Lactate dehydrogenase: an old enzyme reborn as a COVID-19 marker (and not only).

Background Historically, the lactate dehydrogenase (LDH) measurement was introduced into Laboratory Medicine as component (together with creatine kinase (CK) and aspartate aminotransferase) of the classical enzyme triad employed for the diagnosis of myocardial infarction, which was subsequently replaced by CK-MB, and more recently by cardiac troponins. Afterwards, for many years, the clinical application of serum LDH measurement has been limited to the evaluation of anemias and to as a rough prognostic tool for certain tumors. Content In the last few years, significant changes have happened. First, the test has been confirmed as a robust predictor of poor outcomes in many neoplastic conditions. Furthermore, in the Revised International Staging System adopted in the 2015 by the International Myeloma Working Group, LDH acts as determinant of disease biology in differentiating myeloma stages. Finally, in the last few months, LDH is definitively reborn given its proven significant contribution in defining the COVID-19 severity. Conclusions This increased clinical role calls for an improvement of LDH assay standardization through the implementation of traceability of results of clinical samples to the available reference measurement system.