Significance of isolated increases in total lactate dehydrogenase and its isoenzymes in serum of patients with bacterial pneumonia.

Total lactate dehydrogenase (LD, EC 1.1.1.27) activity in serum and LD isoenzymes were quantified at the time of diagnosis in 320 patients with bacterial pneumonia. In eighty, LD activity was increased, but this was accompanied by either other pathological results for liver-function tests or associated diseases that could explain it. The remaining 240 patients were divided into four groups, based on their total serum LD values: group A, less than 225 U/L (normal limit); group B, 226-350 U/L; group C, 351-499 U/L; and group D, greater than 500 U/L. Total LD was above normal at diagnosis in 40% of the patients. Recovery time was twice as long in group D as in groups A, B, and C. In five patients from group D, the pneumonia reflected underlying lung cancer. In groups B and C, the LD-3 ratio was increased in comparison with group A; in group D, LD-4 and LD-5 were increased up to twice the normal limit. Evidently nearly half of patients with bacterial pneumonia may show isolated increases in total LD activity (mostly LD-3) in serum. In cases with high activity, prolonged recovery time is expected. Intensive follow-up and extensive investigation are warranted in these patients, because some may have underlying lung cancer.