Aldolase is present most
significantly in skeletal and heart muscle. Damage to skeletal muscle produces
high serum levels of aldolase, particularly in the case of progressive muscular
dystrophy. Aldolase may also be slightly increased in early stages of viral
hepatitis and advanced cancer of the prostate.
Creatine
Phosphokinase (CPK or CK):
CPK catalyzes the reversible
transfer of phosphate groups between creatine and phosphocreatine as well as
between ATP and ADP. Most of the CPK resides in skeletal muscle, heart muscle,
and in the gastrointestinal tract. CPK enters the blood rapidly following
damage to muscle cells. At first CPK seemed to be an excellent marker for acute
myocardial infarction (heart damage) or skeletal muscle damage. Unfortunately, the
CPK levels rise and fall rapidly and coincide with a variety of other
circumstances including surgical procedures, vigorous exercise, a fall, or a
deep intramuscular injection. The measurement of CPK levels still provides
valuable differentiating diagnostic information.
Gamma-glutamyl Transpeptidase (GGT):
GGT catalyzes the transfer of
the glutamyl groups among different polypeptides and amino acids. Clinically
significant GGT found in the blood comes from cells that line the biliary
tract. GGT levels rise. Dramatically with obstructive diseases of the biliary
tract and liver cancers. GGT is especially useful in assessing liver function
associated with alcohol - induced liver disease.
Lactic Dehydrogenase (LDH):
This enzyme catalyzes the reversible
reaction between pyruvic and lactic acids.
LDH is present in nearly all types of
metabolizing cells, but different cells have different forms of the enzyme
which can be distinguished. 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. The LDH
isoenzymes test assists in differentiating heart attack, anemia, lung injury,
or liver disease from other conditions that may cause the same symptomsLDH-1 is found mainly
in the heart. LDH-2 is primarily associated with the system in the body that
defends against infection. LDH-3 is found in the lungs and other tissues, LDH-4
in the kidney, placenta, and pancreas, and LDH-5 in liver and 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.
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.
Lipase:
Lipase is an enzyme secreted by
the pancreas into the duodenum. Damage to the pancreas as in acute pancreatitis
results in lipase in the blood from the secretory cells.
Transaminases (GOT and GPT):
Glutamic-Oxaloacetic Transaminase (GOT)
occurs in large concentrations in
the heart and liver with moderate amounts in skeletal muscle, kidneys, and
pancreas. GOT levels can be used to diagnose myocardial infarction within 10-48
hours. Other conditions with elevated GOT include arrhythmias and severe angina
of the heart, and liver damage.
Glutamic-Pyruvic Transaminase (GPT)
is found in significant quantities in
liver, kidney, and skeletal muscle, in decreasing order. When liver cells are
damaged, GOT and GPT levels rise especially early in the disease. In hepatitis,
transaminase levels rise several days before jaundice begins. The enzyme levels
are especially useful in assessing subtle and early changes in biliary
obstruction and active cirrhosis.
