Serum Enzyme Tests Flashcards
What are the two categories that can cause elevated enzyme activity levels in the serum?
- Generalized damage to hepatocytes
2. Cholestasis
Any condition in which the flow of bile from the liver is inhibited or blocked.
Cholestasis
Name some examples of extrahepatic cholestasis.
Occurs outside the liver
- Strictures
- Stones
- Pancreatitis
- Primary sclerosing cholangitis
- Cysts
- Tumors
Name some examples of intrahepatic cholestasis.
Occurs inside the liver
- Alcoholic liver disease
- Primary biliary cirrhosis
- Viral hepatitis
Name some medications that can cause cholestasis.
Antibiotics (penicillins), anabolic steroids, birth control pills
Another abbreviation for AST
SGOT
Another abbreviation for ALT
SGPT
What do AST and ALT do?
They catabolize glycogenic amino acids
What are the two isoforms of AST?
GOT1 = cytoplasmic form GOT2 = mitochondrial form
What cofactor does both AST and ALT require?
Pyridoxal phosphate (PLP)
How does the distribution of AST and ALT differ?
AST has broad tissue distribution = liver, cardiac muscle, skeletal muscle, kidney, brain, pancreas, lung, leukocytes, erythrocytes
ALT is predominantly found in the liver
Which isoform of AST is the predominant form in the liver?
GOT2 mitochondrial form
Where is ALT present?
Only in the cytoplasm
What enzyme test is more specific for acute hepatocellular damage?
ALT is more specific than AST
Are elevated AST and ALT specific for hepatobiliary disorders?
No – this finding can be found in patients with severe cardiac and skeletal muscle damage
AST is more often increased in patients with myocardial infarction than ALT
AST > ALT
alcoholic hepatitis
ALT > AST
viral hepatitis
What does alkaline phosphatase do?
It is a membrane-bound metalloenzyme that catalyzes the hydrolysis of phosphomonoesters at an alkaline pH
How many isoenzymes of ALP have been identified in humans?
Non-specific liver/bone/kidney
Intestinal
Placental
Germ-cell
When will you find an elevated ALP?
With disorders of bone characterized by increased osteoblastic activity
During growth and pregnancy
What does 5’ nucleotidase do?
It is involved in purine catabolism. It catalyzes the hydrolysis of nucleotides like adenosine 5’-phosphate in which the phosphate is attached to the 5 position of the pentose ring
Where is 5’ NT found?
Broad distribution = liver, intestines, brain, heart, blood vessels, pancreas
– Not elevated in bone disease or pregnancy
Where is 5’NT found specifically in the liver?
It is associated with canalicular and sinusoidal plasma membranes
What does GGT do?
It catalyzes the transfer of gamma-glutamyl group from gamma-glutamyl-containing peptides (glutathione) to other peptides, amino acids or water
Where is GGT found?
In cell membranes/plasma membranes
Broad tissue distribution: liver, kidney, brain, heart, spleen, pancreas
What are some things that can elevate GGT?
Diseases of liver, biliary tract and pancreas
Certain medications (barbiturates, anticonvulsants)
Alcohol abuse
