Flashcards in Patterns of Disease: Body Fluids Deck (29):
BODY CAVITY EFFUSIONS
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.
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.
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.
BODY CAVITY EFFUSIONS
Divided in to three general categories, based on PROTEIN and CELL COUNT:
2. MODIFIED TRANSUDATE
This allows us to narrow down the mechanism of formation of the effusion.
-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.
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.
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).
IS IT SEPTIC?
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.
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.
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.
SPECIAL BODY CAVITY EFFUSIONS
-Non-septic exudate of FIP (wet form)
-Urinary tract rupture
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.
-IDIOPATHIC- ~70% feline chylothorax cases
-THORACIC DUCT RUPTURE (rare)
CHYLOUS EFFUSION- DIAGNOSIS
-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.
FELINE INFECTIOUS PERITONITIS (WET FORM)
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.
GASTROINTESTINAL RUPTURE or ENTEROCENTESIS
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.
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.
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.
URINARY TRACT RUPTURE
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.
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.
CEREBROSPINAL FLUID (CSF)
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.
CSF- SAMPLE PROCESSING
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.
CSF- TOTAL PROTEIN
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.
CSF- CELL COUNT
Use haemocytometer, as numbers are often too low for an automated analyser.
Consider NUMBER and TYPE of cells eg. red cells, white cells.
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)
Fluid present in joints between bones. Lubricates joints, allowing easy movement of bones over one another.
Reasons for sampling:
-Fever of unknown origin
Let the pathologist know if one or multiple joints are affected! The more information given, the more you can get back.
SYNOVIAL FLUID- GROSS EVALUATION
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.
SYNOVIAL FLUID- SAMPLE PROCESSING
Small volume (one drop)- make a SMEAR- allows cytological evaluation and estimated nucleated cell count (NCC).
Larger volume- allows NCC, total protein and cytology.
Collect in plain or EDTA tubes.
EDTA preserves cells but also dilutes sample.
SYNOVIAL FLUID- CYTOLOGY
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.