LDH, or lactate dehydrogenase, is an enzyme that helps convert lactate to pyruvate in cells. It is released into the blood when cells are damaged or turn over quickly. It is ordered as a general marker in several assessments, and the reference range printed on your report is the one that applies.
The result is easy to over-read. A higher LDH says that cells somewhere are releasing the enzyme, not which cells or why, and the report usually prints it beside other results that narrow the question.
What the test measures
LDH sits in the pathway that lets cells turn lactate into pyruvate, a step in energy metabolism. It is present in cells throughout the body, including liver, muscle, red blood cells, heart, and kidney. When cells are damaged or break down faster than usual, the enzyme leaks into the blood and the measured activity rises.
Because the enzyme is everywhere, a result reflects how much has been released rather than where from. The test measures total LDH activity in serum or plasma. Some laboratories also report isoenzyme fractions, which give a rough hint about the tissue source; many do not.
Why it may be ordered
- As part of a broad assessment when a clinician is considering tissue damage or faster cell turnover.
- Alongside a blood count when red blood cell breakdown is one possibility, because red cells are rich in LDH.
- With liver tests, when liver cell injury is part of the question.
- In some cancer care, as one of several results a clinician reviews rather than as a test on its own.
- When a sample shows unexpected results and the laboratory wants to check whether cells broke during handling.
- In body fluids other than blood, where LDH is interpreted against different criteria and not against a blood range.
The test is not specific, and it does not confirm or rule out any condition. A clinician reads it with the reason it was ordered and with the rest of the report.
The unit on your report
| What you may see | Unit | What it reflects |
|---|---|---|
| LDH, LD, lactic dehydrogenase | U/L | Enzyme activity per litre of serum or plasma. The abbreviation varies by laboratory; the measurement is the same. |
| LDH, serum | U/L | LDH measured in serum. Red cells and platelets can release the enzyme while the sample clots, so serum and plasma can differ. |
| LDH, plasma | U/L | LDH measured in plasma, collected in a tube that prevents clotting. |
| LDH isoenzymes | Percent of total activity | The share of total LDH activity carried by each fraction. Not a separate measurement of a different enzyme. |
The unit is the same across most reports, but the number attached to it still depends on the method, the analyser, and the specimen. Two laboratories can both print U/L and still use ranges that do not match.
Why this page does not print a range
An LDH range belongs to the assay that produced it. Reference ranges differ by laboratory, by method, by specimen type, and by the population the laboratory used. Age, sex, and the clinical context of that population all shape where the limits sit. A range that fits one analyser may not fit another.
The range printed on the report that produced your value is the one that applies. Doctano keeps that printed range with the result rather than substituting one from another laboratory or from the internet.
What a high value can mean
A higher LDH means more enzyme activity was measured in the sample. Possible contributors include red blood cell breakdown, liver cell injury, muscle injury, some infections, some cancers, and a sample in which cells broke during collection or processing. The list is not a diagnosis, and it is not exhaustive.
Red cell breakdown is one of the more common explanations, which is why a blood count usually comes next. A higher value does not confirm or rule out any of these possibilities, and a value inside the printed range does not settle the question either.
What a low value can mean
A lower LDH is often not interpreted on its own, because the test is mainly used to notice release from cells rather than to find a shortage. A result below the printed range may simply reflect the method and the sample.
This page does not tell you whether your value is normal. If a report flags a low LDH, the clinician reads it with the rest of the results rather than in isolation.
What can move the value
- How the sample was handled. Red cells that break during collection, transport, or processing release LDH and raise the result without anything changing in the person.
- Specimen type. Serum and plasma can differ, and the report usually says which was used.
- Strenuous exercise. Intense activity can raise LDH from muscle.
- Assay and analyser. Different methods and platforms produce different numbers on the same sample.
- Red cell turnover. Conditions that break red cells down release the enzyme.
- Liver or muscle injury. Both tissues contain LDH.
- Medicines that affect the liver or muscle. A clinician can say whether a medicine could affect the result.
What to compare it with
Read LDH with a complete blood count: haemoglobin, the red cell indices, and a reticulocyte count where one was done. Haptoglobin, when the laboratory reports it, is another result clinicians read when red cell breakdown is a possibility. Liver tests such as ALT, AST, and bilirubin give context when the liver is a candidate source.
The most useful comparison is the previous LDH from the same laboratory, measured on the same specimen type. A value that moved between two laboratories, or between serum and plasma, is weaker evidence than the same test repeated the same way.
How to see the trend
Doctano reads the LDH value, its unit, and the reference range printed on the report. It keeps the range with the result, lines the value up with earlier LDH results on the profile's timeline, and every point opens the report it came from.
Because LDH is sensitive to sample handling, a single higher value is a prompt to check the report's remarks and the rest of the panel, not a conclusion. The trend across properly collected samples is the more useful signal.
What this page is not
This page explains the test in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the value and the unit against the original report, and discuss the result with a qualified professional.