Abstract
Background: Lactate dehydrogenase (LDH) isoenzymes may be useful in the differential diagnosis of pleural effusion (PE) and ascitic fluid (AF) aetiologies in cats since tissue damage induces their release, changing the pattern of their activity.
Aim: The present study aimed to determine the diagnostic utility of measuring lactate dehydrogenase levels and isoenzyme activities in PE or AF in cats with malignancy.
Materials and Methods: The results of LDH levels and isoenzyme activities in the serum, PE and AF of 29 cats were compared among malignant group, infectious group, and non-malignant, non-infectious group. A receiver operating characteristic (ROC) analysis was performed to assess the accuracy in diagnosing feline malignancy.
Results: In PE or AF, there were significant differences in LDH level and LDH isoenzyme activities among the three groups. The combination of LDH level and LDH-1 activity in PE or AF had the highest area under the ROC (AUC) values for discriminating malignant effusion from non-malignant effusion. The AUC of the combination of LDH level and LDH-1 activity in PE or AF was 0.874. The sensitivity and specificity of using the combination of LDH level (cut-off: <2,269 U/L) and LDH-1 activity (cut-off: <4.8%) in PE or AF for predicting malignancy with the highest AUC value were 94.4% and 72.7%, respectively.
Conclusion: Our results suggest that the combination of LDH level and LDH-1 activity in PE or AF is a potential factor for diagnosing malignancy. Considering that LDH isoenzymes can be measured inexpensively and easily, LDH tests can be readily accommodated in veterinary clinical practice.

Key words: ascitic fluid, cat, lactate dehydrogenase isoenzymes, malignancy, pleural effusion