Background: Serum lactate dehydrogenase (LDH) is elevated in various diseases. 

Objectives: To analyze serum LDH as a distinguishing clinical biomarker and as a predictor of in-hospital outcome in admitted medical patients.

Methods: We analyzed a cohort of all 158 patients with very high isolated LDH (LDH ≥ 800 IU/ml – without concomitant elevations of alanine aminotransferase and aspartate aminotransferase) – admitted to our internal medicine department during a 3 year period. Epidemiologic and clinical data, as well as the final diagnosis and outcome were recorded and compared with those of a cohort of all 188 consecutive control patients.

Results: Very high isolated LDH was a distinguishing biomarker for the presence of cancer (27% vs. 4% in the LDH group and controls respectively, P < 0.0001), liver metastases (14% vs. 3%, P < 0.0001), hematologic malignancies (5% vs. 0%, P = 0.00019), and infection (57% vs. 28%, P < 0.0001). Very high isolated LDH was a marker for a severe prognosis, associated with more admission days (9.3 vs. 4.1, P < 0.0001), significantly more in-hospital major complications, and a high mortality rate (26.6% vs. 4.3%, P < 0.0001). Finally, very high isolated LDH was found in a multivariate regression analysis to be an independent predictor of mortality.

Conclusions: The presence of very high isolated LDH warrants thorough investigation for the presence of severe underlying disease, mostly metastatic cancer, hematologic malignancies and infection. Moreover, it is a marker for major in-hospital complications and is an independent predictor of mortality in admitted medical patients.