CPD ACCREDITED ARTICLE
From Cloudy to Clear
Effusions Made Easy
Emma Hooijberg DiplECVCP
Department of Companion Animal Clinical Studies
Faculty of Veterinary Science University of Pretoria
[email protected]
Introduction
An effusion is the fluid that can accumulate in a body
cavity due to various different pathologies. Mechanistically,
effusions are caused by transudation, exudation, rupture of a
blood/lymph vessel/ hollow organ, or neoplasia. It is usual to perform a 100-cell differential count,
or at least estimated the proportions of the different
nucleated cell populations, when examining the
smears. Note should be made of any infectious
agents, foreign material, background or atypical cells.
Types of effusions include transudates and exudates, but
also haemorrhagic effusions, chyle and uroperitoneum. The
composition of the fluid gives clues as to the pathology that
caused it, and the goal of fluid cytology is to describe this
composition, by looking at cellularity, cell types present,
protein concentration, SG and the presence of other
substances like bilirubin or creatinine. Normal pleural fluid has a protein concentration of <
25 g/L with very low numbers of macrophages and
mesothelial cells. Mesothelial cells line the pleural,
pericardial and peritoneal cavities and will be present
in most effusions. They are large cells, present singly
or in clusters, as seen in Figure 1.
Sample Preparation Mesothelial cells become hyperplastic very quickly in
response to an increased volume of any type of fluid.
Numbers increase, and they display many atypical
features – multinucleation, mitotic figures, prominent
Effusions can be examined in-house or sent away to
reference laboratory for evaluation. Fluid should be collected
into an EDTA tube for cytological analysis, and into a plain
tube for culture. Two direct smears (using the blood-smear
technique) should be made from the EDTA-fluid. If the
samples are to be sent away, these smears should be left
unstained, packaged in plastic slide-keepers and stored at
room temperature until sent. The EDTA and serum tubes
should be stored at 4°C.
For in-house analysis, the total nucleated cell count (TNCC)
can be determined from the uncentrifuged EDTA fluid sample
on an automated cell counter – in most cases the same
analyzer used for measuring haematology/ CBC samples. If
this is not available, an estimate of cellularity (“low” or “high”)
can be made from the direct smears, with some experience.
After TNCC measurement, the EDTA tube is centrifuged.
Total protein and SG of the supernatant is measured with a
refractometer. If the TNCC is < 30 000 cells/ µL, or cellularity
is low on the direct smear, smears should be made from
the sediment after centrifugation. The supernatant should be
saved in case any biochemical tests need to be performed.
If the fluid is very bloody, prepare a buffy coat smear to
concentrate any nucleated cells of interest.
Figure 1: An aggregate of morphologically normal mesothelial
cells (500x; Diff-Quick)
Issue 01 | MARCH 2018 | 21