Clinical Enzymology Flashcards
What are the ranges of cellular injury? I
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
What are isozymes ?
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
What reaction does creatine kinase?
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
What are the creatine kinase isozymes? What are they used for?
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)
What CK is in the brain?
Brain has mainly CK-BB
sCK-BB is elevated after CNS damage
What enzyme CK is found in the heart?
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
What are the CK isozymes?
Skeletal muscle has 98% CK-MM and 2% CK-MB
sCK-MM is elevated in rhambdomyolosis or muscular dystrophy
How does hemolytic anemia be indicated with lactate dehydrogenase ?
Severity is measured by the increase of LDH in serum following RBC destruction
How is myocardial infarction indicated by LDH?
Leads to increase of heart LDH isozymes in serum which show a high LDH-1/LDH-2 ratio
What is lactate dehydrogenase?
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
Contrast the time frame for in serum fir MI markers
CK-MB level peaks after 24 hours.
LDH level peaks later after 48 hours
Myocardial infarction leads to increase in…
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
What are troponins?
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
What does myocardial infarction lead to?
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:
- Increase in cardiac troponins (cTnI or cTnT)
- Increase in CK-MB
What are the methods to determine MI injury markers?
Electrophoresis : different charge
RIA: Rafioimmunoassay
Elisa: Enzyme-linked immunosorbent assays are used to measure CK-MB, cTnI, cTnT and myoglobin
Aside from heart attacks, what do chest pains indicate?
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
What tests can be used to assess liver functions ?
- ammonium (high)
- albumin(reduced)
- bilirubin (high)
What tests can be used to ass liver membrane integrity?
Alanine aminotransferase (ALT)
Aspartate aminotransferase
How can ALT/AST indicate the source of liver damage?
- High ALT/AST ratio is characteristic for hepatic viral infection
- High AST/ALT ratio is characteristic for hepatic alcohol damage
What may cause bile obstruction?
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
What are the injury markers for obstructed bile ducts?
- 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
- 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
What is the cause of pancreatitis?
Acute due to:
-heavy alcohol intake (40%)
-Gallstone blockage (40%)
Chronic due to:
- Cystic fibrosis (CF)
- Hyperlipidemia
- Years of ethanol abuse
What can be used to indicate pancreatitis?
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
Where is alkaline phosphatase found? What does it do?
- 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
What does alkaline phosphatase indicate?
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
What test can be used to diagnose prostate cancer ?
Instead of test for acid phosphatase, use prostate specific antigen test
What specific serum marker can be used for liver cancer?
Alpha-fetoprotein (AFP): This protein is normally synthesized in the fetal liver (instead of albumin). In adults it can indicate liver cancer
