High LDH on a Blood Test: What It Means
Medically Reviewed by Dr. Pedro Yelamo Vera, MD
Licensed Physician No. 484814280 · Official Medical College of Bizkaia (Spain)Last reviewed: 31 October 2026
High LDH on a blood test is often harmless: exercise or a damaged sample. Normal ranges in the US, UK and Spain, real causes and what happens next.
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Dr. Pedro Yelamo Vera is an independent, bilingual GP licensed in Spain. Book a 15-minute video consultation in English or Spanish for €50, with a private electronic prescription issued under Spanish law when clinically appropriate.
A high LDH result means some cells have released more of this enzyme into your blood than usual. LDH is found in almost every tissue, so it does not point to one organ. A mild rise is often caused by hard exercise or a damaged sample. A doctor reads it with your other results and your symptoms.
- LDH (lactate dehydrogenase) is an enzyme in muscles, liver, kidneys, red blood cells and most other tissues.
- MedlinePlus gives a normal adult range of 125 to 220 IU/L. Each lab sets its own range, and children have higher ones.
- Common harmless causes: hard exercise, some medicines such as aspirin, and red cells breaking in the sample tube.
- Real causes include liver disease, muscle injury, glandular fever, red cell breakdown (haemolysis) and, less often, some cancers.
- LDH alone cannot show what is wrong or where. The next step is usually a repeat test and a look at other results.
Dr. Pedro Yelamo Vera is a GP licensed in Spain (Colegiado No. 484814280).
For a medical emergency, call 112 or go to the nearest local emergency department. Do not wait for a video consultation or an online reply.
What is LDH on a blood test?
LDH stands for lactate dehydrogenase. It is an enzyme that helps cells make energy. MedlinePlus explains that it is found in nearly all body tissues. The highest amounts are in muscles, liver, kidneys and red blood cells.
When cells are damaged, they release LDH into the blood. So a high result is a general sign of cell damage somewhere. It is not a test for one disease.
On a Spanish report, look for LDH or lactato deshidrogenasa. Some reports in Spanish write DHL. The unit is usually U/L or IU/L, which mean the same here. A star, an arrow or an "H" next to the value means it is above the lab range.
What is a normal LDH level?
There is no single normal range. It depends on the lab and the method it uses.
- US: MedlinePlus gives 125 to 220 IU/L for adults.
- UK: NHS labs set their own limits. North Bristol NHS Trust, for example, uses an upper limit of 250 U/L from age 10.
- Spain: each lab prints its own range next to your result. That is the one to use.
Children have higher limits. The same NHS lab allows up to 270 U/L between 1 and 10 years, and much more in newborns. So a child's value that looks high on an adult scale may be normal.
When you compare reports from different countries, compare each value with its own range. Do not compare raw numbers.
Can a high LDH be a false result?
Yes, and this is common. MedlinePlus lists three things that can raise LDH without any disease:
- Hard exercise in the days before the test. Muscles release LDH after heavy training.
- Some medicines, including aspirin.
- A damaged sample. If red cells break while blood is taken or handled, they spill LDH into the tube. Labs call this a haemolysed sample (muestra hemolizada).
The North Bristol lab adds that a delay before the sample reaches the lab can also affect the result. If your report says the sample was haemolysed, the LDH value is not reliable. A repeat test is usually the answer.
What conditions cause high LDH?
MedlinePlus lists many possible causes. Some are mild and short-lived. Others are serious. The list includes:
- Liver disease, such as hepatitis.
- Muscle injury or muscle disease, such as muscular dystrophy.
- Haemolytic anaemia, where red cells break down early in the body.
- Infectious mononucleosis, called glandular fever in the UK and mononucleosis in Spain.
- Pancreatitis, an inflamed pancreas.
- A heart attack, a stroke or poor blood flow to a tissue.
- Some blood cancers, such as leukaemia or lymphoma, and some other cancers.
Most of these cause clear symptoms. A slightly high LDH in someone who feels well is far more likely to be exercise, a medicine or the sample.
Got a high LDH result and not sure what it means?
You can book a video visit with a GP licensed in Spain, in English or Spanish. He reads your whole report, asks about exercise, medicines and symptoms, and explains whether anything needs a further check.
Does high LDH mean cancer?
Usually not. MedlinePlus says a high level does not always mean a serious condition. LDH is used in cancer care, but in a different way. In people who already have some cancers, such as lymphoma, leukaemia, myeloma, melanoma or testicular cancer, it helps show how serious the cancer is and whether treatment works.
A doctor will think about cancer only with other clues. Examples are weight loss you cannot explain, night sweats, swollen glands or an abnormal blood count.
What other results help explain a high LDH?
MedlinePlus is clear that an LDH test alone cannot show what is damaging the tissue or where. A doctor looks at the rest of your report:
- Liver tests (ALT, AST, bilirubin) point to the liver.
- A full blood count shows anaemia or changes in white cells.
- Haemolysis tests. The MSD Manual notes that red cell breakdown raises LDH and indirect bilirubin, lowers haptoglobin and often raises young red cells (reticulocytes).
- LDH isoenzymes. This test splits LDH into five forms. It can suggest which tissue the extra LDH comes from.
What does high LDH mean in pregnancy?
In late pregnancy, a high LDH can be part of HELLP syndrome. The name stands for haemolysis, raised liver enzymes and low platelets. The NHS describes it as a rare but serious liver and blood problem linked to pre-eclampsia.
The NHS lists warning signs of pre-eclampsia: a severe headache that painkillers do not ease, blurred vision or flashing lights, pain below the ribs, and sudden swelling of the face, hands or feet. These signs can also start in the weeks after birth. If you have them, go to the hospital maternity emergency unit (urgencias de obstetricia) now. Call 112 for a fit, trouble breathing or sudden loss of vision.
What happens next?
- Mild rise, you feel well, other results normal: often a repeat test in a few weeks, with no hard exercise for a few days before.
- Sample marked as haemolysed: a repeat test.
- Other results also abnormal: more tests, and sometimes a referral to a liver, blood or other specialist.
- Tiredness, yellow skin or eyes, or dark urine: see a doctor today, as this can be red cell breakdown or a liver problem.
Call 112 for chest pain, signs of a stroke (a drooping face, a weak arm or slurred speech), or severe belly pain with vomiting and feeling very unwell.
Talking it through with a doctor by video
Dr. Yelamo is a GP licensed in Spain. He sees adults, children and pregnant patients by video, every day from 07:30 to 20:30 (Spain time). In the visit he will:
- Read your full blood report, not just the LDH line.
- Ask about exercise, recent illness, symptoms and every medicine you take.
- Compare your result with the range of the lab that tested it, in Spain or abroad.
- Explain whether you need a repeat test, more tests or a specialist.
He does not promise any test or prescription before the visit. Where clinically appropriate, following a genuine evaluation. Treatment and prescriptions are issued solely at the doctor's discretion based on evidence-based clinical guidelines.
A prescription is never guaranteed: it is issued only where clinically appropriate after a genuine evaluation, as a private electronic prescription under Spanish law. This service is for urgent, non-emergency care. In an emergency, call 112.
See how the Urgent Care video visit works. It lasts 15 minutes and costs €50.
This guide is general information. It does not replace a consultation with your doctor.
Frequently asked questions
Is a high LDH serious?
Often not. Hard exercise, some medicines and a damaged sample can all raise it. A doctor reads it with your symptoms and your other results.
What is a normal LDH level?
MedlinePlus gives 125 to 220 IU/L for adults. Labs in the UK and Spain set their own ranges, so use the one printed on your report.
Can exercise raise LDH?
Yes. Intense exercise can raise LDH because muscles release it. Avoid hard training for a few days before a repeat test.
Does high LDH mean cancer?
Usually not. LDH is used to follow some cancers that are already known. On its own, a high result cannot show cancer or any other single disease.
What does a haemolysed sample mean?
Red cells broke in the tube while the blood was taken or handled. They release LDH, so the result reads falsely high. The test is usually repeated.
What is lactato deshidrogenasa on a Spanish blood test?
It is the Spanish name for LDH. It is usually shown in U/L or UI/L.
Sources
- MedlinePlus: Lactate dehydrogenase (LDH) test
- MedlinePlus: Lactate dehydrogenase test, normal range and causes
- North Bristol NHS Trust, Severn Pathology: LDH reference ranges
- MSD Manual: Overview of hemolytic anemia
- NHS: Pre-eclampsia
Related guides
Medical Citations & Sources
This content is written and reviewed by a licensed physician with reference to the following official health authorities.
