LDH blood test: normal levels, high causes, and next steps

LDH (lactate dehydrogenase) is an energy enzyme found inside almost every cell in your body, with the largest amounts in muscle, liver, kidneys and red blood cells. When cells are damaged or burst, LDH spills into your blood. That makes LDH a sensitive, all-purpose alarm for cell damage. The tests next to it on your report tell you where the damage is.¹²

The short version

• Normal: check the range on your report. Most adult ranges top out around 220 to 226 U/L: Oxford University Hospitals uses 125–220, and Labcorp uses 121–224 for men and 119–226 for women. Children run higher.³⁴
• Mildly high usually means cells somewhere are breaking open faster than usual: a hard workout, red blood cells breaking down (hemolysis), or an irritated liver. A blood sample that was shaken or handled roughly can also read high, because red cells burst in the tube.¹⁵⁶
• Very high results come with serious illness. Labcorp lists megaloblastic anemia, widespread cancer and shock among the causes of the highest levels. In pregnancy, LDH over 600 U/L with low platelets and high liver enzymes is the lab signature of HELLP syndrome, which needs care right away.⁴⁷
• LDH tells you that cells are damaged. Where comes from its neighbors: haptoglobin and bilirubin for red cells, CK for muscle, ALT for liver.⁸⁵⁹

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What LDH is

LDH is one of the enzymes your cells use to make energy from sugar. It turns a molecule called pyruvate into lactate, and lactate back into pyruvate. Skeletal muscle runs the reaction toward lactate during hard exercise. The heart runs it the other way and burns lactate as fuel.¹⁰² (More on the chemistry at the end.)

Because nearly every cell carries LDH, the level in your blood is the sum of many small leaks from all over the body. Red blood cells matter most in practice: they are packed with LDH, so anything that breaks them, inside your body or inside the tube, pushes the number up.⁸⁶

LDH and lactate (lactic acid) are two different tests. Lactate is the molecule; LDH is the enzyme that makes and uses it. Clinicians order LDH to look for tissue damage, to check for hemolysis, and to follow some cancers and infections. No fasting or other preparation is needed.¹

What's a normal LDH?

Start with the range printed on your own report. LDH methods use different reagents and reaction directions, so each lab sets its own range.²

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• Oxford University Hospitals in the UK uses 125–220 IU/L for adults of both sexes.³
• Labcorp, a large US commercial lab, uses 121–224 U/L for men and 119–226 U/L for women over 17.⁴
• A Danish hospital lab that recalculated its range from routine results in 2018 found 127–240 U/L. The older Nordic limit of 205 U/L flagged 25.1% of all its LDH results as high, and the authors argued it should be raised.¹¹

Children run higher. Labcorp's upper limit is 361 U/L for boys aged 1 to 3 (352 for girls), and it falls to adult levels by the late teens.⁴ Adult men and women are close: Labcorp's adult limits for the two differ by only 2 U/L.⁴

"Optimal" LDH: what health optimizers aim for

Functional-medicine practitioners aim for a narrower band inside the lab range. Here's the full ladder, from strictest to loosest:

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Where the outcome evidence comes from. The strongest studies linking LDH to outcomes were done in people who were already sick:

• In a pooled analysis of 76 studies and 22,882 people with cancer, mostly advanced, a high LDH (the median cutoff was 245 U/L) went with a 70% higher risk of death (hazard ratio 1.7).¹⁴
• In 213 adults with sickle cell disease, LDH tracked how fast red cells were breaking down. It rose with AST, bilirubin and young red cells (reticulocytes), and it rose as haptoglobin fell.¹⁵

For healthy people, bands like 140–180 come from functional-medicine practice rather than from outcome trials.¹²¹³

Keep "optimal" in perspective. A result of 195 sits above the app's optimal band and inside every lab range on this page. That's a reason to think about last week's workouts and to look at the neighbors, and it is far from a diagnosis. Pushing LDH lower is no goal in itself either: a low LDH is uncommon and usually harmless.¹

What a high LDH usually means

The first question is where the extra LDH is coming from, and the size of the rise is the first hint. Labcorp groups the causes by how high LDH usually goes:⁴

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Mildly high: common, usually explained by the neighbors

The usual suspects:

• A hard workout or a muscle strain. After one hour of weightlifting, LDH in healthy young men peaked about 3 days later and was still above their starting level a week later. CK and AST rose even further above their limits.⁵ A half marathon raised LDH 1.3-fold, and it was still raised 24 hours later.¹⁶
• A sample problem. Red cells hold a lot of LDH. If they burst in the tube, after a difficult draw or rough handling, LDH reads falsely high. In one lab study, hemolysis too faint to see still shifted LDH, AST and potassium enough to matter.⁶ Labs reject grossly hemolyzed samples, and the fix is a clean redraw.⁴⁶
• Red blood cells breaking down in the body (hemolysis). Autoimmune hemolytic anemia, sickle cell disease and leaking mechanical heart valves are examples. LDH rises only slightly when damaged red cells are cleared by the spleen and liver, and to 4 to 5 times the upper limit when they burst inside the blood vessels.⁸¹⁵
• Liver disease. Hepatitis, cirrhosis and other liver disease can raise LDH, usually alongside a much bigger rise in ALT and AST.²⁴ In acute viral hepatitis, LDH is up in about half of people, and only slightly.⁹
• Medicines. Some medicines can raise LDH.¹ Don't stop a prescribed medicine on your own. Bring your full list to your clinician.
• Less common but important: lung disease (pneumonia, a blood clot in the lung), kidney disease, pancreatitis, fractures, heart damage, severe B12 deficiency and other megaloblastic anemias, and some cancers. LDH helps gauge how serious lymphoma, leukemia, myeloma, melanoma and testicular cancer are.²⁴¹

A big number still needs its neighbors. In one hospital, 312 people had an LDH more than 3 standard deviations above normal. Only 9 had the cancers LDH is formally used to stage (melanoma and germ-cell tumors); the rest had other cancers, long-term illnesses or sepsis.¹⁷

Very high: serious illness

Labcorp lists megaloblastic anemia, widespread cancer and shock among the causes of the highest LDH levels.⁴ At that level, LDH is one clue among many, and the other results and symptoms lead.

Get prompt care if a high LDH comes with dark, red-brown urine and muscle pain or weakness after exertion (a sign of muscle breakdown), or with yellow skin or eyes.¹⁰⁹ If you're in late pregnancy or just gave birth, pain under the right ribs, nausea, vomiting, yellowing or confusion needs same-day care: LDH over 600 U/L with low platelets and high AST or ALT is how HELLP syndrome is diagnosed.⁷

LDH reads best next to its neighbors

LDH says cells are damaged somewhere. The pattern across the rest of your results usually says where:⁸⁵⁹

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Two more neighbors help with red cells: a reticulocyte count (young red cells, which rise as the marrow replaces lost cells) and a blood smear.⁸ For the heart, clinicians use troponin, which has mostly replaced LDH tests for diagnosing heart attacks.²⁰

Is a low LDH a problem?

Usually not. A low LDH is uncommon and is rarely a health problem. Large doses of vitamin C or vitamin E can lower the result.¹⁴

A rare inherited condition, LDH deficiency, affects about 1 in a million people in Japan. One type (LDH-A) causes fatigue, cramps and muscle pain during exercise, and sometimes muscle breakdown. The other type (LDH-B) causes no symptoms and turns up by chance on routine blood tests.¹⁰

How fast LDH changes

After muscle strain, LDH peaks and clears sooner than CK, AST or ALT. After one hour of weightlifting, LDH crossed the upper limit at a median of 26 hours, peaked at 78 hours and was back under the limit by 142 hours (about 6 days). CK, AST and ALT were still above their limits on day 7.⁵

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What that means in practice:

• Mention recent exercise, injuries and illness when you get tested. A hard session in the past week can still show up.⁵¹⁶
• Your own LDH is steady. In 91 healthy adults tested weekly for 10 weeks, LDH varied about 5.2% within a person, versus 12.6% between people.²¹ Your trend against your own baseline says more than one result against a population range.
• Repeat a surprising high with a clean draw, from the same lab if you can, because methods differ between labs.⁶²

Going deeper: five forms of LDH

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LDH moves hydrogen between pyruvate and lactate using the carrier NADH/NAD+. Each LDH molecule is built from four subunits of two kinds, A and B. The all-A form sits mostly in skeletal muscle and makes lactate during hard exercise. The all-B form sits mostly in the heart and turns lactate back into pyruvate for fuel.¹⁰²

Mixing A and B gives five forms, LDH-1 to LDH-5. LDH-1 is mainly in the heart and red blood cells, LDH-2 in white blood cells, LDH-3 in the lungs, LDH-4 in the kidneys, pancreas and placenta, and LDH-5 in the liver and skeletal muscle.²⁰ An isoenzyme test separates them: LDH-1 higher than LDH-2 can point to a type of anemia, and LDH-5 higher than LDH-4 to the liver.²⁰ In sickle cell disease, the extra LDH is mostly LDH-1 and LDH-2, the red-cell forms.¹⁵

The ALT-to-LDH ratio sorts sudden liver injuries. In a study of 97 people with ALT or AST at least 5 times the upper limit, the average ratio was 4.65 in viral hepatitis, 0.87 in shock liver and 1.46 after acetaminophen overdose. A cutoff of 1.5 separated viral hepatitis from the other two with 94% sensitivity and 84% specificity.¹⁸

ALT-to-LDH ratio = ALT ÷ LDH

Macro-LDH is a lab quirk. Sometimes an antibody binds LDH in the blood. The bound enzyme is cleared slowly, so it builds up and LDH stays high with no extra tissue damage behind it. Lab testing can sort this out when a high LDH persists and nothing explains it.²

Questions worth asking

• Was my sample hemolyzed, and should we repeat it with a clean draw?
• Could a hard workout, an injury or an illness in the past week explain it?
• What do my haptoglobin, bilirubin and reticulocyte count show?
• What do my CK, AST and ALT show next to it?
• Could any of my medicines or supplements be involved?
• If it stays high with no explanation, should the lab check for macro-LDH?

FAQ

What is a normal LDH level? It depends on your lab. Many adult ranges run from about 120 to 220–226 U/L: Oxford uses 125–220, and Labcorp uses 121–224 for men and 119–226 for women. Children run higher.³⁴

What are common causes of a high LDH? Common reasons include a hard workout or muscle injury, red cells bursting in the tube or in the body, and liver disease. The neighbors (CK, haptoglobin, bilirubin, ALT) show which one it is.¹⁸⁵

Can exercise raise LDH? Yes. After one hour of weightlifting, LDH peaked about 3 days later and took about 6 days to get back under the upper limit.⁵

Is LDH the same as lactate? No. Lactate is the molecule, and LDH is the enzyme that makes and uses it. They are separate blood tests that answer different questions.¹

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This guide is for education. The clinician who knows your history is the right person to interpret your result.

Footnotes

1. National Library of Medicine. Lactate Dehydrogenase (LDH) Test. MedlinePlus. Updated October 30, 2023. Which tissues hold the most LDH, common reasons for high and low results (exercise, aspirin, burst red cells, vitamins C and E), and which cancers it helps stage. MedlinePlus ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

2. Shipman AR, Bahrani S, Shipman KE. Investigative algorithms for disorders affecting plasma lactate dehydrogenase: a narrative review. J Lab Precis Med. 2024;9:15. Where LDH comes from, method differences, causes of high and low results, and macro-LDH. doi.org ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

3. Oxford University Hospitals NHS Foundation Trust. Lactate Dehydrogenase. Clinical Biochemistry test catalogue. Last reviewed April 23, 2025. Adult range 125–220 IU/L for both sexes. ouh.nhs.uk ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

4. Labcorp. Lactic Acid Dehydrogenase (LD), test 001115. Test catalog page, accessed September 23, 2026. A commercial lab's published reference ranges by age and sex, its grouping of causes by size of rise, sample-rejection rules, and the AST/ALT-to-LDH pattern in viral hepatitis. labcorp.com ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹

5. Pettersson J, Hindorf U, Persson P, et al. Muscular exercise can cause highly pathological liver function tests in healthy men. Br J Clin Pharmacol. 2008;65(2):253–259. After 1 hour of weightlifting: LDH, CK, AST and ALT time courses, with bilirubin, GGT and ALP unchanged. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹

6. Lippi G, Salvagno GL, Montagnana M, Brocco G, Guidi GC. Influence of hemolysis on routine clinical chemistry testing. Clin Chem Lab Med. 2006;44(3):311–316. Red cells burst in the tube raise LDH, AST, ALT, CK and potassium, even when the hemolysis is barely visible. PubMed ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

7. Indian National Association for the Study of the Liver and Federation of Obstetric and Gynaecological Societies of India. Position statement on management of liver diseases in pregnancy. J Clin Exp Hepatol. 2019;9(3):383–406. Reproduces the Tennessee and Mississippi HELLP classifications (LDH over 600 U/L) and HELLP symptoms. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵

8. Barcellini W, Fattizzo B. Clinical Applications of Hemolytic Markers in the Differential Diagnosis and Management of Hemolytic Anemia. Dis Markers. 2015;2015:635670. A hematology review of LDH, haptoglobin, bilirubin and reticulocytes in hemolysis. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

9. Giannini EG, Testa R, Savarino V. Liver enzyme alteration: a guide for clinicians. CMAJ. 2005;172(3):367–379. In acute viral hepatitis, LDH is raised in about half of patients and only slightly, while aminotransferases and bilirubin rise more. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

10. National Library of Medicine. Lactate dehydrogenase deficiency. MedlinePlus Genetics. Updated February 1, 2012. LDH-A and LDH-B deficiency, the four-subunit structure, and the muscle and heart forms. MedlinePlus Genetics ↩ ↩² ↩³ ↩⁴ ↩⁵

11. Kristiansen S, Friis-Hansen L, Antonio Juel Jensen C, Ingemann Hansen S. Verification study on the NORIP LDH reference intervals with a proposed new upper reference limit. Scand J Clin Lab Invest. 2018;78(5):421–427. A recalculated adult range of 127–240 U/L; the older Nordic limit of 205 U/L flagged 25.1% of results. doi.org ↩ ↩² ↩³ ↩⁴ ↩⁵

12. Weatherby D, Ferguson S. Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective. 2nd ed. Bear Mountain Publishing; 2004. ISBN 978-0976136712. The functional-medicine textbook the Libby app's marker catalog cites for its LDH optimal range of 140–180 U/L. ↩ ↩² ↩³

13. Optimal DX. Biomarkers of Liver and Gallbladder Function: LDH. Published November 10, 2022; updated April 29, 2024. Lists a "standard range" of 100–200 IU/L and an "ODX range" of 140–200 IU/L. A commercial source, listed as what the optimizer community uses. optimaldx.com ↩ ↩² ↩³

14. Petrelli F, Cabiddu M, Coinu A, et al. Prognostic role of lactate dehydrogenase in solid tumors: a systematic review and meta-analysis of 76 studies. Acta Oncol. 2015;54(7):961–970. 22,882 patients; hazard ratio for death 1.7 with a high LDH. PubMed ↩

15. Kato GJ, McGowan V, Machado RF, et al. Lactate dehydrogenase as a biomarker of hemolysis-associated nitric oxide resistance, priapism, leg ulceration, pulmonary hypertension, and death in patients with sickle cell disease. Blood. 2006;107(6):2279–2285. 213 adults; LDH tracked AST, bilirubin, reticulocytes and low haptoglobin, but not ALT or CK to the same degree. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵

16. Lippi G, Schena F, Salvagno GL, et al. Acute variation of biochemical markers of muscle damage following a 21-km, half-marathon run. Scand J Clin Lab Invest. 2008;68(7):667–672. LDH rose 1.3-fold and stayed raised 24 hours later. PubMed ↩ ↩²

17. Krishnamurthy K, Medina AM, Howard L. The Utility of Elevated Serum Lactate Dehydrogenase in Current Clinical Practice. Lab Med. 2021;52(2):e17–e22. One year of LDH tests in a 726-bed hospital. PubMed ↩

18. Cassidy WM, Reynolds TB. Serum lactic dehydrogenase in the differential diagnosis of acute hepatocellular injury. J Clin Gastroenterol. 1994;19(2):118–121. The ALT-to-LDH ratio in viral hepatitis, shock liver and acetaminophen injury. PubMed ↩ ↩² ↩³ ↩⁴

19. Liu S, Li J, Ning L, Wu D, Wei D. Assessing the influence of true hemolysis occurring in patient samples on emergency clinical biochemistry tests results using the VITROS 5600 Integrated system. Biomed Rep. 2021;15(5):91. 92 paired hemolyzed and clean samples: hemolysis raised LDH, AST and CK, while the shift in bilirubin and ALT depended on the lab's method. PMC ↩ ↩²

20. National Library of Medicine. Lactate Dehydrogenase (LDH) Isoenzymes Test. MedlinePlus. Updated October 30, 2023. Where LDH-1 to LDH-5 are found, what isoenzyme patterns suggest, and troponin's role for heart attacks. MedlinePlus ↩ ↩² ↩³ ↩⁴

21. Carobene A, Røraas T, Sølvik UØ, et al. Biological Variation Estimates Obtained from 91 Healthy Study Participants for 9 Enzymes in Serum. Clin Chem. 2017;63(6):1141–1150. The European Biological Variation Study: LDH varied 5.2% within a person and 12.6% between people. PubMed ↩