Diagnostic utility of measuring lactate dehydrogenase levels and its isoenzyme activities for the evaluation of malignancy in feline pleural effusion and ascitic fluid

Lactate dehydrogenase (LDH) isoenzymes may be useful in the differential diagnosis of pleural effusion (PE) and ascitic fluid (AF) etiologies in cats since tissue damage induces their release, thereby changing the pattern of their activity. The present study aimed to determine the diagnostic utility of measuring LDH levels and its isoenzyme activities in PE or AF in cats with malignancy. We measured LDH levels and its isoenzyme activities in serum, PE, and AF in 29 cats and compared the results between malignant, infectious diseases, and non-malignant, non-infectious diseases. Receiver operating characteristic (ROC) analysis was performed to assess the accuracy of the tests in diagnosing feline malignancy. In PE or AF, significant differences were found in LDH levels and LDH isoenzymes 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) value of 0.874 for discriminating malignant effusion from non-malignant effusion. The sensitivity and specificity of using the combination of LDH level (cutoff: <2,269 U/L) and LDH-1 activity (cutoff: <4.8%) in PE or AF for predicting malignancy with the highest AUC value were 94.4% and 72.7%, respectively. Our results suggest that the combination of LDH level and LDH-1 activity in PE or AF can potentially diagnose for malignancy. Considering that LDH isoenzymes can be measured inexpensively and easily, LDH tests can be readily accommodated in veterinary clinical practice.