High LDH Blood Test: What Does It Mean, and Is It the Same as Lactate?

A high LDH blood test means there is more lactate dehydrogenase in the blood than the lab's reference range. LDH is released when cells are damaged, so a raised level is a sign that some tissue may be injured. It does not show which tissue, how it was damaged or whether treatment is needed.

MedlinePlus notes that LDH is in nearly all body tissues, with the largest amounts in muscles, the liver, the kidneys and red blood cells. Because so many tissues contain it, LDH is described as a non-specific marker. It is usually read alongside symptoms and other test results rather than on its own.

This guide is for adults looking at an LDH result that has already been reported. It cannot explain an individual result or replace a clinician's assessment.

An LDH number alone does not tell you how urgent things are. How you feel matters more. The NHS advises calling emergency services or going to an emergency department if an adult has signs that could be sepsis, such as:

• very fast breathing;
• confusion, slurred speech or not making sense;
• blue, pale or blotchy skin, lips or tongue;
• a rash that does not fade when pressed;
• a very high or very low temperature, or feeling hot or cold to the touch, or shivering.
• Also get emergency help for chest pain, severe breathlessness or fainting, and urgent advice for new yellowing of the skin or eyes. Do not wait for a repeat blood test.

No. The names sound alike, which causes confusion. LDH (lactate dehydrogenase) is an enzyme that helps cells make energy. Lactate, often called lactic acid, is a substance made mainly by muscles and red blood cells during energy production and cleared by the liver and kidneys.

MedlinePlus describes the lactate test as a way to look for problems with oxygen delivery or energy use, for example in shock, severe infection or sepsis, heart failure or serious lung disease. Lactate is a test linked with how well the body is coping with oxygen supply, which is why it matters when someone is acutely unwell. A high LDH, by contrast, is a broader sign of possible tissue damage that may be acute or long-standing.

Check the exact test name on your report. If it says LDH or LD, it is the enzyme. If it says lactate or lactic acid, it is the other test, and the questions to ask are different.

Yes. Red blood cells contain a lot of LDH. If they break open while blood is being taken, transported or processed, LDH leaks into the sample and the result can read falsely high. This is called haemolysis (hemolysis). Both MedlinePlus and Cleveland Clinic list it as a cause of a raised result.

Some labs note on the report when a sample was haemolysed. Sample problems can affect other results too; potassium is a well-known example, covered in our separate guide. If your report mentions haemolysis, ask whether the result should be repeated before drawing conclusions.

Haemolysis in the tube is different from haemolysis in the body, where red blood cells break down inside the bloodstream. That is one of the real causes of high LDH, so the clinician will think about which one fits.

MedlinePlus and Cleveland Clinic list many possible causes. This list is not a checklist to work through on your own; it shows how wide the range is.

• Blood conditions, including some types of anaemia where red cells break down.
• Liver, kidney, lung, heart or pancreas conditions, including heart attack and pancreatitis.
• Muscle injury, muscular dystrophy or a bone fracture.
• Infections such as meningitis, encephalitis, glandular fever (mono), HIV or other severe infections.
• Some cancers, including lymphoma, leukaemia, multiple myeloma, melanoma and testicular cancer.
• Non-disease factors: strenuous exercise and some medicines, such as aspirin, anaesthetics, narcotics and procainamide.

Not on its own. The National Cancer Institute lists LDH as a tumour marker for some cancers, including germ cell tumours, lymphoma, leukaemia, melanoma and neuroblastoma. It says LDH is used to help assess stage, outlook and response to treatment. It is not listed as a test to diagnose cancer.

Most of the causes above are not cancer. If you are already being treated for cancer, your team may track LDH over time, and the trend matters more than a single value. Ask them what change they are watching for.

Ranges differ between laboratories and methods, so always use the range printed on your report. As a guide, Cleveland Clinic gives typical adult ranges of about 135 to 225 units per litre (U/L) for males and 135 to 214 U/L for females, and notes that children usually have higher normal levels.

Next steps depend on the whole picture. A clinician may look at your symptoms, medicines, a full blood count, liver and kidney tests or muscle tests. The LDH may be repeated, especially if haemolysis or recent hard exercise is possible. MedlinePlus notes that an LDH isoenzyme test can help show which type of tissue the LDH is coming from.

Do not stop or change a prescribed medicine because of an LDH result without talking to the prescriber.

Take the full report, including the date, units and reference range, and a list of your medicines and recent exercise.

• Was this LDH or lactate, and why was it ordered?
• Did the lab flag the sample as haemolysed, and should it be repeated?
• Do my other results, such as blood count, liver, kidney or muscle tests, point to a source?
• Could recent exercise or any of my medicines have affected it?
• Is an isoenzyme test or other follow-up needed, and when will I hear about it?
• Which new symptoms should make me seek care before the next test?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a raised LDH were followed up, for example whether a repeat test was done or what other tests were added, can help you prepare clearer questions. Every case is different, and similar cases cannot explain your own result. Your clinician remains the person to interpret it.