Diagnostic value of ascitic fluid lactic dehydrogenase, protein, and WBC levels

Three characteristics of an exudate, ie, an ascitic fluid lactic dehydrogenase (LDH) level of greater than 400 Sigma units (SU), an ascitic fluid-serum LDH ratio of greater than 0.6, and an ascitic fluid-serum protein ratio of greater than 0.5, were studied in a prospective fashion to determine their usefulness in the differential diagnosis of ascites. The ascitic fluid LDH level did not exceed 400 SU in any patient with uncomplicated chronic liver disease, whereas in patients with malignant, tuberculous, or pancreatic ascites it exceeded 500 SU in 12/19 patients. The finding of two of the three characteristics indicated a nonhepatic cause for the ascites whereas the absence of all three strongly suggested uncomplicated liver disease as the sole cause. The ascitic fluid WBC count was also useful in that values exceeded 500/cu mm in bacterial and tuberculous peritonitis whereas it was low (297 +/- 49/cu mm) in chronic liver disease.