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General Chemistry

LDH

LDH is a substance that sits inside cells all over your body and leaks into the blood when cells are damaged. So a raised level is a general "something somewhere is irritated" flag, not a diagnosis on its own — it does not say where. A normal result is reassuring, and if it is up, your doctor uses other tests to pin down which part of the body is involved.

Standard Care
CategoryGeneral Chemistry
Reference range120–250 U/L U/L
Evidence✓Standard Care
Last updated3 July 2026
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What is ldh?

Lactate dehydrogenase (LDH, sometimes written LD) is an enzyme that is found in cells throughout the body — in the liver, heart, muscles, kidneys, blood cells and many other tissues. Inside cells, LDH takes part in how your body turns sugar into usable energy, switching between two molecules called pyruvate and lactate. When cells are damaged or destroyed, they release LDH into the bloodstream, causing blood levels to rise. For this reason, LDH is used as a general marker of injury to cells. It does not point to one specific organ — it simply signals that cells somewhere have been under stress.

Why is it tested?

Because LDH rises with cell damage from almost any source, it is used as a broad indicator of tissue stress. Your GP might order it as part of a general panel to get a wide-angle view of cellular health, or to monitor certain conditions where tissue breakdown is a concern. A key thing to understand about LDH: because it is non-specific, a raised level is usually a starting point rather than an answer. More specific tests — such as CK (creatine kinase, for muscle), ALT and AST (for liver), or a full blood count (for blood-cell breakdown) — help pinpoint which organ is involved when LDH is elevated.

Reference range (Australia)

120–250 U/L U/L

This is the Australasian Harmonised Reference Interval (AHRI) for serum LDH, using the IFCC lactate-to-pyruvate method, endorsed by the AACB and RCPA. There is no separate male/female range for LDH. Because LDH is a non-specific marker, it is read together with the clinical picture and more specific tests — always use the interval on your own report.

Reference intervals vary between laboratories. Always use the range printed on your own report.

What your result means

If your level is low

A lower-than-range LDH is rarely significant and does not generally require investigation. It most often reflects individual variation or laboratory method differences rather than a meaningful clinical finding.

If your level is in range

An LDH within the range on your report — 120–250 U/L for adults — suggests cells are not leaking this enzyme in unusual amounts. This is a reassuring sign that there is no obvious widespread cell stress at the time of the test.

If your level is high

A raised LDH means cells somewhere in the body have been damaged or destroyed. Because LDH is found in so many cell types, this signal is deliberately non-specific. Common causes include muscle damage or intense exercise, liver stress (from alcohol, medications or fatty liver disease), breakdown of blood cells (including from a haemolysed sample — see below), and some cancers where cells turn over rapidly. An isolated mildly raised LDH is often repeated, or followed up with more targeted tests such as CK, ALT and AST, to help narrow down the cause. Your GP will look at the full pattern of results alongside your symptoms rather than treating LDH alone as a verdict.

What can affect your result

Several things can raise LDH without necessarily pointing to a serious underlying cause. A haemolysed sample — where red blood cells are broken during blood collection or processing — can significantly raise LDH, because red blood cells contain high concentrations of the enzyme. If your result is unexpectedly high, your doctor may check whether the sample was haemolysed before drawing conclusions. Intense or unaccustomed exercise causes normal muscle-fibre breakdown and can temporarily lift LDH for a day or two. This is not a sign of injury. Genuine causes of a raised LDH include liver conditions (such as hepatitis, fatty liver or alcohol-related damage), muscle breakdown, certain blood disorders where red cells break down prematurely (haemolysis), and some cancers. Because so many conditions can raise LDH, your GP uses it as a signal to look further rather than as a diagnosis on its own.

When to act

A mildly raised LDH in isolation is often followed by a repeat test or by more specific tests — CK for muscle, ALT and AST for liver — to work out what is going on. The pattern across multiple markers, and whether LDH is stable or rising, tells a clearer story than any single reading. If your LDH is elevated alongside other abnormal results or symptoms, your GP will investigate the most likely cause based on the full picture. An isolated, mildly raised LDH with no symptoms often has a benign explanation, such as a haemolysed sample or recent vigorous exercise. This page is general information and is not a substitute for advice from your GP.

Frequently asked questions

The Australasian Harmonised Reference Interval for adults is 120–250 U/L, using the IFCC lactate-to-pyruvate method (the standard method used in Australian laboratories). There is no separate range for men and women. The interval on your own report is the one your GP uses — always check your own result against your report's reference range.

Because LDH is found in cells throughout the body, a raised level is a general signal of cell damage or destruction — it is not specific to any one organ. The main use for LDH is as a broad indication of cell damage, including muscle damage, liver damage, blood-cell damage and cancers. Because LDH sits in almost all body tissues, a raised level can also follow things like anaemia, a heart attack, fractures or an infection. If LDH is high, more specific tests such as CK, ALT and AST can help pinpoint the organs involved.

A high LDH on its own is not a diagnosis — it is a signal that tells your GP to look further. Because LDH is released by many different cell types, the elevation can range from a benign cause (a haemolysed sample, recent exercise) to something that needs follow-up. Your GP will read it alongside your other results and symptoms to decide whether more investigation is needed. Many causes of a raised LDH are straightforward and manageable once identified.

For adults, the Australasian Harmonised Reference Interval (endorsed by the AACB and RCPA) is 120–250 U/L using the IFCC lactate-to-pyruvate method. There is no sex difference in the reference interval for LDH. The interval on your own report is the most relevant guide, as it reflects the method your laboratory uses.

Because LDH is non-specific — it rises with damage to muscle, liver, blood cells and other tissues — it tells your GP that something is stressed but not exactly what. More specific tests help narrow the picture: CK (creatine kinase) is concentrated in muscle and heart, ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are concentrated in the liver. Looking at the pattern across these markers lets your GP pinpoint which organ is driving an elevated LDH.

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