Normal LDH level in the blood

Each laboratory must establish its own normal ranges for LDH in the blood. These ranges depend on the makeup of the local population, the technologies used and the accuracy of the measurement. There may be also slight differences in the normal levels, according to age, gender, race or ethnic origin, geographic region, diet, type of sample and other relevant status.

Your doctor will study the results along with your medical record, screenings, physical condition, symptoms and any other relevant information about your situation.

The normal ranges of LDH in the blood may be very different from lab to lab depending on the technique and the temperature at which it is measured. One of the most used methods follows the IFCC standard at 37ºC and it is the one explained in this guide. In case your test is performed at a different temperature (for example 30ºC) or with a different technique, the normal range may differ. For that reason, it is very important to check the normal range that appears in your report.

Besides, LDH may be measured in different fluids such as urine or cerebral spinal fluid (CSF). In the CSF, the normal range is approximately a 10% of the amount in the blood. An elevation of LDH in CSF is a sign of bacterial meningitis.

LDH (lactate dehydrogenase), also called lactic acid dehydrogenase or LD, is a hydrogen transfer enzyme, from the oxidoreductase family, that catalyzes the reversible conversion of lactic acid to pyruvic acid. For this reason, it plays an important role in the regulation of the body's energy.

LDH is found in many body tissues of the body particularly heart, liver, skeletal muscle, kidney and RBCs (Red Blood Cells). It is also present in other organs such as the kidneys, pancreas, spleen, brain, and lungs.

LDH is found in the form of isoenzymes based on their electrophoretic mobility. There are five main isoenzymes being each one primarily from a different organ:

• LDH1 (17 to 27% of total LDH): It is primarily from the heart and erythrocytes (RBC).
• LDH2 (23 to 38% of total LDH): It comes mostly from the reticuloendothelial system.
• LDH3 (18 to 28% of total LDH: It is from the lungs.
• LDH4 (5 to 15% of total LDH): It comes from the placenta, kidneys, and pancreas.
• LDH5 (5 to 15% of total LDH): It is largely from the liver and striated muscle.

In a normal situation, LDH2 is the isoenzyme that contributes more to the total LDH.

A LDH blood test is usually used as an indicator of tissue damage. When tissues are damaged, they release LDH isoenzymes into the bloodstream depending on the location and severity of the injury.

Therefore, an increase of LDH in the blood is a pathological condition that occurs when tissues are damaged. A serum LDH increase may be related to myocardial infarction, liver diseases, pernicious anemia, megaloblastic anemia, renal diseases, malignant diseases, and progressive muscular dystrophy.

A total LDH increase is not specific for any disease and it is necessary to know the isoenzyme causing the increase to give a more appropriate diagnosis.

For example, myocardial infarctions and hemolytic anemias tend to cause elevations in LDH1 and LDH2, LDH3 is elevated in pulmonary infarction while LDH5 is usually elevated due to liver disorders. Malignant tumors, in general, cause increases in LDH2, LDH3 and LDH4.

LDH levels below the normal range are rare and give usually no medical information. However, there are some genetic disorders related to a low LDH level in the blood. A decrease in the LDH level during a cancer treatment is usually a positive sign.

The following values are considered to be normal values:

IMPORTANT: These levels are expressed in UI/l. They are an example of a healthy man of about 45 years old with no known disease and not taking any medication. The ranges can be different depending on the laboratory or on your personal circumstances.