One of the most commonly performed lab tests, lactate dehydrogenase (LDH, LD) is an enzyme often included in metabolic profiles and liver panels, or ordered separately. Because it is commonly found in heart, liver, muscle, lung and kidney tissue, physicians who suspect pathologies with any of these organs will include LD levels in a laboratory workup.

Because it can be found in almost every cell of the body, it is a non-specific marker for tissue damage. When elevated, more specific tests are usually ordered to determine which organs are involved (e.g., ALT, AST, ALP or LD isoenzymes, which are organ-specific). Since red blood cells are rich in LD, hemolyzed samples cannot be used for testing. Due to its high concentration within red blood cells, LD is often used to diagnose hemolytic anemia. Physicians also order an LD test on cerebrospinal fluid to distinguish between bacterial and viral meningitis.

Because LD is concentrated in muscles, strenuous exercise can be a non-pathological cause for temporary elevations.

LD can be tested on serum (most commonly) or heparinized plasma. Fasting is not required. Samples to be tested for LD must be centrifuged and separated from contact with the LD-rich red blood cells, preferably within two hours. After that, serum levels will be significantly and falsely elevated due to contributions from red blood cells.

LD used to be commonly ordered to diagnose acute myocardial infarction (MI), but has since been replaced in cardiac panels by Troponin.

Bibliography

1. LabTestsOnline. American Association for Clinical Chemistry. AACC. Accessed 9/9/2019.
2. CLSI. Procedures for the Handling and Processing of Blood Specimens for Common Laboratory Tests; Approved Guideline—Fourth Edition. H18-A4. Clinical and Laboratory Standards Institute. Document H18-A4 Wayne, Pennsylvania 2010.
3. Wu A. Tietz Clinical Guide to Laboratory Tests---Fourth Edition. Elsevier. St. Louis, Missouri. 2006.