Elevated Lactate Dehydrogenase (LDH) - Differential Diagnosis Framework LDH is a cytoplasmic enzyme present in tissues throughout the body. • Present in high concentrations in: RBCs, muscle, liver, and kidney • LDH assays can measure the amount of LDH present in the serum that has leaked from the tissues upon damage • Normal range of LDH is between 140 to 280 U/L • It can remain elevated for up to 7 days in the bloodstream Hemolysis: • Hemolytic Anemias: - Spherocytosis, sickle cell disease, deficiency of red blood cell enzymes - Acquired: Microangiopathic hemolytic anemia, PNH, immune hemolysis • Ineffective Erythropoiesis: - Pernicious anemia, folic acid deficiency - Iron deficiency - Primary myelofibrosis • Hemolysis: - Prosthetic valves Lung: • Pneumocystis pneumonia (late) • Tuberculosis • Legionnaires disease • Pulmonary infarction • COVID-19 Pneumonia • Other lung injuries Hepatic Injury: • Early acute hepatitis • Ischemic hepatitis • Acute Hepatocellular Injury - Markedly elevated serum LDH level distinguishes ischemic hepatitis (ALT-to-LDH ratio < 1.5) from viral hepatitis (ALT-to-LDH ratio > 1.5) with a sensitivity and specificity of 94 and 84% Renal: • Renal infarction Muscle: • Rhabdomyolysis • Myopathies (inherited, acquired, drug) • Periodic paralyses CNS Disorders: • Bacterial meningitis • Cerebral hemorrhage • Cerebral venous thrombosis Cardiac: • Myocyte injury • Demand ischemia • Trauma, cardiovascular surgery • Toxins • Infection (myocarditis, rheumatic fever) • Drugs (alcohol, chemotherapy, cocaine, methysergide, carbon monoxide) Malignancy: • Lymphomas • Leukemias • Serum biomarker used in metastatic melanoma • Solid tumors (testicular germ cell tumors) • Tumor lysis syndrome (large tumor burden) Vasculitis: • Polyarteritis nodosa • Eosinophilic granulomatosis with polyangiitis • Granulomatosis with polyangiitis • Behçet's syndrome • Sarcoidosis Idiosyncratic LDH Elevation: • The presence of macro-LDH (LDH combined with an immunoglobulin), not associated with any symptoms or particular disease #LDH #Lactate #Dehydrogenase #Elevated #differential #diagnosis #Laboratory
