Association of an oxygen-sensitive lactate dehydrogenase isoenzyme, LDk, with LD-6 in serum of critically ill patients.

We measured a highly unusual, oxygen-sensitive lactate dehydrogenase, LDk, in the serum of six patients whose serum showed a band for LD-6 on routine agarose gel electrophoresis for LD isoenzymes. All these patients showed very high serum LDk activity, greatly exceeding the high values previously described in serum of patients with various malignant tumors. In two of the patients, LDk activity was low both before LD-6 was found in and after it disappeared from the serum, evidencing a correlation with LD-6. All of the six patients, five of whom died in the hospital, had severe hypotension. We suggest that hypoxia is responsible for the appearance of LD-6 in serum and that LD-6 is found in association with high LDk activity in serum of critically ill patients.