutrophil levels will increase over time.
Protein levels are usually low (urine dilutes them), but may vary- can produce transudate, modified transudate, or exudate.
CREATININE should be higher in effusion than in serum- >2x serum is DIAGNOSTIC.
Urea will more rapidly equilibrate between the peritoneum and the vascular space, and may not be different from serum, so is not useful.
Urine crystals may be present.

Question 19

BILE PERITONITIS

Answer 19

Bile enters peritoneum eg. due to gallbladder rupture.
Normally forms an exudate.
Green/yellow substance visible in macrophages and free in background.
Effusion levels of bilirubin will be higher than serum levels.

Question 20

CEREBROSPINAL FLUID (CSF)

Answer 20

Sampling and testing is useful in patients with neurological disease, neck/limb pain, fever of unknown origin.
Different pathologies may show similar CSF changes cytologically- CSF sampling rarely gives a diagnosis, but can eliminate many possibilities.
Absence of changes does NOT eliminate the possibility of a process affecting the CNS.

Question 21

CSF- SAMPLE PROCESSING

Answer 21

Requires prompt analysis- total protein and nucleated cell count (should be LOW normally).
Sample in to a plain serum tube.
Postal sample- if volume allows, send two aliquots- one unaltered for protein, one with 10% autologous serum for better cell preservation.
Can also reserve some sample for say, bacterial culture, as well as sending some to the lab.

Question 22

CSF- TOTAL PROTEIN

Answer 22

Measured by SULFOSALICYLIC ACID method. Proteins are denatured by acids and form a precipitate. The turbidity of the sample is then compared against a standard solution.
Normal- Clear, colourless.
Spectrum is seen from normal to abnormal- progressively becomes more white and cloudy.

Question 23

CSF- CELL COUNT

Answer 23

Use haemocytometer, as numbers are often too low for an automated analyser.
Consider NUMBER and TYPE of cells eg. red cells, white cells.

Question 24

CSF- CYTOLOGY

Answer 24

Cytospin and Romanowsky stain for cytology.
Allows microscopic examination of CSF for cells etc.
May see eg. meningeal cells, neutrophils (ABNORMAL), mononuclear cells/macrophages (ABNORMAL), infectious agents eg. yeasts (cryptococcus)

Question 25

SYNOVIAL FLUID

Answer 25

Fluid present in joints between bones. Lubricates joints, allowing easy movement of bones over one another. 
Reasons for sampling:
-Joint swelling
-Limping
-Monoarthropathy
-Polyarthropathy
-Fever of unknown origin
-Generalised pain 
-Weakness
Let the pathologist know if one or multiple joints are affected! The more information given, the more you can get back.

Question 26

SYNOVIAL FLUID- GROSS EVALUATION

Answer 26

Normally transparent to colourless- note any turbidity.
Presence of blood- iatrogenic (from sampling- fluid often normal then becomes bloody) or haemorrhagic (fluid is uniformly bloody)?
Viscosity- normal synovial fluid produces long strands (2.5cm) when slowly expressed from a needle of touched with an applicator.

Question 27

SYNOVIAL FLUID- SAMPLE PROCESSING

Answer 27

Small volume (one drop)- make a SMEAR- allows cytological evaluation and estimated nucleated cell count (NCC).

Larger volume- allows NCC, total protein and cytology.
<1000/ul cats.
Collect in plain or EDTA tubes.
EDTA preserves cells but also dilutes sample.

Question 28

SYNOVIAL FLUID- CYTOLOGY

Answer 28

Examine background.
Assess number of red cells.
Differential count- large mononuclear cells (macrophage, synoviocyte), lymphocytes, neutrophils (normally less than 5% in dogs), eosinophils (should be absent)
Detecting organisms in synovial fluid can be difficult due to it’s antibacterial activity- a sample can be septic without bacteria etc. being seen.

Question 29

WINDROWING

Answer 29

Cells are seen on direct smears of synovial fluid (eg. red cells due to contamination on sampling), they tend to line up in rows. This is normal based on the viscosity of synovial fluid, and is called windrowing.