What is LDH?
LDH (lactate dehydrogenase) is an enzyme involved in lactic acid fermentation. With the help of this process, cells obtain energy from blood sugar (glucose) without the need for oxygen.
LDH is present in all cells: The highest enzyme activity can be detected in skeletal muscle, cardiac muscle, kidneys, brain and liver.
The enzyme is located inside the cells. If these are destroyed, LDH is released and can be measured in the blood. An elevated LDH laboratory value therefore indicates that cells have perished somewhere in the body.
Because lactate dehydrogenase is found in so many tissues, it is a non-specific marker that can be elevated in many diseases.
Different variants of LDH
Lactate dehydrogenase is composed of four subunits, of which there are two types: the H-type (heart) and the M-type (muscle). Depending on the combination, this results in five different LDH isoenzymes.
The five LDH isozymes are:
- LDH-1: with four H-type subunits (H4). Share of total LDH 15 to 23 percent. Main occurrence: mainly heart muscle, but also red blood cells (erythrocytes) and kidneys.
- LDH-2: with three H-type subunits and one M-type subunit (H3M). Accounts for 30 to 39 percent of total LDH. Main occurrence: Erythrocytes, kidneys, heart and lungs.
- LDH-3: with two H- and two M-type subunits (H2M2). Proportion of total LDH 20 to 25 percent. Main occurrence: Lung, platelets (thyromobocytes) and lymphatic system.
- LDH-4: with one H-type subunit and three M-type subunits (HM3). Share of total LDH 8 to 15 percent. Main occurrence: various organs.
- LDH-5: with four M-type subunits (M4). Share of total LDH 9 to 14 percent. Main occurrence: mainly skeletal muscle, but also liver.
When is LDH determined?
LDH-1 in focus in suspected heart attacks
The body breaks down the different types of lactate dehydrogenase at different rates. For example, half of LDH-5 is broken down after just eight to twelve hours, while half of LDH-1 – which is mainly found in the heart muscle – is only broken down after three to seven days.
LDH-1 thus remains significantly elevated the longest after an acute myocardial infarction and is thus suitable for late diagnosis: the isoenzyme can indicate a myocardial infarction up to the 10th to 14th day thereafter. In this case, the proportion of this isoenzyme is usually more than 45 percent of the total lactate dehydrogenase.
Newer parameters in cardiac medicine are, for example, troponin T or troponin I. They can be detected in the blood up to seven to ten days after an infarction and are more sensitive for a heart attack than LDH. However, if the aim is to detect a heart attack that is no longer fresh, the detection of lactate dehydrogenase may be necessary.
Suspicion of other diseases
Physicians also determine lactate dehydrogenase as an additional marker in:
- certain forms of anemia (anemia)
- diseases of the skeletal muscles
- Liver diseases
- Poisonings
- pulmonary embolism
- malignant tumors
LDH reference values
The blood value LDH is determined in the blood serum. Depending on age and sex, the following LDH normal values apply:
|
Age |
Male |
female |
|
up to 30 days |
178 – 629 U/l |
187 – 600 U/l |
|
31 days to 3 months |
158 – 373 U/l |
152 – 353 U/l |
|
4 to 6 months |
135 – 376 U/l |
158 – 353 U/l |
|
7 to 12 months |
129 – 367 U/l |
152 – 327 U/l |
|
1 to 3 years |
164 – 286 U/l |
164 – 286 U/l |
|
4 to 6 years |
155 – 280 U/l |
155 – 280 U/l |
|
7 to 9 years |
141 – 237 U/l |
141 – 237 U/l |
|
10 to 11 years |
141 – 231 U/l |
129 – 222 U/l |
|
12 – 13 years |
141 – 231 U/l |
129 – 205 U/l |
|
14 to 19 years |
117 – 217 U/l |
117 – 213 U/l |
|
from 20 years |
100 – 247 U/l |
120 – 247 U/l |
The abbreviation “U/l” stands for enzyme unit per liter.
When is the LDH value elevated?
If the LDH is too high, this can have various reasons:
LDH is also elevated in intravascular hemolysis (destruction of red blood cells within the vessels) and infectious mononucleosis (glandular fever).
Heart damage: The isoenzyme LDH-1 is particularly elevated in heart disease, for example in myocardial infarction, myocarditis, pericarditis, endocarditis or cardiac arrhythmias.
Lactate dehydrogenase is also elevated in cellular damage following diagnostic and therapeutic procedures on the heart.
Skeletal muscle diseases: LDH-5 is elevated in skeletal muscle diseases or damage. These include muscular dystrophy, storage diseases, muscle inflammation, injury, and toxic muscle damage.
Other causes: In addition, LDH may be elevated in pulmonary embolism (LDH-3) and in malignant tumors.
Falsely high values (without disease values) are measured in:
- hemolysis (disintegration of blood cells) in the blood sample
- physical stress
What to do if the LDH value changes?
An elevated lactate dehydrogenase value is often difficult to interpret because it can occur in very many diseases. Therefore, further clinical examinations or laboratory parameters are necessary to clarify the exact cause of the altered blood values.
The LDH value can also be elevated after heavy physical work or sport or after a difficult blood collection and then has no clinical value. It is therefore advisable to repeat the blood collection if LDH is elevated.