Lactate Dehydrogenase (LDH): Tissue Stress, Recovery, and Inflammation Signal
Overview
Lactate Dehydrogenase (LDH) is an enzyme found in many tissues, including muscle, liver, blood cells, and lungs. When cells are stressed or damaged, more LDH can leak into the bloodstream, so a higher level often means there has been some recent tissue injury or inflammation. In this glossary you will see what the LDH test actually measures, how it fits alongside markers like Creatine Kinase (CK), liver enzymes such as ALT, and inflammation markers like C-Reactive Protein (Standard CRP), how to think about high and low results, what can nudge LDH over time, and when it is worth going through the number with a clinician.
What LDH is and why it matters
Lactate Dehydrogenase is an enzyme that helps cells handle energy production, especially when oxygen supply is limited or demand is high. It is present in many tissues, including:
Skeletal muscle
Heart muscle
Liver
Red blood cells
Lungs and other organs
The LDH blood test measures how much of this enzyme is circulating in your blood. Under normal conditions, only small amounts are present. When cells are damaged or break down more than usual, LDH can leak into the bloodstream and levels can rise.
Because LDH is so widely distributed, it is not specific to one organ, but it can be a useful general signal that the body has been under some form of stress or injury.
What your LDH result can tell you
Your LDH value can help answer questions like:
Is there a broad signal that some tissue or organ is under stress or has been injured
Does this fit with known issues such as muscle damage, liver disease, hemolysis, infection, or recent surgery
How does this result line up with more specific markers like CK for muscle, ALT for liver, or CRP for inflammation
A moderately or clearly raised LDH supports the idea that cells have been breaking down more than usual. It does not tell you where, but when viewed with symptoms and other labs it can reinforce the pattern of muscle injury, liver stress, blood cell breakdown, or systemic inflammation. A normal LDH is reassuring that there is no strong global tissue damage signal at the time of testing.
How to read high and low LDH
LDH is most useful when it is higher than expected. Low values are rarely a concern.
When LDH is high
Higher LDH can mean:
muscle injury or heavy tissue stress, especially when CK is also raised
liver cell injury, often together with abnormal liver enzymes
breakdown of red blood cells, called hemolysis
lung, heart, or other organ involvement during severe illness
recent surgery, trauma, or intense infection causing more cell turnover
People with high LDH may notice symptoms that match the underlying issue, for example muscle soreness and weakness after major muscle injury, abdominal discomfort and fatigue with liver problems, or chest symptoms and breathlessness with serious lung involvement, rather than symptoms from LDH itself.
The level of LDH does not always tell you how severe the situation is, but very high or rising values usually prompt clinicians to look carefully for ongoing tissue damage or uncontrolled inflammation.
When LDH is low or in range
A normal LDH usually suggests:
there is no strong, ongoing pattern of widespread cell damage at the time of the test
Very low LDH is rare and typically not clinically important. The main focus is on whether LDH is clearly and persistently elevated, especially when it matches concerning symptoms or other abnormal tests.
What can affect your LDH result
LDH responds to how much cell damage or turnover is happening and to how blood and samples are handled. Common influences include:
Muscle and heart stress
Intense exercise, muscle injury, or heart muscle damage can all raise LDH, especially when paired with a high Creatine Kinase (CK) and matching symptoms.Liver and blood cell health
Liver conditions that injure liver cells and processes that break down red blood cells more quickly than normal can both increase LDH. In these cases, LDH is interpreted together with ALT, AST, bilirubin, and a full blood count.Infection and inflammation
Severe infections, inflammatory diseases, and some cancers can raise LDH as cell turnover and tissue stress increase. In these settings, LDH often travels with other markers like CRP and changes in blood counts.Recent procedures or trauma
Surgery, biopsies, or physical trauma can cause a temporary LDH rise as tissues heal.Sample handling
If red blood cells break in the tube after blood is drawn, LDH can appear falsely high. This is one reason why a repeat test is sometimes ordered when a result does not fit the clinical picture.
Because LDH is non specific, trends over time and the combination of LDH with more targeted tests are usually more helpful than a single value on its own.
When to talk to a clinician about LDH
You should review your LDH result with a clinician when:
LDH is clearly above the reference range or rising on repeat tests
You have symptoms such as unexplained fatigue, muscle weakness, chest pain, shortness of breath, abdominal pain, or night sweats
You are being monitored for a known condition such as liver disease, muscle disease, hemolysis, cancer, or autoimmune disease and LDH is part of that tracking
LDH is high but you are not sure what part of the body it might be coming from
A clinician can place LDH alongside CK, liver enzymes like ALT and AST, blood counts, inflammatory markers, imaging, and your symptom story. From there they can decide whether the result mostly reflects recent exercise or mild stress, or whether it points toward muscle, liver, blood, lung, or systemic issues that need further work up or treatment.
Lactate Dehydrogenase (LDH) in one view
Lactate Dehydrogenase is a broad stress signal that rises when cells in muscle, liver, blood, or other tissues are being injured or turned over more than usual. On its own it does not tell you where the problem is, but a clearly elevated LDH, especially when it matches symptoms and other abnormal labs, is a nudge to look deeper. Used together with CK, liver enzymes, CRP, blood counts, and imaging, LDH becomes a practical marker for tracking tissue stress, recovery, and how well treatment is calming inflammation and damage with a clinician’s guidance.
