Traditional veterinary classification divides PEs in transudates (resulting from decreased colloid-osmotic pressure [COP]), modified transudates (resulting from increased hydrostatic pressure [HP]) and exudates (resulting from increased vascular permeability) based on effusion total protein (TPp) and total nucleated cell count (TNCCp). In humans, PEs are divided in transudates or exudates based on Light's criteria (LDHp, PE/serum LDH ratio, and TPp/TPs ratio). If a transudate is found, TPs determine whether it results from an increased HP or a decreased COP. Subsequently, LDHp resulted to be the test of Light's criteria with the best performance. The aim of this study was to compare, in dogs with PEs, the diagnostic accuracy of LDHp-TPs in distinguishing exudates (i.e., LDHp >2/3 of the upper serum reference interval) from transudates (TPs ≥4.0 g/dL for HP-transudates; TPs <4.0 g/dL for COP-transudates) in comparison to the traditional veterinary classification method (adopting textbook TPp-TNCCp cut-off values).

PEs were classified, based on pathophysiology of formation, in decreased COP-transudates, increased HP-transudates, and exudates. The disease causing the PE was used as gold standard for establishing the underlying pathophysiology. For both classification methods sensitivity, specificity, and accuracy were calculated and frequency of agreement between these methods and the true nature of the PE was compared (McNemar Chi–square test with Yates' correction).

One-hundred PEs were studied: 7 COP-transudates, 18 HP-transudates, and 75 exudates. The LDHp-TPs method correctly classified 73/75 exudates (2 misclassified as HP-transudate; sensitivity = 97%; specificity = 93%; accuracy = 98%), 7/7 COP-transudates (100% sensitivity, specificity, and accuracy), and 18/18 HP-transudates (sensitivity = 100%; specificity = 98%; accuracy = 98%). The traditional veterinary classification misclassified 30/75 exudates: 14 as HP-transudates, two as COP-transudates, and 14 were unclassifiable (i.e., discordant information deriving from TPp and TNCCp), (sensitivity = 60%; specificity and accuracy undeterminable due to the presence of unclassifiable PEs). Of the 18 HP-transudates, TPp and TNCCp misclassified 12 effusions: seven as CO-transudates and five were unclassifiable (sensitivity = 33%; specificity and accuracy undeterminable [see above]). All the 7 COP-transudates were correctly classified using the traditional veterinary classification (sensitivity = 100%; specificity and accuracy undeterminable [see above]). The overall accuracy (i.e., the number of correctly classified PE) was 98% (95% CI, 95–100%) for the LDHp-TPs method and 58% (95% CI, 48–68%) for the traditional veterinary classification. The frequency of agreement between the LDHp-TPs and the traditional veterinary classification with the true nature of the PEs was significantly different (98% versus 58%, respectively; p<0.0001).

In conclusion, LDHp-TPs has an excellent diagnostic accuracy in discriminate canine PE exudates versus HP-transudates and COP-transudates while the traditional veterinary classification fails.

Disclosures

No disclosures to report.