The classification of body cavity effusions into transudates (T), modified transuates (MT) or exudates (EX) is an important step in diagnosing the primary disease. The total nucleated cell count (TNCC) and cytological findings are the most important parameters in differentiating MT from EX as total proteins in both categories may overlap, while transudates have both a low cell count and low total proteins.

A delay of 24-48 hours between collection and analysis is a common occurrence in practice when samples are posted to an external diagnostic laboratory.

The aim of this study was to determine if there was any difference between the automated TNCC and cytological findings of fluids analysed within one hour (fresh), 24h and 48 hours post collection.

Materials and Methods

Samples from 17 effusions (11 canine and 6 feline) were collected into EDTA. Automated TNCC counts (Cell-Dyn 3700 analyser) and cytological assessment of direct smears and cytospin preparations were performed on fresh samples and after storage at room temperature (210C) for 24 and 48 hours.

Results

TNCC (x109/L)

See Figure 1.

Only 1 exudate sample was reclassified as a modified transudate after 48 hours, this had an initial TNCC of 7.5 x109/L which dropped to 5.1 x109/L.

The preservation of the cells commonly deteriorated with time, especially the morphology of neutrophils. Intracellular organisms were found in the fresh samples from 4 cases but were not found in the stored samples from 3 of these cases.

There was 1 neoplastic effusion (suspected carcinoma); malignant neoplastic cells were still present in the samples stored for 24 and 48 hours.

Conclusions

There was a trend of a decrease in automated TNCC of both MT and EX with storage, however this was only statistically significant in MT after 48h of storage. In only 1 case was this decrease enough to change the classification of the fluid. There is deterioration in the morphology of neutrophils with time. Intracellular bacteria may be missed on aged samples.

Although the current sample size is small, collection is ongoing. The trends observed may be come significant with a higher sample number.

Figure 1. Repeated sample ANOVA * Fresh vs 48 hrs p< 0.047.