LDH - Lactate dehydrogenase isoenzymes test
The enzyme lactate dehydrogenase (also known as lactic dehydrogenase, or LDH) is found
in the cells of almost all body tissues. The enzyme is especially concentrated in the
heart, liver, red blood cells, kidneys, muscles, brain, and lungs. The total LDH can be
further separated into five components or fractions labeled by number: LDH-1, LDH-2,
LDH-3, LDH-4, and LDH-5. Each of these fractions, called isoenzymes, is used mainly by a
different set of cells or tissues in the body. For this reason, the relative amounts of a
particular isoenzyme of LDH in the blood can provide valuable diagnostic information.
Why is LDH - Lactate dehydrogenase isoenzymes test performed
The LDH isoenzymes test assists in differentiating heart attack, anemia, lung injury,
or liver disease from other conditions that may cause the same symptoms (differential
diagnosis).
How is LDH - Lactate dehydrogenase isoenzymes test
performed
LDH is found in the cells of almost all body tissues. When certain conditions injure
cells in tissues containing LDH, it is released into the bloodstream. Because LDH is so
widely distributed throughout the body, analysis of total LDH will not help make a
diagnosis of a particular disease. Because this enzyme is actually composed of five
different isoenzymes, however, analysis of the different LDH isoenzyme levels in the blood
can help in the diagnosis of some diseases.
The five LDH isoenzymes are: LDH-1, LDH-2, LDH-3, LDH-4, and LDH-5. In general, each
isoenzyme is used mostly by the cells in a specific tissue. LDH-1 is found mainly in the
heart. LDH-2 is primarily associated with the system in the body that defends against
infection (reticuloendothelial system). LDH-3 is found in the lungs and other tissues,
LDH-4 in the kidney, placenta, and pancreas, and LDH-5 in liver and striated (skeletal)
muscle. Normally, levels of LDH-2 are higher than those of the other isoenzymes.
Certain diseases have classic patterns of elevated LDH isoenzyme levels. For example,
an LDH-1 level higher than that of LDH-2 is indicative of a heart attack or injury;
elevations of LDH-2 and LDH-3 indicate lung injury or disease; elevations of LDH-4 and
LDH-5 indicate liver or muscle disease or both. A rise of all LDH isoenzymes at the same
time is diagnostic of injury to multiple organs. For example, a heart attack with
congestive heart failure may cause symptoms of lung and liver congestion. Advanced cancer
and autoimmune diseases such as lupus can also cause this pattern.
One of the most important diagnostic uses for the LDH isoenzymes test is in the
differential diagnosis of myocardial infarction or heart attack. The total LDH level rises
within 24-48 hours after a heart attack, peaks in two to three days, and returns to normal
in approximately five to ten days. This pattern is a useful tool for a delayed diagnosis
of heart attack. The LDH-1 isoenzyme level, however, is more sensitive and specific than
the total LDH. Normally, the level of LDH-2 is higher than the level of LDH-1. An LDH-1
level higher than that of LDH-2, a phenomenon known as "flipped LDH," is
strongly indicative of a heart attack. The flipped LDH usually appears within 12-24 hours
after a heart attack. In about 80% of cases, flipped LDH is present within 48 hours of the
incident. A normal LDH-1/LDH-2 ratio is considered reliable evidence that a heart attack
has not occurred. |