W18 - Enzymes and cardiac enzymes

Question 1

What is an enzyme?

Answer 1

A substance, usually a protein, that increases the rate of a chemical rxn without itself being changed in the overall process

Question 2

a rxn catalysed by an enzyme is much quicker than an uncatalysed rxn - true or false?

Answer 2

true!

Question 3

What is Km (Michaelis-Menton Constant)?

Answer 3

Km is the substrate concentration at which the reaction velocity is 50% of the maximum

Question 4

high Km indicates ______ binding

Answer 4

high Km indicates weak binding

Question 5

ALP is found in 4 organs - name them

Answer 5

1. Intra- and extra-hepatic bile ducts
2. Bone
3. Intestines
4. Placenta

Question 6

Give 7 bone diseases in which ALP is raised

Answer 6

1. Fracture
2. Paget’s disease
3. Osteomalacia
4. Rickets
5. Cancer (primary or metastasis)
6. Primary hyperparathyroidism with bone involvement
7. Renal osteodystrophy

Question 7

Give 2 situations where it’s normal for ALP to be elevated

Answer 7

1. Last trimester of pregnancy
2. Childhood

(therefore there are age-specific reference ranges)

Question 8

Give 2 placental conditions in which ALP is raised

Answer 8

1. Pregnancy (last trimester)
2. Germ cell tumours

Question 9

Give hepatic conditions in which ALP is raised

Answer 9

usually due to intra- or extra-hepatic cholestatic liver disease (obstructive causes!)

Question 10

Where is ALT found? What is it a marker of? What to consider if elevated?

Answer 10

ALT = Liver, kidney, pancreatitis, MI

BUT ONLY used as a marker for LIVER

If elevated, consider:

1. Hepatitis (viral, alcohol)
2. NAFLD
3. Liver ischaemia
4. Paracetamol OD

Question 11

A 40 year old man presents with abdo main. The serum ALT is elevated. What tissue is the ALT most likely coming from?

Answer 11

Liver

Question 12

Where is gamma-glutamyl transferase (GGT) found? What is it a marker of? What to consider if elevated?

Answer 12

Liver, biliary system, pancreas, kidneys

If elevated, consider:

• hepatobiliary disease => hepatitis, ALCOHOLIC liver disease, cholestatic liver disease
• Enzyme induction => ALCOHOLICS (w/ or without liver disease), rifampicin, phenytoin, phenobarbitone
• Pancreas => pancreatitis (but serum amylase is a better marker)
• Kidney => other biomarkers (creatinine, eGFR) much better

Question 13

LDH has ___ monomers, named

Answer 13

LDH has 2 monomers, named M and H

Question 14

What does elevated LDH signifiy?

• WBC =>
• RBC =>
• Placenta =>
• Skeletal muslce =>
• Liver injury =>
• Cardiac =>

Answer 14

Organ based:

• WBC => lymphoma
• RBC => haemolysis
• Placenta => Germ cell testicular cancer (seminoma)
• Skeletal muslce => myositis
• Liver injury => hepatic disease but better biomarkers are available
• Cardiac => better markers available
• it’s usually used to check how patients with lymphoma or germ cell testicular cancer are responding to treatment

Question 15

Serum amylase is found in 2 organs - name them

Answer 15

1. Exocrine pancreas
2. Salivary glands

Question 16

What could elevated serum amylase signify?

Answer 16

1. Pancreas => acute pancreatitis, perforated duodenal ulcer, bowel obstruction (2ndary to injury to pancreas)
2. Salivary gland => stones, infection (i.e. mumps)

**serum amylase will be elevated in 2 but not as high as pancreatitis

Question 17

Creatine kinase is found in 2 tissues - name them

Answer 17

1. Cardiac muscle
2. Skeletal muscle

Question 18

Elevated creatine kinase - name causes.

Answer 18

Skeletal muscle injury = rhabdomyolysis (MOST COMMON CAUSE), myositis, polymyosiitis, dermatomyosiitis, severe exercise, myopathy (Deuchene muscular dystrophy, statin use)

cardiac muscle injury = not used for this purpose as troponin is more sensitive

Question 19

How many types of troponin do we have? Where are they found? Which is measured for cardiac injury?

Answer 19

3 - Troponin I, T, and C

CARDIAC and SKELETAL MYOCYTES

usually troponin I is the high-sensitivity cardiac troponin

Question 20

Troponin I can be elevated in both _____ and ______ cardiac injury

Answer 20

Troponin I can be elevated in both primary and secondary cardiac injury

Question 21

Name primary cardiac injuries (4) causing elevated troponin I

Answer 21

1. Acute coronary syndrome (STEMI, NSTEMI, unstable angina)
2. Myocarditis
3. Cardiomyopathy (HOCM, dilated, restrictive, Arrhythmogenic right ventricular dysplasia)
4. Aortic dissection

Question 22

Name 4 factors affecting troponin results

Answer 22

1. Age
2. Gender (M>F usually)
3. Acute/chronic kidney disease (role in clearance of troponin)
4. Time of test

Question 23

Troponin I from onset of chest pain:

• when does it peak?
• when does it return to normal?

Answer 23

Troponin I from onset of chest pain:

• when does it peak? roughly 8 hours later
• when does it return to normal? roughly 6-10 days later

Question 24

If patient comes in with chest pain and it’s decided to check troponin I levels - when should they be checked? How are results interpreted?

Answer 24

1. Take troponin I on admission
2. Take 2nd troponin I 3 hours later
   - if there is a 50% increase (even if within the reference range) that is suggestive of cardiac myocyte injury