Lactic Acid and Lactate Dehydrogenase in Clinical Diagnosis

Clinical Significance of LDH

The European Respiratory Society recommends using LDH levels to distinguish between transudative and exudative pleural effusions, with a sensitivity of 98% and specificity of 72% 1
Elevated LDH levels are associated with high tumor burden in conditions like plasma cell leukemia, according to the European Hematology Association 2
The British Thoracic Society suggests that pleural fluid LDH >0.67 of the upper limit of normal serum value helps identify exudates 3
LDH is included in Light's criteria to differentiate exudates from transudates, with a pleural fluid LDH divided by serum LDH ratio of >0.6 or pleural fluid LDH >2/3 the upper limit of normal serum LDH 4, 3

Elevated LDH is associated with poor prognosis in plasma cell leukemia, with a high tumor burden and aggressive disease course 2
The International Prognostic Score for Hodgkin's disease includes LDH as a prognostic factor, according to the British Journal of Cancer 5

LDH is commonly measured in clinical laboratories as an indicator of tissue damage, with enzymatic activity affected by pH and components in the culture medium 6, 7, 8
LDH release assays are used to detect cell death by measuring the enzymatic activity of LDH released into culture supernatants or body fluids following plasma membrane breakdown 6, 7

LDH is also referred to as lactic acid dehydrogenase, and the test may be ordered simply as “LDH” or “total LDH.” 9
The abbreviation “LDH” is the standard term used universally in clinical laboratories and medical literature. 10

Total LDH measurement reflects the combined enzymatic activity from all tissue sources. 9
LDH isoenzyme (fraction) analysis can be requested when identification of the tissue origin of elevation is needed, although this is ordered less frequently. 9
Serum LDH or plasma LDH specifications indicate the type of specimen used for the assay. 10

LDH activity is quantified by spectrophotometric monitoring of the reversible conversion of lactate to pyruvate (or vice‑versa) using NAD⁺/NADH as a co‑enzyme. 9

LDH serves as a nonspecific biomarker of tissue injury and cell death, with applications in the evaluation of pleural effusions, cancer prognosis, and various inflammatory conditions. 11

The upper limit of normal for LDH is highly laboratory‑specific and depends on the assay conditions employed. 9

The European guideline on trauma management recommends using blood lactate as a sensitive test to estimate and monitor the extent of bleeding and tissue hypoperfusion in trauma patients. 12
The same European trauma guideline advises that serial LDH measurements can be used to objectively evaluate a patient’s response to therapy during shock states. 12

In trauma patients who have consumed alcohol, the reliability of lactate determination may be reduced, potentially affecting the interpretation of hypoperfusion assessment. 12