Serum-Effusion Albumin Gradient in Dogs with Transudative Abdominal Effusion

Evaluation of a new multiple regression model based on biochemical parameters for the distinction of canine exudates and transudates

BACKGROUND

The classification of effusions in human medicine currently uses biochemical parameters of verified analytical accuracy, while veterinary medicine is traditionally guided by protein content (TP) and total nucleated cell count (TNCC) in the effusion, without solid scientific support.

OBJECTIVE

We aimed to assess the accuracy of the current veterinary classification system to distinguish transudates from exudates and create new tools involving biochemical parameters that better classify canine cavitary effusions.

METHODS

Clinical, laboratory, and imaging data from 250 canine pleural and peritoneal effusions were retrospectively and prospectively collected, organized, and statistically evaluated. Multiple logistic regression analysis was performed using biochemical and cellular parameters.

RESULTS

For identifying exudates, the accuracy (87.7%, n = 204) of the best traditional classification system (TNCC > 3000 cells/μL) was similar to that of the individual biochemical cutoff values with the greatest accuracy in the abdominal cavity (eg, cholesterol, CHO-E > 40.1 mg/dL, 87.3%, n = 55). The accuracy of albumin (ALB-E > 0.8 g/dL) in the pleural cavity was nonetheless higher (100%, n = 23). The best multiple predictive models for any cavity used the percentage of neutrophils and CHO-E (n = 72), presenting an accuracy, sensitivity, and specificity for the diagnosis of exudate of 88%, 96%, and 67%, respectively.

CONCLUSIONS

Biochemical classification of pleural effusions has a higher accuracy than the traditional system (based on TP and TNCC). Utility and cutoff of analytes are different for each cavity. Implementing a multiple regression model or establishing ratios or gradients with concurrent serum values adds no significant improvement in the diagnostic potential of distinguishing transudate and exudates in dogs.

The predominance and diagnostic value of neutrophils in differentiating transudates and exudates in dogs

BACKGROUND

There is disagreement in the literature about the proportion of neutrophils expected in canine transudates. A cutoff of <30% neutrophils has been recommended for distinguishing transudates from exudates, but its validity has not been established.

OBJECTIVE

The aim of this study was to evaluate differential cell counts in canine effusions and analyze the percentage and number of neutrophils in transudates and exudates.

METHODS

Effusion data were obtained retrospectively from 263 dogs with pleural or peritoneal effusion. Low-protein transudates, high-protein transudates, and exudates were classified using the total protein (TP) concentration and total nucleated cell count (TNCC). Differential percentages and absolute neutrophil counts were compared by the effusion type and underlying etiology.

RESULTS

Low-protein transudates (n = 63), high-protein transudates (n = 84), and exudates (n = 77) had a median (range) of 35% (0%-100%), 59% (0%-100%), and 90% (50%-98%) neutrophils (P < .0001). All effusions with <50% neutrophils were transudates, but 53% of transudates had ≥50% neutrophils, and 69% had ≥30%. Median neutrophil counts were 62/µL (0-892/µL), 538/µL (0-4550/µL), and 45 590/µL (5400-496 800/µL) in low-protein transudates, high-protein transudates, and exudates, respectively (P < .0001). Neutrophil counts correlated with TNCC (r²  = 0.99), such that using neutrophil cutoffs did not affect effusion classifications in most cases. Neutrophil percentages and counts were higher in effusions from dogs with uroabdomen and sepsis (P < .01); neutrophil counts were lower in dogs with hepatic insufficiency (P < .0001). Uroabdomen usually caused low-protein, high-neutrophil exudates.

CONCLUSIONS

Although effusions with <50% neutrophils are transudates, most transudates and exudates have ≥50% neutrophils, limiting the diagnostic usefulness of % neutrophils for classifying effusions. Absolute neutrophil cutoffs did not notably improve effusion classification but could warrant future studies.