The utility of lactate dehydrogenase isoenzyme pattern in the diagnostic evaluation of malignant and nonmalignant ascites.

Objective: Lactate dehydrogenase (LDH), a tetrameric protein composed of four monomers, is expressed as five isoenzymes. Serum LDH isoenzymes may be useful in differential diagnosis of ascites etiology since tissue damage releases isoenzymes contained therein, leading to a change in their pattern.
Materials and Methods: We determined ascitic fluid LDH level and LDH isoenzyme activities in patients with malignant and nonmalignant ascites in a total of 76 patients (43 males and 33 females).
Results: LDH level, LDH-4 activity and LDH-5 activity were found to be significantly higher, and LDH-1 activity was found to be lower in malignant ascites when compared with nonmalignant ascites. LDH-1 activity was detected to be significantly higher in the sterile cirrhotic ascites when compared with spontaneous bacterial peritonitis, malignant ascites, tuberculous ascites and congestive heart failure-related ascites. LDH-2 activity was found to be higher in spontaneous bacterial peritonitis when compared with the other groups. LDH-3 activity was detected to be higher in spontaneous bacterial peritonitis, malignant ascites and tuberculous ascites when compared with the sterile cirrhotic ascites. In the diagnosis of malignant ascites, the sensitivity and specificity were 96% and 76% for LDH level, 90% and 70% for LDH-1 activity, 94% and 62% for LDH-4 activity, and 100% and 56% for LDH-5 activity, respectively.
Conclusion: Ascitic LDH and its isoenzyme pattern may be helpful for the differential diagnosis of the most common causes of ascites: cirrhosis, spontaneous bacterial peritonitis, congestive heart failure, tuberculosis and malignancy.