Clinical Enzymology

Question 1

What are the ranges of cellular injury? I

Answer 1

Increased enzyme levels

Mild: 2-3 times upper limits of normal

Moderate: 2-20 times

Marked: greater than 2 0 times

Enzyme increase In serum is used to diagnose

Question 2

What are isozymes ?

Answer 2

These catalyze the same biochemical reaction and they have multiple forms of the same enzyme

• They have different biochemical and immunological properties
• They often have a different amino acid sequence of different amino acid composition and can be separated by electrophoresis
• Different tissues frequently contain isozymes with different proportions of subunits. In case of cell damage, the resulting particular serum pattern can indicate the affected organ

Question 3

What reaction does creatine kinase?

Answer 3

Creatine kinase catalyzes a reversible reaction

At high ATP levels creative phosphate (CrP) is formed. At high CrP levels ATP is formed using the energy rich CrP

Creatine phosphate or phosphocreatine energy rich-molecule

Question 4

What are the creatine kinase isozymes? What are they used for?

Answer 4

CK in serum used as markers

CK contains the two subunits B and M which leads to 3 isozymes:

• CK-BB(CK-1)
• CK-MB(CK-2)
• CK-MM(CK-3)

Question 5

What CK is in the brain?

Answer 5

Brain has mainly CK-BB

sCK-BB is elevated after CNS damage

Question 6

What enzyme CK is found in the heart?

Answer 6

Heart muscle has the highest % of CK-MB: 30% CK-MB and 70% CK-MM

sCK-MB and sCK-MM are elevated after myocardial infarction

Question 7

What are the CK isozymes?

Answer 7

Skeletal muscle has 98% CK-MM and 2% CK-MB

sCK-MM is elevated in rhambdomyolosis or muscular dystrophy

Question 8

How does hemolytic anemia be indicated with lactate dehydrogenase ?

Answer 8

Severity is measured by the increase of LDH in serum following RBC destruction

Question 9

How is myocardial infarction indicated by LDH?

Answer 9

Leads to increase of heart LDH isozymes in serum which show a high LDH-1/LDH-2 ratio

Question 10

What is lactate dehydrogenase?

Answer 10

A tetramer of H and M subunits

LDH-1(H4) present in heart and RBC(mostly heart)

LDH-2(H3,M1) present in heart and RBC (mostly RBC)

LDH-5 present in muscle and liver

Question 11

Contrast the time frame for in serum fir MI markers

Answer 11

CK-MB level peaks after 24 hours.

LDH level peaks later after 48 hours

Question 12

Myocardial infarction leads to increase in…

Answer 12

Total CK and CK-MB in serum

Serum CK was introduced in 1965 as a biochemical marker for myocardial damage. The total CK found in the serum after an MI contains mainly CK-MM but also the heart characteristic CK-MB

A high CK-MB/total CK ratio indicates a large area of damaged heart muscle.

Criteria for imdication of an MI:

a. The CK-MB/Total CK ratio is larger than 6%
b. The CK-MB/Total CK ratio is larger than 3% and troponin are increased

Question 13

What are troponins?

Answer 13

Troponins are proteins involved with muscle contraction

Specific troponin isoforms are measured as heart injury markers:

Cardiac troponin I (cTnI: Inhibition of actomyosin ATPase)

Cardiac troponin T (cTnT: Tropomyosin binding)

Note: Troponin C(calcium binding) doesn’t have a specific isoforms for the heart

Question 14

What does myocardial infarction lead to?

Answer 14

Leads to myocardial cell death and CK-MB and troponins accumulate in blood

Recommended by the European Society of Cardiology and the American college of Cardiology are the following biochemical markers for the diagnosis of an acute MI:

1. Increase in cardiac troponins (cTnI or cTnT)
2. Increase in CK-MB

Question 15

What are the methods to determine MI injury markers?

Answer 15

Electrophoresis : different charge

RIA: Rafioimmunoassay

Elisa: Enzyme-linked immunosorbent assays are used to measure CK-MB, cTnI, cTnT and myoglobin

Question 16

Aside from heart attacks, what do chest pains indicate?

Answer 16

Chest pains also occur in:

• Severe exercise
• Acid reflux
• Intestinal has

Cardiac troponins and CK-MB are measured: An increase or no increase in serum can indicate or rule out an MI in patients with current chest pain and inconclusive ECG

Question 17

What tests can be used to assess liver functions ?

Answer 17

• ammonium (high)
• albumin(reduced)
• bilirubin (high)

Question 18

What tests can be used to ass liver membrane integrity?

Answer 18

Alanine aminotransferase (ALT)

Aspartate aminotransferase

Question 19

How can ALT/AST indicate the source of liver damage?

Answer 19

1. High ALT/AST ratio is characteristic for hepatic viral infection
2. High AST/ALT ratio is characteristic for hepatic alcohol damage

Question 20

What may cause bile obstruction?

Answer 20

Extra-hepatic bile ducts are obstructed by:

• Gall stones (cholesterol gallstones)
• Tumors (tumor in head of pancreas)

Intra-hepatic bile ducts can be irritated in liver cirrhosis

Question 21

What are the injury markers for obstructed bile ducts?

Answer 21

1. Alkaline phosphatase (ALP) is found in high concentration in cells of the bile canaculi and biliary ducts. ALP cleaves phosphatase from nucleotides and proteins which leads to the alkaline pH of bile
2. y-glutamate transferase (GGT) is bound to the plasma membrane of hepatocytes and is part of the hepatic y-glutathione (GSH) synthesis.

GGT increase in serum indicates injury of bile ducts and of the liver. It can result from gallstones, ethanol or medical drugs

Question 22

What is the cause of pancreatitis?

Answer 22

Acute due to:
-heavy alcohol intake (40%)

-Gallstone blockage (40%)

Chronic due to:

• Cystic fibrosis (CF)
• Hyperlipidemia
• Years of ethanol abuse

Question 23

What can be used to indicate pancreatitis?

Answer 23

Acute pancreatitis is indicated by increased serum levels of a-amylase and pancreatic lipase

Ethanol: Serum lipase/amylase ratio greater than 2

Gallstone blockage: Increase of serum amylase, lipase, ALP and GGT

Chronic pancreatitis can show less enzyme increase in serum due to less synthesis inside the pancreas

Question 24

Where is alkaline phosphatase found? What does it do?

Answer 24

• ALPbin bones creates an alkaline pH fir calcium deposition onto collagen
• Natural rise of ALP occurs in serum during bone growth and healing of fractures and during pregnancy

Question 25

What does alkaline phosphatase indicate?

Answer 25

Abnormal increase in serum in Padgett disease or bone tumors

Note: high serum ALP is also found on bile duct obstruction but is then combined with high GGT

Question 26

What test can be used to diagnose prostate cancer ?

Answer 26

Instead of test for acid phosphatase, use prostate specific antigen test

Question 27

What specific serum marker can be used for liver cancer?

Answer 27

Alpha-fetoprotein (AFP): This protein is normally synthesized in the fetal liver (instead of albumin). In adults it can indicate liver cancer