A Raised LDH with Nothing Else Abnormal
LDH is present in nearly every tissue in the body, which makes it the least specific enzyme on any panel. Raised on its own, with normal liver enzymes and a normal CK, it most often means red cells broke down — and far more often in the tube than in the person. It cannot point anywhere by itself, which is why it is rarely worth requesting alone.
The pattern on your report
- LDH High Key
- ALT Normal Key
- CK Normal Key
- Haptoglobin Normal Key
Printed as: ALT in U/L— A normal value takes the liver out of the picture.CK in U/L— A normal value takes muscle out, provided it was measured after several days without strenuous exercise.Haptoglobin in g/Lor mg/dL— Consumed when free hemoglobin is released, so a low value points at destruction inside the body.LDH in U/L— Present in nearly every tissue, and reference ranges differ between analyzers more than for most enzymes.
Why the numbers look like this
The enzyme takes part in a basic energy-producing reaction that every cell performs, so every cell contains it. Liver, heart, muscle, kidney, lung, red cells and lymph nodes all release it when damaged, and the blood level rises without saying which of them did.
Red cells hold a great deal of it, which is why they dominate the explanations. Cells ruptured during a difficult draw release it directly into the sample, and that accounts for a large share of raised values in people who are entirely well. Destruction happening inside the body does the same thing but means something.
The second group is tissue turnover. Rapidly dividing tissue releases the enzyme as cells die and are replaced, so lymphomas and some other cancers produce a raised level. It gauges how much disease is present; it does not find it.
A third group is tissue death from loss of blood supply, in the bowel, lung or kidney, where the level rises alongside a person who is unwell.
One pattern deserves a mention because it is striking. In B12 or folate deficiency severe enough to affect the marrow, developing red cells die before they leave it, and the LDH released can reach levels that look alarming while the diagnosis is entirely benign and treatable.
Not being flagged is not the same as normal
Because the enzyme comes from everywhere, the size of the rise carries more information than its presence. A value marginally above the range with everything else normal, in a well person, is close to meaningless and usually reflects the sample. A markedly raised value in someone with symptoms is a different matter. Analyzers also differ substantially in their reference ranges for this enzyme, more than for most, so comparing a value against another laboratory's range misleads readily.
What else on the report can hide this
Start by asking whether the laboratory recorded the sample as hemolyzed, and take another one from an easier vein if it did. That accounts for a great many of these.
Haptoglobin is the most useful next test. Low alongside a raised LDH means red cells are being destroyed in the body, and the reticulocyte count and bilirubin complete that picture.
A full blood count with a film covers both the destruction question and the marrow one, and it will show the large cells and hypersegmented neutrophils of a B12 or folate deficiency.
Where the person is unwell, the enzyme adds little and the assessment belongs to the symptoms. Abdominal pain with a raised LDH is about the abdomen, not the enzyme.
Where it is persistently raised in someone with weight loss, night sweats or enlarged lymph nodes, that combination prompts looking for lymphoma; the number alone never would.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
Red cells ruptured in the tube
A difficult draw releases the enzyme directly into the sample. Usually flagged, and it accounts for a large share of raised values in well people.
- Very common
A marginally raised value in a well person
The enzyme comes from everywhere, so a small excess with everything else normal is close to meaningless.
- Common
Red cell destruction in the body
A low haptoglobin alongside, with a raised reticulocyte count and unconjugated bilirubin. This is the version that means something.
- Common
Recent strenuous exercise
Muscle releases it, though the CK usually rises more and falls faster. A rest before repeating clarifies it.
- Common
B12 or folate deficiency
Developing red cells die inside the marrow, and the level released can look alarming while the diagnosis is benign and treatable.
- Common
A recent viral illness
Infectious mononucleosis in particular raises it, alongside abnormal lymphocytes on the film.
- Uncommon
Lymphoma or another cancer
Rapid cell turnover releases it. Used to gauge how much disease is present rather than to find it, and the accompanying symptoms are what prompt looking.
- Uncommon
Tissue death from loss of blood supply
Bowel, lung or kidney. The person is unwell, and the assessment belongs to the symptoms rather than the enzyme.
- Rare
Macro-LDH
The enzyme bound to an antibody and cleared slowly, exactly as happens with AST. Benign, persistent, and the laboratory can identify it.
What is usually checked next
- Check the laboratory's hemolysis comment Accounts for a great many of these, and a second sample from an easier vein settles it.
- Haptoglobin Low alongside a raised LDH means red cells are being destroyed in the body rather than in the tube.
- Full blood count with a film Covers destruction and the marrow, and it shows the changes of a B12 or folate deficiency.
- B12 and folate A deficiency severe enough to affect the marrow produces a striking LDH with a benign explanation.
- A symptom review before pursuing the enzyme Where someone is unwell the assessment belongs to the symptoms, and the enzyme adds little to it.
When to seek care sooner
- Emergency Severe abdominal pain, particularly out of proportion to examination
- Emergency Sudden breathlessness or chest pain
- Same day Dark or cola-colored urine with pallor
- Soon Drenching night sweats, weight loss, or enlarged lymph nodes
- Soon A falling hemoglobin alongside
- Soon Numbness or unsteadiness with a large-cell anemia
Questions worth bringing to your appointment
- Was the sample recorded as hemolyzed?
- Has my haptoglobin been checked?
- Are my blood count and film normal?
- Have B12 and folate been tested?
- Does this number mean anything on its own?