Evaluation of Serum Levels of Lactate Dehydrogenase Isoenzymes in COVID- 19 Patients

Background: This study aimed to determine the serum levels of lactate dehydrogenase isoenzymes (LDH1, LDH2, LDH3, LDH4, and LDH5) and their contribution to the total lactate dehydrogenase enzyme elevation observed in COVID-19 patients. Design of study: This study was conducted in collaboration between Al-Nahrain University/College of Medicine/Chemistry and Biochemistry Department and Al- Yarmouk Teaching Hospital, Baghdad, Iraq. The study included 90 patients with confirmed COVID-19 infection: 45 with severe symptoms, and 45 with mild symptoms during the period from February 2021 to June 2021. The different LDH isoenzymes (LDH1, LDH2, LDH3, LDH4, and LDH5) were determined by enzyme-linked immunosorbent assay (ELISA) kits. Results: This study showed high correlation between total lactate dehydrogenase (LDH) enzyme and disease progression and severity in patients with COVID-19. The study also showed significantly higher levels of the lactate dehydrogenase isoenzymes (LDH1, LDH3, and LDH4) in patients with severe symptoms. Conclusion: This study suggests that elevation of serum lactate dehydrogenase (LDH) in patients with COVID-19 may be associated with the release of more than one of LDH isoenzymes into the bloodstream, therefore the use of total LDH as a specific biomarker for lung affectation in patients with COVID-19 is not specific, but the assay of all LDH isoenzymes could give a better understanding of the tissues most affected by the virus.