- 01LDH says that cells are breaking down; the partner marker says where
LDH is in almost every tissue, so a high result means cells are breaking down somewhere. The marker that is abnormal alongside it names the place: low haptoglobin means red cells, high ALT means the liver, very high CK means muscle, high troponin means the heart.
LDH (lactate dehydrogenase) is an enzyme that helps cells turn sugar into energy. Nearly every tissue has it, with the most in the heart, liver, skeletal muscle, kidneys, red blood cells and lungs 1. When cells break open, their LDH spills into the blood. So a high LDH result says that some tissue is releasing it, but nothing on the LDH line says which one. The other results on the same report usually name the tissue.
Start with the marker itself
How high counts as high LDH
An adult reference interval of about 140 to 280 U/L (units per liter) is commonly cited 1, but the number depends on the lab's method. Many labs print an upper limit of about 220 to 250 U/L, while some older methods print ranges as high as 313 to 618 U/L. A result of 400 U/L is therefore clearly high at one lab and normal at another. The fair way to compare is to divide your result by your own lab's upper limit. Read this way, a result of 330 against a limit of 220 and a result of 420 against a limit of 280 are both 1.5 times the limit. More on why ranges differ is in <a href="/learn/reference-ranges-explained">reference ranges explained</a>.
Where an example LDH of 340 U/L fallsU/L
| Band | Multiple of upper limit | On a 140 to 280 scale | On a 125 to 220 scale | What it usually points to |
|---|---|---|---|---|
| Within range | Up to 1x | Up to 280 | Up to 220 | Usually no sign of excess cell breakdown |
| Mildly raised | 1 to 1.5x | 281 to 420 | 221 to 330 | Red cells burst in the tube (sample hemolysis), recent hard exercise, mild liver or muscle strain, a recent infection |
| Clearly raised | 1.5 to 3x | 421 to 840 | 331 to 660 | Active liver or muscle injury, red cell breakdown, significant infection; needs a work-up with your doctor |
| Very high | Over 3x | Over 840 | Over 660 | Major red cell breakdown, severe B12 deficiency, widespread tissue injury, some blood cancers; contact your doctor within a day or two, the same day if you have symptoms |
On a 140 to 280 range, the multiples work out like this. An LDH of 300 is 1.07 times the limit, a borderline result that very often comes back normal on a clean repeat. An LDH of 400 is 1.4 times the limit, still in the mild band, and worth repeating and reading next to the liver and muscle markers. An LDH of 1,000 is more than 3.5 times the limit: even if you feel well, contact your doctor within a day or two rather than waiting for a routine appointment.
Rule out a false high first
Red blood cells hold far more LDH than the plasma around them. When red cells burst in the tube (in-vitro hemolysis), they release that LDH and the result climbs even though nothing is happening in your body. In a study of routine chemistry tests, Lippi and colleagues found that even slight hemolysis measurably raises LDH 2. A hard draw, a thin needle, shaking the tube, or a long wait before the sample is spun down can all cause it.
- Read the lab comments. A note such as 'hemolyzed', 'H index' or 'slight hemolysis' means the LDH figure cannot be trusted.
- Check whether <a href="/biomarkers/potassium-serum">potassium</a> on the same report is also high. Bursting red cells release potassium too, and both rising together points to the sample.
- Think back over the 72 hours before the draw: hard training, a long run, heavy lifting, an injury, a fever, a new medicine.
- Before a repeat, skip hard exercise for two to three days and ask for the sample to be processed promptly.
If LDH stays slightly high on every repeat while everything else is normal, a rare harmless cause is macro-LDH. In macro-LDH, the enzyme binds to an antibody, and the larger complex stays in the blood longer. A lab can identify it with a special test, and it usually needs no treatment.
Common causes of high LDH, from everyday to serious
The table runs roughly from the most common causes in people who feel well to the less common and serious ones. The second column shows how high each cause usually pushes LDH, which helps put a single number in proportion. The next section shows which partner result points to each one.
| Cause | How high LDH usually goes |
|---|---|
| Sample hemolysis | Mild to moderate; normal on a clean repeat |
| Hard or unfamiliar exercise, such as a marathon or heavy lifting 10 | Mild, for one to several days |
| Liver strain (fatty liver, alcohol, medicines, hepatitis) | Mild to moderate |
| Muscle injury (trauma, statin muscle side effects, rhabdomyolysis) | Mild to very high |
| Hemolytic anemia (red cells destroyed inside the body) | Moderate to very high |
| B12 or folate deficiency | Can be very high, sometimes into the thousands |
| Infections (pneumonia, severe viral illness including COVID-19 12) | Moderate to high |
| Blood clot in the lung, heart attack, kidney infarct | Moderate |
| Pregnancy complications (HELLP) | 600 U/L or more |
| Cancers (lymphoma, leukemia, germ cell tumors, melanoma, widespread disease) | Mild to very high |
Severe B12 or folate deficiency can push LDH very high because the bone marrow makes red cells that die before they are released; the <a href="/conditions/b12-deficiency">B12 deficiency</a> page covers that pattern. Statins can cause muscle injury in a small number of people, and that shows up as high CK and LDH. If you take a statin and have muscle pain or weakness, tell your prescriber rather than stopping or changing it yourself; muscle pain with dark urine needs same-day care. The <a href="/compounds/statins">statins and your labs</a> page explains how to read the results. Fatty liver, one of the most common liver causes, has its own page at <a href="/conditions/fatty-liver">fatty liver</a>.
Where the LDH is coming from: read it with its partners
A high LDH is a general signal of cell breakdown, and the partner results narrow it down to a tissue. Each tissue releases its own markers along with LDH: the liver releases ALT, muscle releases CK, and the heart releases troponin. Red cells destroyed inside the body use up haptoglobin, a protein that mops up the hemoglobin they release. A high LDH with a low haptoglobin is about 90% specific for red cell destruction 3. Indirect bilirubin (the form made from broken-down hemoglobin before the liver processes it) and reticulocytes (young red cells, a sign the marrow is replacing lost ones) usually rise as well.
| LDH plus... | Likely source | Usually checked next |
|---|---|---|
| Low haptoglobin, high indirect bilirubin, high reticulocytes | Red cells breaking down inside the body | Blood smear, Coombs test (checks whether antibodies are attacking red cells), CBC |
| High ALT and AST | Liver | Liver panel, ultrasound, hepatitis tests, alcohol and medicine review |
| Very high CK, with high AST, sometimes dark urine | Skeletal muscle | Repeat CK after rest, kidney function, urine for blood pigment |
| High troponin | Heart | Same-day ECG and repeat troponin |
| Low platelets and anemia, with fragmented red cells on the smear | Tiny clots in small blood vessels that shred red cells (thrombotic microangiopathy, such as TTP); urgent 13 | Same-day hospital assessment |
| Large red cells (high MCV) and low hemoglobin | Faulty red cell production (B12 or folate) | B12, folate, methylmalonic acid |
| High CRP, abnormal white cell count | Infection or inflammation | Depends on symptoms |
| Everything else normal | Sample issue, recent exercise or macro-LDH | Clean repeat in 1 to 2 weeks |
The partners that show where LDH is coming from
The liver enzymes have their own guide in <a href="/learn/liver-enzymes-explained">liver enzymes explained</a>, and the red cell side of the panel, including <a href="/biomarkers/mcv">MCV</a>, is covered in <a href="/learn/cbc-explained">the CBC explained</a>. A low hemoglobin next to a high LDH is the place to start on <a href="/conditions/anemia">anemia</a>.
The five LDH isoenzymes
LDH comes in five forms (isoenzymes), and each tissue has a different mix 1:
| Isoenzyme | Main tissues |
|---|---|
| LDH-1 and LDH-2 | Heart muscle, red blood cells, kidney |
| LDH-3 | Lungs and lymphoid tissue |
| LDH-4 and LDH-5 | Liver and skeletal muscle |
An isoenzyme breakdown was once the standard way to locate the source. Doctors rarely order it now, because ALT, CK, troponin and haptoglobin answer the same question faster and more precisely.
Does high LDH mean cancer?
No, a high LDH on its own does not mean cancer, and LDH is not a screening test for cancer. Exercise, the liver and red cells explain far more high results than tumors do. LDH matters in oncology after a cancer has been diagnosed, as one of the numbers used to stage it and estimate how aggressive it is. In aggressive non-Hodgkin lymphoma, for example, an LDH above the upper limit is one of the five adverse factors in the International Prognostic Index 5.
| Cancer | How LDH is used |
|---|---|
| Aggressive non-Hodgkin lymphoma | One of five factors in the International Prognostic Index 5 |
| Multiple myeloma | Part of the Revised International Staging System (R-ISS) 7 |
| Stage IV melanoma | Staging by the AJCC (American Joint Committee on Cancer) adds an LDH flag, because a high LDH carries a worse outlook 8 |
| Testicular germ cell tumors | Used with AFP and hCG (two tumor proteins) for serum staging: S1 under 1.5x the upper limit, S2 1.5 to 10x, S3 over 10x |
Across 76 studies in solid tumors, a high LDH before treatment was linked with worse overall survival, with a hazard ratio of about 1.48 9. A normal LDH does not rule cancer out either, because many early cancers leave LDH unchanged. If you are worried about a specific cancer, the useful steps are symptoms, an examination and tests built for that cancer. The <a href="/learn/tumor-markers-explained">tumor markers explainer</a> covers how markers like LDH, AFP and hCG are meant to be used.
LDH and the heart
LDH was once a standard test for heart attacks, because it rises a day or so after the event and stays up for over a week. Today a heart attack is diagnosed by a rise or fall in troponin, a protein released by damaged heart muscle, together with symptoms, ECG changes or imaging evidence 4. A high LDH therefore says little about the heart unless troponin is also high. If you have chest pain, call emergency services rather than reading lab results. For a raised troponin, see <a href="/biomarkers/troponin-i-hs/high">high troponin</a> and <a href="/learn/cardiac-markers-explained">cardiac markers explained</a>.
High LDH in pregnancy and in children
LDH can rise a little in a healthy pregnancy. In the second half of pregnancy, a high LDH is a warning sign for HELLP syndrome, a severe form of preeclampsia. ACOG's diagnostic pattern is an LDH of 600 U/L or more, AST and ALT more than twice the upper limit, and a platelet count below 100,000 per microliter 6. A pregnant person with a high LDH who also has a headache, vision changes, pain under the right ribs, nausea or swelling needs to be seen the same day, at labor and delivery or an emergency department.
Children, and newborns especially, normally have higher LDH than adults because they are growing fast 11. A child's result has to be read against an age-matched range, which most pediatric labs print on the report. An adult range will flag many healthy children as high.
When a high LDH needs urgent attention
Without any of those, a high LDH is not an emergency. A mild or moderate rise in someone who feels well still deserves follow-up: a repeat test and a look at the partner markers within a few weeks.
How to bring a high LDH down
Bringing LDH down means finding and treating whatever is releasing it. No supplement lowers LDH directly, and lowering the number without fixing the cause would only hide the signal. When the cause settles, LDH follows: within days after exercise, and after a liver or red cell problem as that problem resolves. More on the organ behind many mild rises is on the <a href="/topics/liver">liver hub</a>, and if tiredness is what led to the test, see <a href="/symptoms/fatigue">fatigue</a>.
What to do next with a high LDH
These are the steps a clinician usually works through. Take them to whoever ordered the test, who can read the result alongside your history and medicines.
- 1Work out the multipleDivide your LDH by your lab's upper limit. Under 1.5 times the limit is mild; over 3 times means contacting your doctor within a day or two.
- 2Read the rest of the panelLook at AST, ALT, CK, bilirubin, potassium and the CBC (hemoglobin, MCV, platelets) on the same report. The partner that is also abnormal usually names the source.
- 3Recall the 72 hours before the drawNote any hard training, alcohol, illness, injury or new medicine.
- 4Take it to your clinicianBook a routine appointment and bring the full report and your 72-hour notes. Ask whether these add-ons fit: haptoglobin, reticulocytes and a blood smear if red cells are the suspect; CK if muscle; troponin if the heart; B12 and folate if the red cells are large.
- 5Repeat with a clean drawRepeat in 1 to 2 weeks, after 2 to 3 days without hard exercise. The <a href="/learn/how-to-prepare-for-a-blood-test">blood test preparation guide</a> covers the rest.
- 6Track the trendA steady 300 across three tests means something different from 190 jumping to 350. <a href="/learn/trends-beat-single-readings">Trends beat single readings</a> explains why.
Citations
- Farhana A, Lappin SL. Biochemistry, Lactate Dehydrogenase. StatPearls (2023)
- Lippi G et al. Influence of hemolysis on routine clinical chemistry testing. Clin Chem Lab Med (2006)
- Barcellini W, Fattizzo B. Clinical applications of hemolytic markers in the differential diagnosis and management of hemolytic anemia. Dis Markers (2015)
- Thygesen K et al. Fourth Universal Definition of Myocardial Infarction. Circulation (2018)
- Shipp MA et al. A predictive model for aggressive non-Hodgkin's lymphoma. N Engl J Med (1993)
- ACOG Practice Bulletin No. 222: Gestational Hypertension and Preeclampsia. Obstet Gynecol (2020)
- Palumbo A et al. Revised International Staging System for Multiple Myeloma. J Clin Oncol (2015)
- Gershenwald JE et al. Melanoma staging: evidence-based changes in the American Joint Committee on Cancer eighth edition cancer staging manual. CA Cancer J Clin (2017)
- Petrelli F et al. Prognostic role of lactate dehydrogenase in solid tumors: a systematic review and meta-analysis of 76 studies. Acta Oncol (2015)
- Brancaccio P, Lippi G, Maffulli N. Biochemical markers of muscular damage. Clin Chem Lab Med (2010)
- Colantonio DA et al. Closing the gaps in pediatric laboratory reference intervals: a CALIPER database of 40 biochemical markers. Clin Chem (2012)
- Henry BM et al. Lactate dehydrogenase levels predict coronavirus disease 2019 (COVID-19) severity and mortality: a pooled analysis. Am J Emerg Med (2020)
- George JN, Nester CM. Syndromes of thrombotic microangiopathy. N Engl J Med (2014)
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.
