eng Science and Education Publishing American Journal of Medical Case Reports 2374-216X 2024-01-29 12 1 6 9 10.12691/ajmcr-12-1-2 AJMCR20241212 article Patrik Wintersberger patrik.wintersberger@gmx.at 1 2 Jščrgen Harauer 2 Karl Landsteiner Privatuniversit?t fščr Gesundheitswissenschaften, Krems, Austria Lactate dehydrogenase (LDH) is an unspecific marker predominantly for hemolysis, thrombotic, infectious, and malignant diseases. On rare occasions, it can also be idiosyncratically elevated. We present a case of a 30-year-old otherwise healthy female patient who is referred to outpatient internal medicine with a persistent LDH elevation for years. Extensive laboratory and radiological diagnostics are performed without any indications of disease. Macro-LDH is suspected, and serum immunocomplex precipitation with polyethylene glycol is performed. Laboratory results make the presence of macro-LDH likely. Therefore, it is suggested that macroenzymes be considered early in the diagnostic journeys of patients with elevated serum enzyme activities unsuitable to the corresponding clinical context to spare them unnecessary procedures and provide them with a diagnosis of this probable benign condition. https://pubs.sciepub.com/ajmcr/12/1/2/ajmcr-12-1-2.pdf lactate dehydrogenase macroenzymes macro-LDH PEG precipitation idiosyncratic LDH elevation