Highly elevated lactate dehydrogenase level in a healthy individual: a case of macro-LDH.

Macroenzymes are complexes of serum enzymes with a plasmatic protein. They have a higher molecular weight and a more prolonged serum half-life than those of unbound enzymes. Although macroenzymes may be found in the serum of post-myocardial infarction patients, they are not usually associated with any specific disease. Their presence, however, can cause an elevation in the serum levels of an enzyme, possibly leading to errors in diagnosis. We report a patient with extremely elevated serum levels of lactate dehydrogenase (LDH) due to the formation of complexes with immunoglobulin G. She had undergone a myriad of clinical examinations until the macroenzyme responsible for this finding was detected. We also review the literature on the clinical significance of macro-LDH. We propose that awareness of this rare and probably benign phenomenon can spare the patient from the distress of exhaustive investigations.