Review Metabolism
Energy Summary Glycolysis & Citric Cycle  Elmhurst College
Serum Enzymes Lipid Metabolism  Chemistry Department
Alcohol Metab. Effects   Protein Metabolism  Virtual ChemBook

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Diagnostic Serum Enzymes


Certain tissue cells contain characteristic enzymes which enter the blood only when the cells to which they are confined are damaged or destroyed. The presence in the blood of significant quantities of these specific enzymes indicates the probable site of tissue damage. Figure 9 gives a listing of a few enzymes of diagnostic importance and their relationship to the overall metabolic scheme.

Link to GPNotebook: Diagnostic Enzymes -


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.

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Lactic Dehydrogenase (LDH):

This enzyme catalyzes the reversible reaction between pyruvic and lactic acids.

Link to Chime: LDH -

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 symptoms.

LDH-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.


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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.