Liver and pancreas
LDH-isoenzymen
Distribution of the enzyme LDH over five forms; gives a hint about which tissue a raised LDH comes from.
Everything about this testWhat it measures
LDH (lactate dehydrogenase) is an enzyme found in virtually all cells. When cells break down, LDH enters the blood. There are five forms, LD1 to LD5, and each tissue has its own mix: LD1 and LD2 are mainly in heart muscle and red blood cells, LD3 in the lungs and other organs, LD4 and LD5 mainly in the liver and skeletal muscles. The laboratory separates the forms and measures the share of each; that gives a clue about which tissue a raised LDH comes from.
- The source of a raised total LDH: red blood cells or heart, or instead liver and muscles
- Breakdown of red blood cells (hemolysis)
High
A raised share of LD1 and LD2 fits breakdown of red blood cells or damage to the heart muscle. A raised share of LD4 and LD5 fits a liver disease or muscle damage, for example after heavy exercise. A raised LD3 can occur with lung conditions. Rarely, an abnormal pattern goes together with a malignant condition. The isoenzymes say something about the possible source, but not about the cause or the severity.
Low
A low share of one of the forms usually has no meaning, because the distribution then mainly shifts to another form. A low total LDH causes no symptoms. Very rarely, there is an inherited deficiency of one of the building blocks of the enzyme, which sometimes causes muscle symptoms during exercise.
If your result is abnormal
With an abnormal pattern, the GP looks at the specific tests for the tissue involved, such as ALT and AST, CK, the blood count with reticulocytes and bilirubin, and repeats the measurement if needed without prior exercise. With signs of breakdown of red blood cells or heart damage, you are referred to an internist (specialist in internal medicine) or cardiologist.
Reliability
The distribution only gives a rough clue about the source of a raised LDH. According to the Dutch Society for Clinical Chemistry (NVKC), better and more specific tests are available for virtually all uses: troponin for the heart, ALT and AST for the liver, CK for muscles, and haptoglobin, bilirubin and reticulocytes for breakdown of red blood cells. With a normal total LDH, a shift in the distribution says little. There are no well-standardized cut-off values for the distribution itself.
Limitations
- Breakdown of red blood cells during or after the blood draw, for example due to a tourniquet left on for a long time or shaking, raises LD1 and LD2 and can mimic a heart or blood problem.
- Heavy exercise in the days before the blood draw mainly raises LD4 and LD5.
- The sample must stay at room temperature; cold mainly breaks down LD4 and LD5.
- Separation method and reference values differ by laboratory.
How common is this
A slightly raised LDH occurs regularly in healthy people, for example after exercise or due to the blood draw. There are no Dutch figures on how often an abnormal distribution of the isoenzymes occurs.
Who is this useful for
The result mainly means something with a raised total LDH whose source remains unclear after the usual liver, muscle, heart and blood tests. In people without symptoms and with a normal total LDH, the distribution says little.
Downsides and risks
- An abnormality due to the blood draw or exercise can cause unnecessary worry or lead to unnecessary further testing.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results