Page 141 - Canine Lameness

9.3 ­Groos, BrocheBocas, cand CyraroBo EceBacyBra 113

9.3 Gross, Biochemical, and Cytologic Examination

Joint fluid analysis and evaluation typically involve assessment of gross appearance, protein con-
centration, total nucleated cell count (TNCC), and cytologic interpretation. Other biochemical
parameters, such as glucose and lactate, can also be measured but the availability of these tests
may vary from laboratory to laboratory. A summary of typical findings in non‐affected canine
joints and general interpretation guidelines are provided in Figure 9.2 and Table 9.1.

9.3.1 Gross Appearance
Gross appearance of synovial fluid assesses turbidity, color (particularly regarding the presence of
blood), viscosity, and the amount of volume sampled from each joint. In healthy patients, joint
fluid is typically clear and pale yellow, as well as thick and viscous. While these characteristics will
be determined by the laboratory, it is also helpful to note such qualities at the time of sample col-
lection. Viscosity can be evaluated empirically by forming a string of synovial fluid between the
tips of the fingers, but this is only recommended to be performed in cases with ample amount of
sample. A fingertip stretch distance of ~2–3 cm is generally considered appropriate viscosity.
Recording the presence or absence of blood is particularly helpful to the clinical pathologist for
distinguishing blood contamination due to sample collection from overt hemorrhage.

9.3.2 Protein Concentration
While protein concentrations are typically estimated using a refractometer, automated chemistry
measurements and electrophoresis have also been used to determine and/or characterize such.
However, some laboratories will not perform automated protein concentration analyses on joint
fluids if the fluid is too viscous. When using a refractometer, it is important to note that the pres-
ence of other solutes in the fluid may affect the measurement of protein concentration, as does
underfilling EDTA tubes or aspirating joints previously treated with intra‐articular injections.
Therefore, it is critical to use appropriately sized EDTA tubes due to the possibility of erroneous
results secondary to EDTA dilution when tubes are underfilled. Alternatively, if sufficient sample
is available, red top tubes can be used to measure protein concentrations.
Normal protein levels in synovial fluid are between 1.5 and 3.0 g/dl (MacWilliams and Friedrichs
2003). In disease states or when there is inadvertent sampling of blood, protein concentrations can
begin to rise and approach levels similar to serum or plasma.

9.3.3 Total Nucleated Cell Counts
TNCCs are typically performed by an automated analyzer, most often on samples collected into
EDTA. TNCCs within synovial fluid are predominately composed of white blood cells. However,
other nucleated cells may also be included in the analyzer count as part of the TNCC (e.g. synovio-
cytes, nucleated red blood cells, neoplastic cells, etc.) making cytological analysis in addition to the
TNCC imperative. If an analyzer is not available, or the amount of synovial fluid retrieved is insuf-
ficient to process through an analyzer, hemocytometers or direct smears can be used to assess cel-
lularity. If a direct smear is used to estimate cellularity, the average number of cells per 40×
objective high‐power field over 10 fields can be multiplied by 1000 to yield an approximate number
of cells per microliter. However, the evaluator should be aware that visual estimates are less
accurate than automated methods. The viscosity of joint fluid can make estimation of cellularity