Serum Enzyme Tests

Question 1

What are the two categories that can cause elevated enzyme activity levels in the serum?

Answer 1

1. Generalized damage to hepatocytes

2. Cholestasis

Question 2

Any condition in which the flow of bile from the liver is inhibited or blocked.

Answer 2

Cholestasis

Question 3

Name some examples of extrahepatic cholestasis.

Answer 3

Occurs outside the liver

• Strictures
• Stones
• Pancreatitis
• Primary sclerosing cholangitis
• Cysts
• Tumors

Question 4

Name some examples of intrahepatic cholestasis.

Answer 4

Occurs inside the liver

• Alcoholic liver disease
• Primary biliary cirrhosis
• Viral hepatitis

Question 5

Name some medications that can cause cholestasis.

Answer 5

Antibiotics (penicillins), anabolic steroids, birth control pills

Question 6

Another abbreviation for AST

Answer 6

SGOT

Question 7

Another abbreviation for ALT

Answer 7

SGPT

Question 8

What do AST and ALT do?

Answer 8

They catabolize glycogenic amino acids

Question 9

What are the two isoforms of AST?

Answer 9

GOT1 = cytoplasmic form 
GOT2 = mitochondrial form

Question 10

What cofactor does both AST and ALT require?

Answer 10

Pyridoxal phosphate (PLP)

Question 11

How does the distribution of AST and ALT differ?

Answer 11

AST has broad tissue distribution = liver, cardiac muscle, skeletal muscle, kidney, brain, pancreas, lung, leukocytes, erythrocytes

ALT is predominantly found in the liver

Question 12

Which isoform of AST is the predominant form in the liver?

Answer 12

GOT2 mitochondrial form

Question 13

Where is ALT present?

Answer 13

Only in the cytoplasm

Question 14

What enzyme test is more specific for acute hepatocellular damage?

Answer 14

ALT is more specific than AST

Question 15

Are elevated AST and ALT specific for hepatobiliary disorders?

Answer 15

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

Question 16

AST > ALT

Answer 16

alcoholic hepatitis

Question 17

ALT > AST

Answer 17

viral hepatitis

Question 18

What does alkaline phosphatase do?

Answer 18

It is a membrane-bound metalloenzyme that catalyzes the hydrolysis of phosphomonoesters at an alkaline pH

Question 19

How many isoenzymes of ALP have been identified in humans?

Answer 19

Non-specific liver/bone/kidney
Intestinal
Placental
Germ-cell

Question 20

When will you find an elevated ALP?

Answer 20

With disorders of bone characterized by increased osteoblastic activity
During growth and pregnancy

Question 21

What does 5’ nucleotidase do?

Answer 21

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

Question 22

Where is 5’ NT found?

Answer 22

Broad distribution = liver, intestines, brain, heart, blood vessels, pancreas

– Not elevated in bone disease or pregnancy

Question 23

Where is 5’NT found specifically in the liver?

Answer 23

It is associated with canalicular and sinusoidal plasma membranes

Question 24

What does GGT do?

Answer 24

It catalyzes the transfer of gamma-glutamyl group from gamma-glutamyl-containing peptides (glutathione) to other peptides, amino acids or water

Question 25

Where is GGT found?

Answer 25

In cell membranes/plasma membranes

Broad tissue distribution: liver, kidney, brain, heart, spleen, pancreas

Question 26

What are some things that can elevate GGT?

Answer 26

Diseases of liver, biliary tract and pancreas
Certain medications (barbiturates, anticonvulsants)
Alcohol abuse