General Principles for Various Body Fluids
Fluid should be collected in both EDTA tubes and tubes without anticoagulant. EDTA tubes are best for cell counts, cytologic examination, and total protein measurement, whereas tubes lacking anticoagulant are used for biochemical and microbiological analysis.
At least 1 mL of fluid should be collected in each tube if possible.7 It is recommended to consult with a reference laboratory for the most current guidelines regarding sample collection, storage, and transport for culturing abdominal, pericardial, thoracic, cerebrospinal, and synovial fluids. Direct preparations of highly cellular turbid fluid or concentrated preparations of low cellularity clear fluid should be made as soon as possible, especially when a delay in transportation cannot be avoided. Cytologic findings that may be seen with delayed processing of fluid samples include erythrophagocytosis, vacuolization of large mononuclear cells, and pyknosis. Bacterial overgrowth can also impair interpretation.8Body Fluid Analysis
Abdominocentesis, thoracocentesis, and pericardiocentesis techniques have been previously described in horses2,7,9,10 and cattle.2,11 Gross impressions such as the amount of fluid, color, and consistency/turbidity should be evaluated. Normal fluid should be light straw-colored and clear.11 Samples from thoracic, abdominal, and pericardial fluid should be evaluated on the basis of total nucleated cell counts (TNCC) and total protein concentration (TP). The TNCC and TP together aid the clinician in classification of the fluids into the broad categories of transudate, modified transudate, and exudate. However, microscopic analysis should always be performed to evaluate the cellular differential and to assess for neoplastic cells, organisms, or evidence of chronic hemorrhage. In adult horses, samples from the thoracic cavity are generally transudates if they have fewer than 5000 cells∕μL and a total protein of less than 2.5 g/dL, are modified transudates with 5000 to 15,000 cellsZμL and a total protein of 2.0 to 5.0 g/dL, and are exudates if the TNCC is greater than 10,000 to 15,000 cellsZμL and the TP is greater than 3.0 to 3.5 g/dL.12 Samples from the peritoneal cavity are similar except that modified transudates can have a TNCC of 1500 to 10,000 cells∕μL and a TP of 2.5 to 3.5 g/dL.8 TNCC and TP interpretations vary widely in cattle, and appropriate references should be consulted.11 Further information can be obtained in Chapters 30-32.
Synovial Fluid Analysis
Collection of synovial fluid should be aseptic, and a full description of techniques is found in other sources.13,14 Synovial fluid should be placed in an EDTA tube for cytologic analysis, as well as in a serum tube if a mucin clot test or cultures are desired.13 The gross and microscopic appearance of the synovial fluid, total nucleated cell count, protein concentration, viscosity, and mucin quality (assessed via the mucin clot test) are all important features to analyze when making interpretations of joint fluid.14 Normal joint fluid is clear to pale yellow, does not clot, and is highly viscous.
Although there is some variability in the TNCC obtained from normal joints from various locations, generally synovial fluid samples are of low cellularity (often < 1000 cells∕μL). Hemarthrosis should be distinguished from blood contamination, and the overall differential cell count should be interpreted in light of the degree of blood contamination. Overall, the percentage of neutrophils in normal
joint fluid should not be greater than 10% in the absence of significant blood contamination. Large mononuclear cells and small lymphocytes predominate in normal joint fluid. Neutrophilic inflammation can be due to septic inflammation, immune-mediated disease, or acute trauma. Bacterial cultures and sensitivities are recommended to rule out infectious organisms. Immune-mediated diseases affecting joints are relatively uncommon in the horse.13
Cerebrospinal Fluid Analysis
Please refer to Chapter 35.
REFERENCES
The complete list of references can be found at www.expertconsult.com.
Bronchoalveolar Lavage/Tracheal Washes
Please refer to Chapter 31.