Macromolecular Lactate Dehydrogenase: An Innocent Bystander

Summary Lactate dehydrogenase (LD) activity is often increased in malignancy, and may occasionally be a useful tumor marker. In the case reported here, a persistently increased LD activity led to an extensive search for a neoplasm. Results of routine investigations were normal, but LD electrophoresis followed by gel filtration and immunofixation confirmed the presence of a circulating macromolecular LD, comprising IgA K bound to LD. Altogether it may provoke unnecessary investigations, the LD-IgA complex currently has no diagnostic significance.