A sixth lactate dehydrogenase isoenzyme (LD6) and its significance.

We have seen 11 patients who had a sixth cathodic band on routine lactate dehydrogenase (LD) electrophoresis of their serum specimens. This isoenzyme is heat stable and does not cross-react with any of the immunoglobulins; hence, it is not an immunoglobulin complex. An electrophoretic pattern of a liver extract obtained at the time of autopsy of one of these patients disclosed the LD6 band, thus verifying its origin or clearance in the liver. It was not seen in the heart extract of the same patient. Although no specific disease entity could be etiologically related to its presence, we noted that seven of the 11 patients had known arteriosclerotic cardiovascular disease, eight had had cardiogenic, septic, or hemorrhagic shock during their hospitalization, all had mildly to notably elevated levels of LD5 (implying at least acute hepatic congestion), and seven died during their hospitalization or shortly after discharge. The remaining four patients were still living one to two years later. However, we concluded that the presence of LD6 signifies a poor prognosis for the patient.