LDH too high: muscle damage, your tube, or something else

If your LDH is too high, cells have broken down somewhere in your body. The number by itself says little more. LDH is an enzyme that sits in virtually every cell. At most labs the upper limit is around 250 U/l.

Any cell that breaks, anywhere, releases some of it.

That makes this the least specific value on your whole result. The question is never "is my LDH high", but "what is high next to my LDH". Two combinations explain almost everything in athletes, and they point in opposite directions.

What exactly is LDH?

Lactate dehydrogenase (LDH) helps your cells turn sugar into energy. That matters most when little oxygen is available. The enzyme sits in your muscles, liver, heart, kidneys, lungs and red blood cells. As long as your cells are intact, it stays inside them.

If your lab measures LDH in the blood, cell contents were released somewhere.

Your lab result calls lactate dehydrogenase LDH or LD. Those are the same substance and the same measurement, just two spellings. The LDH values per laboratory are on our LDH (lactate dehydrogenase) page.

What does a high LDH mean?

It means cells have broken down, without the number telling you which ones. The main sources in a healthy, hard-training adult are muscle tissue and red blood cells. In illness the liver, heart and marrow can contribute. You then see that in the rest of the result.

So this is a signpost, not a destination.

The top two rows cover most raised results in athletes. They look identical on the LDH line and mean completely different things.

LDH iso-enzymes: which tissue is it?

LDH comes in five forms, LDH-1 through LDH-5. Every tissue has its own mix of those forms. In theory the iso-enzymes therefore point to the source.

For you the two ends of that row matter most. LDH-1 belongs to your red blood cells, LDH-5 to your skeletal muscle. Those are exactly the two sources in the table above.

Even so, your GP rarely orders the iso-enzymes. Other tests point the right way faster and more precisely. Your CK already does that job here.

Does resistance training raise your LDH?

Yes, and eccentric training most strongly. Slowing a weight down stretches your muscle fibres under tension. The same happens running downhill and in the lowering phase of a squat. That movement produces the most microdamage. Research on eccentric loading measured both creatine kinase and LDH as damage markers (PMID 24519446, PMID 16714113).

The peak is not on the day itself. LDH rises more slowly than CK and stays up longer, often for several days after the session.

Say you do a heavy leg workout on Monday and draw on Wednesday morning. Your LDH then reads 310 U/l and your CK 640 U/l. That is the muscle damage pattern, and it settles on its own.

How to read your CK by itself is in high CK explained.

When is a high LDH simply the tube?

When your red blood cells broke during the draw or in transit. Red cells are full of LDH and full of potassium. Those two rise together while your CK stays normal. A tourniquet applied too tightly is already enough. So is too fine a needle or a long trip to the lab.

This is called haemolysis, and it is a sample problem, not a body problem.

External quality assessment rounds show that lab values differ in measurement performance. That varies by test and by concentration. It underlines how much a clean repeat matters (PMID 31339849).

Many labs actively flag haemolysis on the result. If that note is there, do not read your LDH as a finding. Treat it as a reason to draw again.

Can running itself raise your LDH?

Yes, through red blood cell breakdown in your feet. At every footstrike red cells are mechanically damaged, and they release their LDH into your plasma. Research compared running and cycling at equal exertion. After running, free haemoglobin rose fourfold more steeply (PMID 12391035).

So this route produces a genuine, body-derived rise, unlike haemolysis in the tube.

You recognise it by its company: a low haptoglobin, a mildly raised bilirubin and sometimes more reticulocytes. For that, read high reticulocyte count and high bilirubin.

How high is LDH in cancer?

In some cancers LDH is raised, because tumour cells consume a lot of sugar. There is no fixed threshold that goes with it. Doctors mainly use the value to follow a treatment, most often in lymphoma and melanoma.

Do not turn that reasoning around. A raised LDH in a healthy athlete almost always comes from muscle tissue or red blood cells.

LDH is not a cancer test and is not used as one. A full clinical picture always belongs around it. If you are worried, discuss your result with your GP.

When should you discuss a raised LDH with your GP?

Discuss it when the value stays raised on a clean repeat. That means no training in the preceding 72 hours and no haemolysis flag. It matters especially alongside abnormalities in your blood count, liver values or kidney values. Also with symptoms that stand apart from it: unintended weight loss, fever, night sweats or persistent fatigue.

Thuisarts describes an abnormal blood result as a reason to look further. It is not a diagnosis. The NHG guidelines approach non-specific enzyme values through the same pattern thinking. RIVM points out that reference values differ per laboratory. That matters extra here, because labs use different methods. Their upper limits differ too.

Take your whole result. With this value the company it keeps is literally the direction of the diagnosis.

Where do you start?

Find your CK and your potassium before you do anything else. Put them next to your LDH. That trio usually answers the question at a glance. Then check whether the lab flagged haemolysis. Only then repeat, at least 72 hours after your last heavy session.

Our complete blood count test gives you your result with an assessment by a BIG-registered doctor.

The broader context is in the complete biomarker guide for athletes. For the other value that is more often an artefact than a finding, read MCHC blood value. And if dark urine comes with a heavy session, read dark urine after training.

References

1. Muscle damage responses and adaptations to eccentric-overload resistance exercise in men and women. European Journal of Applied Physiology. 2014. PMID 24519446.
2. The effects of muscle damage following eccentric exercise on gait biomechanics. Gait and Posture. 2007. PMID 16714113.
3. Telford RD, Sly GJ, Hahn AG, et al. Footstrike is the major cause of hemolysis during running. Journal of Applied Physiology. 2003. PMID 12391035.
4. Molina A, Alcaraz J, Guiñón L, et al. Study of the analytical performance at different concentrations of hematological parameters using Spanish EQAS data. Clinical Chemistry and Laboratory Medicine. 2019. PMID 31339849.
5. RIVM. Blood testing and reference values. Accessed 2026.
6. NHG. Dutch College of General Practitioners, laboratory diagnostics in primary care. Accessed 2026.
7. Thuisarts. My blood result is abnormal. Accessed 2026.
8. Kanker.nl. LDH values. Accessed 2026.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. For treatment decisions, discuss your results with your GP.