Test Catalog

Test ID: LDBF    
Lactate Dehydrogenase (LDH), Body Fluid

Useful For Suggests clinical disorders or settings where the test may be helpful

Identification of exudative pleural effusions


Lactate dehydrogenase in pericardial fluids is not diagnostically useful.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Lactate dehydrogenase (LDH) activity is present in all cells of the body with the highest concentrations in the heart, liver, muscle, kidney, lung, and erythrocytes.


Pleural fluid:

Pleural fluid is normally present within the pleural cavity surrounding the lungs, serving as a lubricant between the lungs and inner chest wall. Pleural effusion develops when the pleural cavity experiences an overproduction of fluid due to increased capillary hydrostatic and osmotic pressure that exceeds the ability of the lymphatic or venous system to return the fluid to circulation. Laboratory-based criteria are often used to classify pleural effusions as either exudative or transudative. Exudative effusions form due to infection or inflammation of the capillary membranes allowing excess fluid into the pleural cavity. Patients with these conditions benefit from further investigation and treatment of the local cause of inflammation. Transudative effusions form due to systemic conditions such as volume overload, end stage renal disease, and heart failure that can lead to excess fluid accumulation in the pleural cavity. Patients with transudative effusions benefit from treatment of the underlying condition.(1) Measurement of LDH in body fluids is primarily indicated to aid in the differentiation of transudative and exudative effusions as LDH activity is considered an indicator of the extent of inflammation. Dr. Richard Light derived criteria in the 1970s for patients with pleural effusions that are still used today.(2)


The criteria include the measurement of total protein and LDH in pleural fluid and serum. Exudates are defined as meeting one of the following criteria:

1. Pleural fluid-to-serum protein ratio above 0.5

2. Pleural fluid LDH above two-thirds the upper limit of normal serum LDH

3. Pleural fluid-to-serum LDH ratio above 0.6


Pericardial fluid:

The routine analysis of LDH to differentiate exudative and transudative pericardial effusions is not considered helpful.(3)


Peritoneal fluid:

Spontaneous bacterial peritonitis or ascitic fluid infection is common (12%) at the time of admission of a patient with cirrhosis and ascites. The diagnosis is made in the presence of an elevated ascitic fluid absolute polymorphonuclear (PMN) leukocyte count (ie, >250 cells/mm(3) [0.25 x 10(9)/L]) without an evident intra-abdominal, surgically treatable source of infection.(4)


Secondary bacterial peritonitis (ie, ascitic fluid infection caused by a surgically treatable intra-abdominal source) can masquerade as spontaneous bacterial peritonitis. Signs and symptoms do not help separate patients who need surgical intervention from those who have spontaneous bacterial peritonitis and need only antibiotic treatment. In contrast, the initial ascitic fluid analysis and the response to treatment can assist with this important distinction. The characteristic analysis in the setting of free perforation is PMN count of 250 cells/mm(3) (usually many thousands) or higher, multiple organisms (frequently including fungi and enterococcus) on Gram stain and culture, and at least 2 of the following criteria: total protein above 1 g/dL, LDH above the upper limit of normal for serum, and glucose below 50 mg/dL. Studies have reported higher than 95% sensitivity but low specificity using these criteria; a computerized tomographic scan was diagnostic in 85% of patients with secondary peritonitis.(5)

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation Provides information to assist in interpretation of the test results

Pleural fluid lactate dehydrogenase (LDH) to serum LDH ratio above 0.6 are most consistent with exudative effusions.(2,6)


Peritoneal fluid LDH above 220 U/L suggests secondary, rather than spontaneous bacterial peritonitis, in conjunction with other laboratory, imaging, and clinical findings.(4,5)


Synovial fluid LDH may be elevated greater than plasma or serum LDH due to inflammatory causes. Values should be interpreted in conjunction with other clinical findings.(7)


All other fluids: LDH may be used to differentiate transudative from exudative effusions. The decision limits are not well defined in fluids other than pleural fluid and should be interpreted in conjunction with other clinical findings.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Lactate dehydrogenase (LDH) activity is one of the most sensitive indicators of in vitro hemolysis. Causes can include transportation via pneumatic tube and vigorous mixing.


Contamination with erythrocytes will elevate results, because the analyte level in erythrocytes is higher than in normal sera. The level of interference may be variable depending on the content of analyte in the lysed erythrocytes.


In very rare cases of gammopathy, in particular Waldenstrom macroglobulinemia, type IgM, may cause unreliable results.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Block DR, Florkowski CM: Body fluids. In: Rafai N, Horvath AR, Wittwer CT. eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018:chap 43

2. Light RW, Macgregor I, Luchsinger PC, Ball WC: Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med. 1972;77:507-513

3. Ben-Horin S, Bank I, Shinfeld A, et al: Diagnostic value of the biochemical composition of pericardial effusions in patients undergoing pericardiocentesis. Am J Cardiol. 2007;99(9):1294-1297

4. Soriano G, Castellote J, Alvarez C, et al: Secondary bacterial peritonitis in cirrhosis: a retrospective study of clinical and analytical characteristics, diagnosis and management. J Hepatol. 2010 Jan;52(1):39-44

5. Sahn, SA: Getting the most from pleural fluid analysis. Respirology. 2012;17:270-277

6. Tarn AC, Lapworth R: Biochemical analysis of ascitic (peritoneal) fluid: what should we measure? Ann Clin Biochem. 2010;47:397-407

7. Pejovic M, Stankovic A, Mitrovic DR: Lactate dehydrogenase activity and its isoenzymes in serum and synovial fluid of patients with rheumatoid arthritis and osteoarthritis. J Rheumatol. 1992;19:529-533

8. Nandakumar V, Dolan C, Baumann NA, et al: Effect of pH on the quantification of body fluid analytes for clinical diagnostic testing. Am J Clin Path. 2019 Oct; 152(1):S10-S11