From the Guidelines
Lactic acid and LDH are distinct entities, with lactic acid being a metabolic byproduct and LDH being an enzyme that catalyzes its conversion, and their measurements serve different purposes in assessing tissue oxygenation, metabolic status, and cellular damage. The key difference between the two lies in their roles and implications in clinical settings. Lactic acid is produced during anaerobic metabolism and can accumulate in the bloodstream, leading to acidosis and symptoms like muscle fatigue 1. On the other hand, LDH is an enzyme that plays a crucial role in energy production pathways and is released when cells are injured or die, making it a marker of tissue damage.
Clinical Significance
- Lactic acid measurement is used to assess tissue oxygenation and metabolic status, with elevated levels indicating oxygen deprivation or metabolic distress.
- LDH measurement is used as a marker of tissue damage, with its five different isoenzymes helping to identify the location of damage in organs like the heart, liver, muscles, lungs, or red blood cells.
- In the context of pleural disease, LDH levels in pleural fluid are used in Light's criteria to differentiate between exudates and transudates, with a pleural fluid LDH divided by serum LDH ratio > 0.6 or a pleural fluid LDH > 2/3 the upper limits of laboratory normal value for serum LDH indicating an exudate 1.
Measurement and Interpretation
- Elevated lactic acid levels typically indicate a need to address oxygenation and metabolic status, potentially through interventions aimed at improving tissue oxygen supply or managing metabolic disorders.
- Elevated LDH levels, particularly in the context of pleural fluid analysis as per the British Thoracic Society guideline 1, suggest the presence of an exudate, which may require specific diagnostic and therapeutic approaches depending on the underlying cause.
From the Research
Difference between Lactic Acid and LDH
- Lactic acid is a product of anaerobic glycolysis, whereas LDH (Lactate Dehydrogenase) is an enzyme that catalyzes the reversible reaction between pyruvate and lactate 2.
- LDH is a group of oxidoreductase isoenzymes with different substrate affinity, inhibition constants, and electrophoretic mobility, playing a key role in cellular, tissue, and organ specificity 2.
- Lactic acidosis, characterized by increased blood lactate concentration and low serum pH, is associated with significant morbidity and mortality in patients with severe sepsis or septic shock 3.
- LDH is a diagnostic biomarker for various diseases, including cancer, thyroid disorders, and tuberculosis, due to its overexpression in different cancers and its role in active metabolism 2, 4.
- Both blood LDH and blood lactate are suggested as risk factors for mortality in patients with serious inflammatory diseases, such as COVID-19 5.
- Elevated lactate levels and systemic acidemia (low blood pH) are associated with increased risk of mortality in patients with cardiogenic shock 6.
Clinical Significance
- LDH isoenzyme levels in serum serve as a significant biomarker for different diseases, including cancer, thyroid disorders, and tuberculosis 2.
- Serum LDH levels are commonly increased in cancer patients and correlated with poor clinical outcome and resistance to therapy 4.
- Lactate formation during sepsis is not entirely related to tissue hypoxia or reversible by increasing oxygen delivery, and its measurement has clinical implications in diagnosis, monitoring, and prognostication in acute and intensive care settings 3.
- LDH inhibitors offer potential applications as therapeutic agents for inflammatory diseases associated with high blood LDH 5.