[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Lactate dehydrogenase (LDH) as a lab marker [Biochemistry](https://durgical.com/en/biochemistry/) · Topic # Lactate dehydrogenase (LDH) as a lab marker LDH is in almost every cell, so a high blood LDH means tissue damage somewhere. It is sensitive but not specific, and haemolysis in the tube raises it falsely. Updated 2026-11-01 ## Key facts - Reaction: pyruvate + NADH ⇌ lactate + NAD⁺; it regenerates NAD⁺ so glycolysis can keep running without oxygen. - A tetramer of H (LDHB) and M (LDHA) subunits gives five isoenzymes, from LDH-1 (H₄) to LDH-5 (M₄). - LDH-1 predominates in heart and red cells, LDH-3 in lung and LDH-5 in liver and skeletal muscle; the isoenzyme test points to the damaged tissue. - Red cells hold far more LDH than plasma: a haemolysed sample gives a falsely high result (and also raises potassium and AST). - There is no universal normal value: each laboratory sets its own reference range for its method and population. ## In detail - What it measures: total LDH activity in serum, or in pleural, peritoneal or cerebrospinal fluid; electrophoresis separates the five isoenzymes. - Where it comes from: LDH is in nearly all tissues, with the largest amounts in muscle, liver, kidney and red cells; damaged cells release it into the blood. - Main causes of a high LDH: haemolysis (haemolytic anaemias, sickle cell crisis, G6PD crises), megaloblastic anaemia (ineffective red cell production gives very high values), myocardial or lung infarction, liver injury, muscle injury and rhabdomyolysis, pancreatitis, stroke, intestinal ischaemia, infectious mononucleosis, Pneumocystis pneumonia and many cancers. - As a cancer marker it reflects tumour burden and cell turnover (lymphoma, leukaemia, germ-cell tumours, melanoma, tumour lysis); it helps with prognosis and follow-up, not screening. - Pre-analytical traps: haemolysis from a difficult draw, small needles or late separation of serum; strenuous exercise and some drugs also raise LDH. - Reading the pattern: LDH with high indirect bilirubin, low haptoglobin and high reticulocytes suggests haemolysis; with high ALT and AST, the liver; with high CK, muscle. - In pleural fluid, a high fluid-to-serum LDH ratio is one of Light's criteria for an exudate. - A low LDH is rare and usually harmless: large vitamin C intake or an inherited deficiency of one LDH subunit can cause it; LDHA deficiency causes exercise intolerance with myoglobinuria. **Also called** LDH, LD, Lactic acid dehydrogenase, LDH isoenzymes ## Clinical notes - In suspected haemolysis, LDH is ordered with haptoglobin, indirect bilirubin, reticulocytes and a blood smear. - Troponin replaced LDH and its isoenzymes for myocardial infarction; LDH rises late (after about a day) and stays high for a week or more. - A high LDH in a person with HIV and diffuse lung infiltrates supports Pneumocystis pneumonia. - In lymphoma and testicular germ-cell tumours, LDH helps estimate prognosis and follow the response to treatment. ## Pathways - [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/) ## Related conditions - [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/) - [Rhabdomyolysis](https://durgical.com/en/conditions/rhabdomyolysis/) - [Glucose-6-phosphate dehydrogenase (G6PD) deficiency](https://durgical.com/en/conditions/glucose-6-phosphate-dehydrogenase-deficiency/) - [Sickle cell disease](https://durgical.com/en/conditions/sickle-cell-disease/) - [Megaloblastic anaemia (B12 or folate deficiency)](https://durgical.com/en/conditions/megaloblastic-anaemia/) - [Infectious mononucleosis](https://durgical.com/en/conditions/infectious-mononucleosis/) - [Pneumocystis pneumonia (PCP)](https://durgical.com/en/conditions/pneumocystis-pneumonia/) - [Testicular cancer](https://durgical.com/en/conditions/testicular-cancer/) - [Tumour lysis syndrome](https://durgical.com/en/conditions/tumour-lysis-syndrome/) - [Acute pancreatitis](https://durgical.com/en/conditions/acute-pancreatitis/) ## Related - [Lactate](https://durgical.com/en/biochemistry/molecules/lactate/) - [Pyruvate](https://durgical.com/en/biochemistry/molecules/pyruvate/) - [Glycolysis](https://durgical.com/en/biochemistry/pathways/glycolysis/) - [NAD⁺ (nicotinamide adenine dinucleotide)](https://durgical.com/en/biochemistry/molecules/nad/) - [Isoenzymes](https://durgical.com/en/biochemistry/topics/isoenzymes/) - [Creatine kinase (CK) and CK-MB as lab tests](https://durgical.com/en/biochemistry/topics/creatine-kinase-and-ck-mb-as-lab-tests/) - [Cardiac troponin as a lab test](https://durgical.com/en/biochemistry/topics/cardiac-troponin-as-a-lab-test/) - [Aminotransferases (ALT and AST) as lab tests](https://durgical.com/en/biochemistry/topics/aminotransferases-as-lab-tests/) - [Liver function tests: reading the pattern](https://durgical.com/en/biochemistry/topics/liver-function-tests-reading-the-pattern/) - [Tumour markers: principles of use](https://durgical.com/en/biochemistry/topics/tumour-markers-principles-of-use/) - [Cori cycle](https://durgical.com/en/biochemistry/topics/cori-cycle/) - [Warburg effect (aerobic glycolysis in cancer)](https://durgical.com/en/biochemistry/topics/warburg-effect/) ## Test yourself Think of the answer, then tap the question to see it. ## What reaction does lactate dehydrogenase catalyse, and why does it matter in hypoxia? Pyruvate + NADH ⇌ lactate + NAD⁺; regenerating NAD⁺ lets glycolysis keep making ATP when oxygen is lacking. ## Why can a haemolysed blood sample show a falsely high LDH? Red cells contain much more LDH than plasma; when they break in the tube they release it, along with potassium and AST. ## Which LDH isoenzyme predominates in the heart and red cells? LDH-1 (four H subunits, from the LDHB gene); LDH-5 (four M subunits) predominates in liver and skeletal muscle. ## Which lab findings together point to haemolysis as the cause of a high LDH? High indirect bilirubin, low haptoglobin and high reticulocytes, ideally with a blood smear showing damaged red cells. ## Why does megaloblastic anaemia often give a very high LDH? Many abnormal red cell precursors die in the bone marrow (ineffective erythropoiesis) and release their LDH. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/lactate-dehydrogenase-as-a-lab-marker/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Lactate Dehydrogenase (LDH) Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/lactate-dehydrogenase-ldh-test/) (MedlinePlus, US National Library of Medicine, 2026); [Lactate dehydrogenase test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003471.htm) (MedlinePlus, US National Library of Medicine, 2026); [LDH isoenzyme blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003499.htm) (MedlinePlus, US National Library of Medicine, 2026); [LDHA: L-lactate dehydrogenase A chain (human)](https://www.uniprot.org/uniprotkb/P00338/entry) (UniProt, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011). [← All of biochemistry](https://durgical.com/en/biochemistry/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/biochemistry/topics/lactate-dehydrogenase-as-a-lab-marker/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/lactate-dehydrogenase-as-a-lab-marker/