Chemical Pathology 15 - Enzymes and cardiac markers

Question 1

What is the Km?

Answer 1

Michaelis Mentin constant
= concentration of substrate at which the reaction velocity is 50% of maximum

Question 2

What tumour marker can be used for germ cell, ovarian and testicular malignancies?

Answer 2

AFP

Question 3

When is ALP elevated physiologically?

Answer 3

In pregnancy and childhood

Question 4

Recall 4 pathologies that can cause a raised ALP

How to distinguish between the diff sources of ALP?

Answer 4

1. Bile duct pathology (eg cholestatic liver disease)
2. Bone pathology (fracture/ metabolic bone disease)
3. Germ cell tumours
4. Intestinal pathology (but not routinely used for investigation of bowel disorders)

*To distinguish between the diff sources: can order bone specific ALP assay; OR can order gamma GT- which would rise in the case of liver source of ALP*

Question 5

Which LFT enzyme is most specific to liver pathology?

Answer 5

ALT

Question 6

How can hepatic and biliary disease be best distinguished on the LFTs?

Answer 6

ALT:ALP ratio
If ALT much higher than ALP = hepatic

Question 7

How many isoenzymes of LDH exist?

Answer 7

5

Question 8

Recall 3 things that a raised LDH may indicate

Answer 8

1. Haemolytic anaemia
2. Tumour marker (lymphoma, germ cell testicular Ca)
3. Myositis (rheum)

Question 9

Which enzyme is markedly raised in acute pancreatitis?

Answer 9

Serum amylase

Question 10

What is the most likely cause of a raised CK-MB1?

Answer 10

Rhabdomyolysis (history of long lie/ big fall?)

Question 11

Where is CK-MB1 vs CK-MB2 produced?

Answer 11

CK-MB1 - skeletal muscle
CK-MB2 - cardiac muscle

**you only have one heart but several muscles - but it’s actually the opposite of this!

Question 12

In which population is CK physiologically slightly raised?

Answer 12

Afrocaribbean

Question 13

Which prescription drug may be the cause of a raised CK-MB1?

Answer 13

Statins (as they can cause myopathy)

Question 14

When does troponin I peak following chest pain?

Answer 14

2-4 hours

Question 15

Within what time period does troponin I return to normal following a cardiac event?

Answer 15

5-10 days

**this means it is not a good marker of re-infarction

Question 16

What change in troponin levels is indicative of cardiac myocyte injury?

Answer 16

A 50% increase or decrease between 2 measurements

Question 17

When is amylase level high?

Answer 17

Usually after acute pancreatitis

*usually 10x the upper limit of normal*

Question 18

What other nonspecific conditions can cause a ise in amylase?

Answer 18

renal insufficiency

intestinal infract/peirtonitis

cholecytsitis

salpingitis

ectopic pregnancy

Question 19

What does lipase >3 upper reference range indicate?

Answer 19

acute pancreatitis

Question 20

Which is the most specific marker of acute pancreatitis?

Answer 20

Serum LIPASE

Question 21

What is creatine kinase a marker of?

Answer 21

Muscle damage

Question 22

What are the two types of creatine kinase?

Answer 22

CK-MM: skeletal muscle

CK-MB (1 and 2): cardiac muscle

Question 23

What causes high creatine kinase?

Answer 23

Physiological: Afro-Caribbean (<5x upper limit of normal)
• Pathological: Duchenne Muscular Dystrophy (>10xULN), MI (>10xULN), Rhabdomyolysis,
Statin related myopathy (spectrum of myalgia to rhabdomyolysis occurring secondary to taking statins. RF: high dose, genetic predisposition, previous history of myopathy with another statin. Causes rise in CK. Reversible with cessation of statin).

Question 24

What is BNP?

Answer 24

Question 25

What is a more sensitive marker than BNP?

Answer 25

NT-proBNP

Question 26

What isoform of troponin is a marker of cardiac injury?

Answer 26

Troponin I/T

Question 27

When do you measure troponin following an MI?

Answer 27

At 6 hours and 12 hours opst onset of the pain

*100% sensitive and 98% specific at 12-24 hours*

Question 28

How long does troponin remain elevated for?

Answer 28

3-10 days

Question 29

When else can troponin be raised?

Answer 29

Coronary spasm

Coronary dissection

PCI

myocarditis

HF

cardiomyopathies

Sepsis

Cardiac surgery

Chest trauma

Defibrillation

Question 30

What is an international unit?

Answer 30

In chemical pathology, the term “international unit” or IU is used to show the concentration of an enzyme e.g. the upper limit of normal for ALT is 40IU/litre.
Put simply: 1 international unit is the quantity of enzyme that catalyses 1uMol of substrate in a minute (at a given temp and pH)
It is a measure of enzyme activity not mass or concentration

Question 31

How to measure re-infarction?

Answer 31

measure CK-MB

*better than troponin I because troponin I stays elevated for 10 days following an acute event*

Question 32

Troponin I vs T

Answer 32

Troponin I is more specific and sensitive

**I am the best**