Liver and pancreas
LDH
An enzyme found in almost all body cells; raised with tissue damage or with breakdown of red blood cells.
Everything about this testWhat it measures
LDH (lactate dehydrogenase) is an enzyme found in almost all cells of the body, including red blood cells, muscles, liver, heart and lungs. It helps convert lactic acid (lactate) in the energy supply of the cell. Normally there is little LDH in the blood. If cells break down somewhere, LDH is released and the value rises. The number alone does not show which tissue the LDH comes from.
- Faster breakdown of red blood cells (hemolysis)
- Tissue damage, for example to muscles, liver, heart or lungs
- The course of a known condition in which tissue is damaged or recovers
High
A slightly raised LDH often has a harmless cause. The best known is hemolysis in the tube: with a difficult blood draw, a finger prick or long transport, red blood cells break down and release LDH, while nothing is wrong in the body. Heavy exercise or strength training in the days before the blood draw and pregnancy also give higher values. A clearly raised value may fit faster breakdown of red blood cells, a vitamin B12 or folic acid deficiency, liver inflammation, muscle damage, pneumonia or another severe infection. Rarely: some forms of cancer, such as lymph node cancer (lymphoma).
Low
A low LDH has no meaning and occurs in healthy people. There is no condition that is detected with an LDH that is too low.
If your result is abnormal
With a slightly raised LDH without symptoms, the GP repeats the measurement, preferably with blood drawn from the arm and without heavy exercise in the days before. If the value stays raised, the GP looks at the blood count, bilirubin, the liver values and the muscle enzyme CK to find where the LDH comes from, and refers you to an internist (specialist in internal medicine) if needed.
Reliability
LDH is a sensitive but very non-specific value: it rises with damage to almost any tissue and does not say where the damage is or what the cause is. According to the Dutch Society for Clinical Chemistry (NVKC), other tests give faster and more sensitive information for most organs, for example troponin for the heart and ALT for the liver. LDH is therefore mainly used together with other results, for example with the blood count, bilirubin, reticulocytes and haptoglobin when faster breakdown of red blood cells is suspected. With long-lasting symptoms after COVID, according to the guideline of the Federation of Medical Specialists (FMS) and the Dutch GP association (NHG), exploratory laboratory testing does not help to show or rule out symptoms related to COVID-19.
Limitations
- Hemolysis in the tube, for example due to a difficult blood draw, a finger prick, shaking or long transport, raises LDH strongly and is a common cause of a falsely high result.
- Heavy exercise or strength training in the days before the blood draw raises the value.
- Pregnancy gives higher values; according to the NVKC, children have higher values than adults.
- Reference values differ by laboratory.
How common is this
How often a raised LDH occurs in people without symptoms is not well known. Some of the slightly raised results outside hospital are due to hemolysis in the sample or to exercise shortly before the blood draw. The conditions that clearly raise LDH, such as faster breakdown of red blood cells, are rare in the general population.
Who is this useful for
Useful as an additional value when faster breakdown of red blood cells is suspected, together with the blood count and bilirubin, and to follow the course of a condition for which the treating doctor uses LDH. With tiredness or long-lasting symptoms after COVID, LDH usually does not help to explain the symptoms. In healthy adults without symptoms, the test adds little.
Downsides and risks
- A falsely raised LDH due to hemolysis in the sample is common and, without a repeat measurement, can lead to unnecessary worry and unnecessary tests.
- Because LDH rises in many conditions, searching for the cause of a slightly raised value often yields no clear explanation.
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