Lactate dehydrogenase isoenzymes in human prostatic fluid: an aid in recognition of malignancy?

A total of 1,435 specimens of prostatic fluid were collected from 1,076 patients by rectal massage. Lactate dehydrogenase isoenzymes in the fluid were separated by acrylamide disk electrophoresis and the ratio of lactic dehydrogenase-5/lactic dehydrogenase-1 was used as the parameter for the test. There were significant differences in the ratio among patients with a normal prostate, benign prostatic hyperplasia and prostatic carcinoma. The mean values of lactic dehydrogenase-5/lactic dehydrogenase-1 ratios were 0.48 +/- 0.09, 1.36 +/- 0.17 and 5.21 +/- 0.79, respectively. Of 30 patients with histological evidence of prostatic carcinoma 25 (85 per cent) had a ratio greater than 2 in the prostatic fluid. On the other hand the ratio was less than 2 in 50 of 57 men (88 per cent) with a histological diagnosis of benign prostatic hyperplasia devoid of inflammation. When prostatic fluid contained white blood cells a positive correlation was observed between the ratio and the number of white blood cells per microscopic field (r equals 0.289, p less than 0.001). The results indicate that a lactic dehydrogenase-5/lactic dehydrogenase-1 ratio exceeding 2 in the prostatic fluid in the absence of inflammation should be regarded as an indication of high risk of the presence of carcinoma of the prostate.