Generality
Lactate dehydrogenase ( LDH ) is an enzyme found in most cells in the body. Its main task is to metabolize glucose to make it energy usable.
Lactate dehydrogenase is found in numerous tissues, but is concentrated mainly in the skeletal muscles, liver, heart, kidneys, pancreas and lungs.
When the cells are damaged or destroyed, the LDH enzyme is released into the liquid fraction of the blood (serum or plasma), as well as increasing its concentration in other biological liquids (eg liquor) in the presence of certain diseases. Therefore, LDH is a general indicator of tissue and cellular damage .
What's this
Biological role and types of LDH
Lactate dehydrogenase (LDH or lactic acid dehydrogenase) is a cytoplasmic enzyme with a wide distribution in tissues, where it catalyzes the interconversion of lactate to pyruvate.
Lactate dehydrogenase is a tetramer with subunits belonging to two different types which, combining differently together, give rise to five different isoenzymes: LDH1 and LDH2 are elevated in the heart and erythrocytes, while LDH 4 and LDH 5 are elevated in the liver and in the muscle;
- LDH1 is prevalent in the myocardium, red blood cells, kidney and germ cells;
- LDH2 is prevalent in the myocardium and red blood cells, as well as being concentrated in white blood cells and kidneys (where it is present in lower concentrations than LDH1);
- LDH3 is prevalent in the lungs and other tissues;
- LDH4 is found skeletal muscle, in the liver (where it is present in lower concentrations than LDH5), in lymph nodes and in white blood cells;
- LDH5 is characteristic in the liver and skeletal muscle.
This tissue specificity makes the lactate dehydrogenase assay of great clinical interest to assess the site of hypothetical tissue damage.
LDH and Infarct
Under normal conditions, lactate dehydrogenase 1 prevails over LDH2, whereas after a heart attack the latter tends to prevail; compared to transaminases and creatine kinases, after a heart attack lactate dehydrogenase values increase later (24-72 hours) and reach maximum values within 3-4 days, to then return to normal within a few weeks.
Thanks to this feature, the dosage of lactate dehydrogenase allows a late diagnosis of myocardial infarction, sometimes exceeded by the patient almost without realizing it.
Why do you measure
The blood LDH dosage is indicated in the following cases:
- As a general indicator of the presence and severity of acute or chronic tissue damage ;
- To determine and monitor progressive diseases, such as anemia (including hemolytic and megaloblastic forms) or serious infections ;
- As a support in staging and / or monitoring of treatment (eg chemotherapy) of neoplastic processes (eg some types of testicular and ovarian tumors, lymphoma, leukemia, melanoma and neuroblastoma).
Furthermore, lactate dehydrogenase can be dosed onto other biological liquids for the purpose of:
- Distinguish between bacterial or viral meningitis;
- Evaluate other fluids, such as pleural, peritoneal or pericardial;
- Understanding whether the accumulation of liquid is due to damage and inflammation (exudate) or of an imbalance of pressure inside the vessels and to the concentration of proteins in the blood (transudate).
If the LDH is increased, other tests are prescribed (such as ALT, AST or ALP) as a support in the diagnosis and determination of the organ involved. Once the acute or chronic problem has been identified, the parameter can be measured at regular intervals to monitor its course and / or resolution.
All this information is particularly useful in choosing the most appropriate therapeutic approach.
Normal values
The normal LDH values are between 80 and 300 mU / ml .
Note : the reference interval of the exam can change according to age, sex and instrumentation used in the analysis laboratory. For this reason, it is preferable to consult the ranges listed directly on the report. It should also be remembered that the results of the analyzes must be assessed as a whole by the general practitioner who knows the patient's medical history.
LDH High - Causes
High concentrations of lactate dehydrogenase indicate that some types of tissue are damaged. Usually, the value of the enzyme increases when cellular destruction begins, reaching maximum concentration after a certain period of time, and then decreases.
An increase in LDH can be observed in the presence of:
- Hemolytic anemia;
- Pernicious anemia;
- Infections (mononucleosis, meningitis, encephalitis, HIV etc.);
- Sepsis;
- Intestinal and pulmonary infarction;
- Acute kidney disease;
- Acute liver disease;
- Acute muscle damage;
- Pancreatitis;
- Bone fractures;
- Testicular cancer, lymphoma or other types of cancer.
In people with chronic and progressive diseases, a moderately high concentration of LDH may persist.
LDH Low - Causes
Low or normal values of lactate dehydrogenase do not generally indicate a problem.
In some cases, reduced concentrations can be observed when the person has ingested large amounts of ascorbic acid (vitamin C).
How to measure it
The lactate dehydrogenase test is performed through a simple blood sample, usually taken in the morning.
Sometimes, a specific procedure is required to collect a sample of liquid in a particular area of the body (eg cephalorachidian, pleural, peritoneal, etc.).
Preparation
Before undergoing blood sampling, it is necessary to observe a fast of at least 8-10 hours. During this period, it is only possible to take a small amount of water.
Interpretation of Results
- The serum increase in LDH can occur in all pathological conditions characterized by the development of irreversible cellular damage (necrosis), with loss of the cytoplasmic content.
- When there is an increase in lactate dehydrogenase in the liquor, it is possible to define the bacterial origin of meningitis, while normal or low concentrations indicate the probable viral origin.
- High concentrations of LDH indicate that there is an exudate in the pericardial, peritoneal or pleural fluid, while low concentrations indicate the presence of a transudate.
| POSSIBLE CAUSES | CONSIDERATIONS |
| Despite the large presence in the tissues, due to the cytoplasmic localization, lactate dehydrogenase is present in the blood in very small concentrations. Total LDH levels increase significantly in all situations where generic tissue damage is produced. To obtain further clinical indications on the organs or tissues involved, it is necessary to evaluate additive blood parameters, and / or rely on the evaluation of the individual isoforms (see in-depth article on the interpretation of blood levels of LDH). |
To learn more: Lactate dehydrogenase: interpretation of the results »
