Chem path 16 - Enzymes and cardiac markers

Question 1

Which type of enzyme is released first from a necrosed cell?

Answer 1

Cytosolic enzymes are released before subcellular enzyme

Question 2

In which two places can enzymes be measured?

Answer 2

In the serum (injury) and in the tissue (abnormalities)

Question 3

How can iso-enzymes be separated out?

Answer 3

Electrophoresis (isoenzymes have different Kms)

Question 4

What is Km (Michaelis-Menten constant)

Answer 4

=[substrate] at which reaction velocity is 50% of the maximum

Question 5

What do high and low Kms indicate?

Answer 5

High Km = weak binding

Low Km = strong binding

Question 6

Where is ALP found?

Answer 6

BLIP (bone liver intestines placenta)

Question 7

When is an elevated ALP physiological?

Answer 7

During pregnancy (third trimester) and childhood

Question 8

ALP is high in bone diseases associated with which type of activity?

Answer 8

Osteoblastic activity

Question 9

What is the clinical approach to unexplained ALP/

Answer 9

1. LFTs (GGT and ALT)
2. Check vitD
3. ALP isoenzymes - performed by electrophoresis test

Question 10

Which 3 ways can bone and liver ALP be differentiates?

Answer 10

GGT measurement
Electrophoresis separation
Bone ALP immunoassay

Question 11

Pathological causes of raised ALP <5x upper limit

Answer 11

Bone - tumours, fractures, osteomyelitis

Liver - Infiltrative disease, hepatitis

Question 12

Pathological causes of raised ALP >5x upper limit

Answer 12

Bone - Paget’s disease, osteomalacia

Liver - Cholestasis, cirrhosis

Question 13

Is ALT or AST more speciifc to the liver?

Answer 13

ALT

Question 14

What numerical cut off of ALT is highly suggestive of paracetamol OD?

Answer 14

ALT >1000 (ULN 45)

Question 15

In which conditions does an elevated LDH carry a poor prognosis?

Answer 15

Germ cell testicular cancer or lymphoma

Question 16

What is amylase a marker of?

Answer 16

Acute pancreatitis

Question 17

What else is often measured as a marker of acute pancreatitis?

Answer 17

Pancreatic lipase

Question 18

Which other gland produces an amylase isoenzyme?

Answer 18

Salivary glands - amylase can be raised in parotitis (mumps)

Question 19

What do you measure in chronic pancreatitis?

Answer 19

Foecal elastase

Question 20

What is a common SE of statins?

Answer 20

Statin-related myopathy

Question 21

Which creatine kinase isoenzyme can help make the diagnosis of statin-related myopathy?

Answer 21

CK-MM (>10X UL)

Question 22

What are the clinical syndromes of statin-related myopathy

Answer 22

Myalgia –> rhabdomyolysis

Question 23

Name some risk factors for statin-related myopathy

Answer 23

Polypharmacy (other drugs metabolised by CYP3A4 e.g. clarithromycin, fibrates, cyclosporin)
High doses
genetic predisposition
previous myopathy with statins  
vitamin D deficiency

Question 24

Other than statins, what are some other causes of raised CK?

Answer 24

MI, Myositis, myopathy e.g. Duchenne’s, severe exercise, physiological (AFC)

Question 25

Which enzyme MUST be measured before starting thiopurine drugs such as azathioprine

Answer 25

TPMT

Question 26

Which cardiac enzyme rises fastest folllowing MI and why?

Answer 26

Myoglobin (Cytosolic)

Question 27

Which is the best enzyme marker following MI?

Answer 27

Troponin

Question 28

Which enzyme is best to detect a re-infarction following an MI?

Answer 28

CK-MB

Question 29

What are the three types of troponin called?

Answer 29

I,T,C

Question 30

What is needed to make a diagnosis of MI?

Answer 30

History, exam, ECG, troponin

Question 31

Name 3 factors which affect troponin levels

Answer 31

Age, gender (Women have less), pts with renal impairment clear less troponin

Question 32

When do troponin levels rise, peak and fall?

Answer 32

Rise 4-6 hrs
Peak 12-24 hrs
Fall 3-10 days

Question 33

When should troponin levels be measured following MI?

Answer 33

First at 6 hours and again 12 hours after

Question 34

What are the sensitivities and specificities of troponin at 12 hours?

Answer 34

100% sensitive

98% specific

Question 35

What can be seen on the ECG of someone with MI?

Answer 35

Pathological Q waves

ST elevation

Question 36

Name 2 markers of heart failure

Answer 36

ANP (Atria)

BNP (ventricles)

Question 37

What is IU a measure of?

Answer 37

IU is a measure of enzyme mass/concentration NOT ACTIVITY

Question 38

What is one IU of enzyme activity equivalent to?

Answer 38

quantity of enzyme that catalyses 1 umol of substrate per minute