Classification of pleural and ascitic effusions
Pleural and ascitic fluid should routinely be tapped to determine the type of effusion and it’s classification. Once this has been performed, then the diagnostic pathway can be decided. Whilst this table classifies effusion by a number of categories, simply determining its character (colour and transparency) and the SG is often sufficient to classify it - this can therefore usually be performed in-house. The effusions can also be submitted to an RCVS Specialist in Cytology for examination (some in universal pot and some in EDTA, plus air dried smears, made within 30 to 60 minutes, from the buffy coat of a spun sample) and to a laboratory for culture and sensitivity (swab in transport medium).
Effusion Type |
Transparency |
Colour |
Specific Gravity |
Protein Content (g/l) |
Cell Count
per ml |
Predominant Cell Type |
True Transudate |
Translucent
clear |
Yellow or colourless |
< 1.018 |
< 25 |
<1500
(-) |
- |
Modified Transudate |
Partially opaque
turbid |
yellow to pink |
>1.018 |
>30 |
1500 to 5000
(+) |
Variable Cell Type
Note: red cells are not uncommon (PCV <5%) |
Exudate
|
opaque
turbid |
yellow to brown |
>1.035 |
>30 |
>5000
(+++) |
Neutrophil |
Chyle
|
opaque
turbid |
white or pink |
>1.030 |
>25 |
1500 to 10000
(++) |
Lymphocyte
TGs are very high compared to serum |
|
Ascites (which is a modified transudate), can often be due to right sided heart failure.
If due to heart failure then there should also be: jugular distension on clinical and an enlarged caudal vena cava on a lateral chest radiograph +/- pleural effusion. Ultrasound should also show a congested liver and enlarged hepatic veins, as well as echocardiographic evidence of right heart disease. In cats pleural effusion caused by heart failure can be a modified transudate or a chylous effusion.
Recommended reading Martin & Corcoran (2006) Notes on: Cardiorespiratory disease of the dog and cat, 2nd ed. Blackwell Science. ISBN 0-632-03298-7. |
