Medical & affiliate disclosure: CTX Stat provides educational laboratory information and is not a substitute for professional medical advice, diagnosis, or treatment. CTX Stat may receive compensation from some outbound provider links when an affiliate program is active; provider comparisons and rankings are based on consumer fit, effective cost, access, policies, and reputation—not commission.
Quick take
The LDH blood test measures lactate dehydrogenase, an enzyme found in almost all body tissues. LDH helps cells make energy, and a small amount normally circulates in the blood. When cells are injured, inflamed, destroyed, or stressed, LDH can leak into the bloodstream and rise above the laboratory’s reference range. The test is useful as a broad signal of tissue damage, but it is not specific: an abnormal result does not tell you by itself which organ is involved or what diagnosis you have.
- What it measures: the amount of lactate dehydrogenase enzyme in blood, usually reported in units per liter (U/L or IU/L).
- Common reasons it is ordered: evaluation of possible tissue injury, liver or muscle problems, hemolysis, severe infection or inflammation, certain cancers, and monitoring of some known conditions.
- Preparation: no special preparation is usually needed for an LDH blood test, but follow any instructions for other tests drawn at the same time.
- Key limitation: LDH can be elevated by many conditions and by sample hemolysis, meaning red blood cells broke open during or after collection.
- Best next step: interpret LDH alongside symptoms, exam findings, and companion tests such as CBC, liver enzymes, creatine kinase, bilirubin, haptoglobin, kidney tests, inflammatory markers, or tumor markers when appropriate.
On this page
What is LDH?
LDH stands for lactate dehydrogenase, sometimes called lactic acid dehydrogenase. It is an enzyme involved in the chemical reactions cells use to produce energy. According to MedlinePlus, LDH is present in many tissues, with relatively large amounts in muscles, liver, kidneys, and red blood cells. Because LDH is so widely distributed, it can rise whenever cells in many different parts of the body are damaged.
That broad distribution is both the strength and weakness of the test. LDH can alert a clinician that something is causing tissue injury, but it usually cannot identify the exact source. For example, LDH may rise with liver inflammation, muscle injury, hemolytic anemia, certain infections, lung injury, some cancers, or even a difficult blood draw that damages red blood cells in the tube. For this reason, an LDH blood test is most useful when it is ordered with a clinical question in mind and interpreted with other test results.
LDH can also be measured in certain body fluids, such as pleural fluid from around the lungs, peritoneal fluid from the abdomen, or cerebrospinal fluid around the brain and spinal cord. This article focuses mainly on the blood test, but the same enzyme can be used in fluid analysis when clinicians are evaluating fluid buildup, infection, inflammation, or other conditions.
Why clinicians order an LDH blood test
An LDH test is most often used as a general marker of cell or tissue damage. MedlinePlus notes that LDH testing may be used in many settings, including conditions affecting the blood, liver, lungs, kidneys, heart, pancreas, brain, spinal cord, muscles, severe infections, and certain cancers. It may also be used to monitor some conditions over time or evaluate whether treatment is working.
Common situations where LDH may be ordered include:
- Unexplained symptoms with concern for tissue injury: fatigue, weakness, fever, pain, shortness of breath, jaundice, dark urine, or abnormal imaging may lead a clinician to order LDH with other tests.
- Evaluation of anemia or hemolysis: when red blood cells are breaking down, LDH may rise along with indirect bilirubin and reticulocytes, while haptoglobin may fall.
- Liver or muscle evaluation: LDH may be ordered with AST, ALT, alkaline phosphatase, bilirubin, creatine kinase, and other chemistry tests.
- Monitoring known disease: in some cancers or inflammatory conditions, trends in LDH may help clinicians understand disease activity, severity, or treatment response.
- Assessment of body fluids: LDH in pleural or other fluids may help classify the nature of fluid accumulation when interpreted with protein, glucose, cell counts, cultures, and other measurements.
LDH is not usually a stand-alone screening test for healthy people. A normal LDH does not rule out disease, and an elevated LDH does not automatically mean a serious diagnosis. The value comes from the pattern: how high it is, whether it is rising or falling, what other labs show, and what is happening clinically.
Preparation and what happens during the test
For a standard LDH blood test, no special preparation is usually required. MedlinePlus states that people generally do not need to do anything special before an LDH blood test. If LDH is being drawn as part of a larger panel, however, instructions may depend on the other tests. For example, some metabolic, lipid, or glucose tests may involve fasting, while LDH by itself typically does not.
Before the draw, tell the ordering clinician or collection site about medications and supplements you take, especially if you were specifically instructed to review them. Do not stop prescribed medicine just to change an LDH result unless your clinician tells you to. MedlinePlus notes that intense exercise and certain medicines, including aspirin, may affect LDH levels in some cases, and high-dose vitamins C or E have been associated with lower LDH results.
The blood draw is straightforward. A healthcare professional cleans the skin, places a needle into a vein, collects a small amount of blood in a tube, and removes the needle. The process usually takes only a few minutes. Mild stinging, temporary soreness, or bruising can happen and typically resolves quickly.
Because red blood cells contain LDH, careful specimen handling matters. If red blood cells break open during collection, transport, or processing, LDH can be falsely elevated. Laboratory sources such as the CDC NHANES laboratory procedure manual emphasize that hemolysis can make LDH results unreliable by releasing LDH from damaged red cells. If a result is unexpectedly high and the specimen was hemolyzed, a repeat draw may be needed.
How to read LDH results
LDH results are usually reported as a number with a reference range. A typical adult reference interval may be around 120–225 U/L, but ranges vary by laboratory, age, sex, specimen type, and analytic method. For example, MedlinePlus Medical Encyclopedia lists a general normal range of 125 to 220 IU/L, while Labcorp’s LD test information provides age- and sex-specific adult reference ranges that differ slightly. Always compare your result with the range printed on your own report.
| Result pattern | What it may suggest | How it is usually interpreted |
|---|---|---|
| Within the reference range | No LDH elevation detected at the time of testing | Does not rule out all disease; interpretation depends on symptoms and other tests |
| Mildly elevated | Possible minor tissue injury, recent strenuous exercise, sample hemolysis, or early/low-grade disease activity | Often repeated or interpreted with CBC, liver enzymes, muscle enzymes, and clinical context |
| Moderately to markedly elevated | More significant tissue injury, hemolysis, liver disease, muscle injury, severe infection/inflammation, some cancers, or other causes | Usually prompts focused evaluation based on symptoms, exam, and companion tests |
| Low LDH | Usually not clinically important | May be associated with high-dose vitamin C or E or rare inherited LDH deficiency, but low values are uncommon |
It is tempting to search for a single “dangerous LDH level,” but there is no universal cutoff that applies to everyone. A value slightly above range may be important in one situation and unimportant in another. A higher value may require urgent attention if it occurs with chest pain, severe anemia, jaundice, neurologic symptoms, breathing problems, high fever, low blood pressure, or other concerning findings. The same number may be handled differently if it occurs after strenuous exercise or in a visibly hemolyzed sample.
What high LDH may mean
A high LDH means more LDH than expected is present in the blood sample. In general, this suggests cells have released LDH, but the test does not identify the location. Below are common categories clinicians consider.
Blood cell breakdown and anemia
LDH is abundant in red blood cells. When red cells are destroyed inside the body, LDH can rise. This may occur in hemolytic anemia, transfusion reactions, some autoimmune conditions, mechanical destruction of red cells, severe infections, or inherited red-cell disorders. In this setting, clinicians usually look at a CBC, reticulocyte count, bilirubin, haptoglobin, peripheral smear, and sometimes a direct antiglobulin test. A high LDH plus low haptoglobin and high indirect bilirubin can support hemolysis, but the full pattern matters.
Liver, muscle, and organ injury
LDH may rise with liver inflammation or injury, muscle trauma, muscular dystrophy, pancreatitis, kidney injury, lung disease, and other tissue-damaging conditions. MedlinePlus lists liver disease, muscle injury, pancreatitis, stroke, tissue death, and low blood pressure among possible causes of higher-than-normal LDH. When liver disease is suspected, LDH is usually less specific than AST, ALT, alkaline phosphatase, bilirubin, albumin, and prothrombin time. When muscle injury is suspected, creatine kinase is often more directly informative.
Infection, inflammation, and severe illness
Severe infections and inflammatory states can damage cells or reduce tissue oxygen supply, causing LDH to rise. LDH may be one part of a broader workup that includes a CBC, metabolic panel, inflammatory markers, cultures, imaging, and clinical assessment. The LDH result alone does not show whether an infection is bacterial, viral, localized, or systemic.
Cancer monitoring and tumor-marker context
LDH can be used in some cancer contexts, but it is not a general cancer screening test. The American Cancer Society explains that LDH may be elevated in testicular cancer and can be followed with AFP and hCG before, during, and after treatment. The same source cautions that LDH can also rise with many noncancerous conditions. For lymphoma, the American Cancer Society notes that LDH may be checked after lymphoma is diagnosed and is often increased in people with lymphomas.
In cancer care, LDH is interpreted by oncology teams in a specific disease framework. It may contribute to staging, risk assessment, or treatment monitoring in selected cancers, but it does not diagnose cancer by itself. If LDH was ordered as part of a tumor-marker panel, ask which condition is being monitored, which companion markers matter, and what degree of change would be clinically meaningful.
What low LDH may mean
Low LDH values are uncommon and usually not a health concern. MedlinePlus notes that lower-than-normal LDH levels are usually not considered a medical problem and may be related to large amounts of vitamin C or vitamin E. Rare inherited LDH deficiency can cause low levels, but this is not a common explanation for routine test results.
If your LDH is low and every other result is normal, it is often simply documented without further action. If the low result appears inconsistent with your clinical picture or supplement use, your clinician may decide whether repeat testing is worthwhile.
Limitations and false results
The most important thing to know about LDH is that it is sensitive to many kinds of cell injury but not specific to one disease. A high result can be meaningful, but it is rarely diagnostic by itself. Several limitations can affect interpretation:
- Hemolysis can falsely elevate LDH. If red blood cells break open in the tube, LDH from the cells enters the serum or plasma. Labcorp’s test information states that hemolysis elevates LDH results, and the CDC NHANES procedure manual says hemolysis is unacceptable for LDH measurement because it can falsely raise results.
- Exercise can raise LDH. Strenuous activity may cause muscle-related enzyme changes, especially when paired with soreness or elevated creatine kinase.
- Medications and supplements may influence results. Aspirin is listed by MedlinePlus as a possible contributor to high LDH in some situations, while large amounts of vitamins C or E may be linked with low LDH.
- Reference ranges vary. Different laboratories use different instruments, methods, specimen requirements, and population-based intervals. Use the range on your own report rather than comparing your number with a random online range.
- Trends may matter more than one value. A falling LDH after treatment or recovery may be reassuring in the right context, while a rising LDH may prompt further evaluation.
LDH versus related tests
LDH is often ordered with other tests because it needs context. The table below shows how LDH differs from several common companion tests.
| Test | What it helps evaluate | How it relates to LDH |
|---|---|---|
| CBC | Red cells, white cells, hemoglobin, platelets | Helps identify anemia, infection patterns, or blood-count abnormalities that may explain LDH changes |
| AST and ALT | Liver-cell injury; AST can also rise with muscle injury | Helps determine whether LDH elevation may be liver-related |
| Bilirubin and haptoglobin | Red-cell breakdown and liver/bile processing | Often used with LDH when hemolysis is suspected |
| Creatine kinase | Skeletal or cardiac muscle injury | More specific than LDH for many muscle-injury questions |
| AFP and hCG | Selected tumor-marker evaluation, especially testicular cancer | May be followed with LDH in specific oncology contexts |
| LDH isoenzymes | Distribution of LDH subtypes | Historically used to help localize tissue source; now less commonly used in many settings |
What to do after an abnormal LDH result
If your LDH is abnormal, start with the basics before assuming the worst. Review the reference range, specimen comments, and whether the report mentions hemolysis. Then look at the tests drawn at the same time. A mildly high LDH with a hemolyzed specimen may need a repeat draw. A high LDH with abnormal liver enzymes suggests a different path than a high LDH with anemia and low haptoglobin.
Useful questions to ask your clinician include:
- Was my sample hemolyzed or otherwise flagged by the lab?
- How far outside the reference range is the result?
- Which organ system or condition were you evaluating when you ordered LDH?
- Do my CBC, liver enzymes, bilirubin, kidney tests, or muscle enzymes point to a likely source?
- Should LDH be repeated, and if so, when?
- Are there symptoms that should prompt urgent care rather than waiting for follow-up?
Seek prompt medical attention if an abnormal LDH occurs with severe chest pain, trouble breathing, fainting, stroke-like symptoms, severe weakness, yellowing of the skin or eyes, dark urine with anemia symptoms, high fever with confusion, or rapidly worsening symptoms. LDH is only one data point; symptoms and clinical severity matter most.
Cost and access considerations
The LDH blood test is a common chemistry test and is often billed under CPT code 83615. Your out-of-pocket cost depends on how the test is ordered, whether it is part of a panel, your insurance plan, deductible status, collection site, and whether any ordering or draw fees apply. In a clinician-ordered setting, insurance may cover LDH when it is medically necessary, but copays, deductibles, or coinsurance may still apply.
If you are paying cash or using a direct-to-consumer lab marketplace, compare the effective total cost, not just the advertised test price. The final cost may include the LDH test itself, a clinician order or review fee, a specimen collection fee, taxes where applicable, and any required service charges. Also confirm whether the lab location is convenient, whether your state allows the ordering workflow offered, how results are delivered, and whether follow-up with a healthcare professional is included or separate.
Because LDH is nonspecific, ordering it without a clear reason may create confusion or unnecessary follow-up. If you are considering self-ordering, think about what question the result is supposed to answer and whether related tests are needed for interpretation. For many concerns, a clinician-directed panel is more useful than LDH alone.
FAQs about the LDH blood test
What does an LDH blood test show?
An LDH blood test shows the level of lactate dehydrogenase enzyme in your blood. Higher-than-normal LDH often means some type of tissue or cell damage has occurred, but it does not identify the exact cause or location by itself.
Is high LDH always serious?
No. High LDH can occur for many reasons, including sample hemolysis, strenuous exercise, muscle injury, liver inflammation, hemolysis, infection, severe illness, and certain cancers. The seriousness depends on the level, symptoms, specimen quality, and other test results.
Can LDH diagnose cancer?
LDH does not diagnose cancer by itself and is not a general cancer screening test. It may be used as a tumor marker or monitoring test in specific cancers, such as testicular cancer or lymphoma, when interpreted with disease-specific markers, imaging, biopsy results, and oncology guidance.
Do I need to fast before an LDH test?
Usually, no. LDH by itself typically does not require fasting. If other tests are ordered at the same time, follow the instructions you were given for the entire blood draw.
What is a normal LDH level?
Normal ranges vary by lab. MedlinePlus lists a general range of 125 to 220 IU/L, and major laboratories may publish slightly different age- and sex-specific ranges. Use the reference interval printed on your own lab report.
Why would my doctor repeat LDH?
LDH may be repeated if the first sample was hemolyzed, if the result was unexpected, or if your clinician is monitoring a condition over time. A trend can be more useful than a single number.
What can falsely raise LDH?
Hemolysis is a major cause of falsely high LDH because red blood cells contain LDH. Strenuous exercise and some medications may also contribute to higher values in certain situations.
What other tests are usually checked with LDH?
Depending on the reason for testing, LDH may be interpreted with a CBC, reticulocyte count, bilirubin, haptoglobin, liver enzymes, creatine kinase, kidney function tests, inflammatory markers, or tumor markers such as AFP and hCG.
Sources
- MedlinePlus: Lactate Dehydrogenase (LDH) Test
- MedlinePlus Medical Encyclopedia: Lactate dehydrogenase test
- Labcorp: Lactic Acid Dehydrogenase (LD)
- CDC NHANES Laboratory Procedure Manual: Lactate Dehydrogenase
- American Cancer Society: Tests for Testicular Cancer
- American Cancer Society: Tests for Non-Hodgkin Lymphoma
