enzymes and cardiac markers

Question 1

what is the Km?

Answer 1

Michaelis-Menten constant or Km = [substrate] at which the reaction velocity is 50% of the maximum.

Question 2

what do different Km values mean?

Answer 2

high Km indicates weak binding

low Km indicates strong binding.

Question 3

what is an isoenzymes?

Answer 3

type of an enzyme that is specific to a particular tissue

Question 4

list 4 sources of ALP?

How to differentiate source?

Answer 4

Intra and extrahepatic bile ducts

Bone

Placenta - high in last pregnancy semester, germ cell tumours

Intestines

dfx;
history, clinical picture, vitamin d, ggt
serum electrophoresis for the isoenzymes

Question 5

why is ALP high at birth and in childhood?

Answer 5

bone growth

Question 6

why is AST measurement often unhelpful?

Answer 6

can come from a few organs such as the heart, liver, skeletal muscle or kidneys

…obvi so can ALT but less so

Question 7

what should you be thinking of in elevated ALT?

Answer 7

A raised ALT should make you suspicious of hepatic liver disease, such as hepatitis, ischaemic liver disease, paracetamol OD.

Question 8

Which markers are useful for distinguishing between hepatic and biliary disease?

Answer 8

ALT:ALP ratio

Question 9

list situatoins where ggt is elevated?

Answer 9

γ-GT synthesis is upregulated in response to drugs such as alcohol (and patients may or may not have liver disease), rifampicin and old anti-epileptic drugs (phenytoin, phenobarbitone),

so more of the enzyme is released from the cell during normal cell turnover due to upregulation (/ enzyme induction by drugs)

Question 10

LDH is elevated in which conditions? where is it released from?

Answer 10

Lymphoma - WBCs
Haemolysis - RBCs (haemolytic anaemia)
Germ-cell testicular cancer (seminoma) - placenta

Myositis - skeletal muscle
Hepatic disease - liver
cardiac - Better biomarkers available

5 isoenzymes

Question 11

Elevated LDH in patients with _____ or _____ us associated with poor prognosis and is associated with ______

Answer 11

with lymphoma or a germ cell testicular cancer

associated with tumour bulk

Question 12

how are the isoenzymes of LDH made up?

Answer 12

LDH has two monomers – M and H and combine in various proportions

Question 13

where is amylase found?

Answer 13

the exocrine pancreas

salivary glands

Question 14

what conditions does elevated amylase point to?

Answer 14

acute pancreatitis should be your first diagnosis,

less commonly in perforated Duodenal Ulcer and bowel obstruction.

Question 15

saliva isoenzyme of amylase is raised. which condition can this point to?

Answer 15

MUMPS

Question 16

elevated CK may be seen in which cases?

Answer 16

Cardiac muscle:
Cardiac injury - not used for this purpose (high-sensitivity troponin is better and used instead).

Skeletal muscle:
Rhabdomyolysis,
Myositis, polymyositis, dermatomyositis,
Severe exercise,

Myopathy (Deuchene muscular dystrophy + Statins)

*slightly higher levels in individuals of Afro-Carribean descent

Question 17

where can troponin 1 be found?

Answer 17

Located within cardiac and skeletal myocytes where it participates in muscle contraction

Hs cTnI

Question 18

list some primary and secondary causes of elevated troponin 1?

Answer 18

Primary:
Acute coronary syndrome (STEMI, NSTEMI, unstable angina) 
Myocarditis 
Cardiomyopathy 
Aortic dissection 

Secondary:
Pulmonary embolism or PE
Systemic infection

Question 19

what factors can affect troponin?

Answer 19

Factors affecting troponin result: Age, gender, acute or chronic kidney disease, Time of test..

men - higher levels
renal impairment - clear less of it

Question 20

what do troponin levels look like post myocyte injury?

Answer 20

2-4 hours after chest pain, troponin I begins to rise,

it peaks 12 hours later and

returns to normal 5-10 days later

Question 21

what do all cases of ACS require?

Answer 21

admission

Question 22

A patient with cardiac sounding chest pain + ST elevation in any ECG leads needs …..?

Answer 22

Urgent cardiology review,

Likely patient needs coronary revascularization

Question 23

A patient with cardiac sounding chest pain + abnormal ECG + elevated troponins is which condition?

what is abnormal ecg?
what counts as increased troponin?

Answer 23

NSTEMI

ecg; st depression, t inversion

troponin:
>ref range and/or
>50% change between results at T0 and 3 hours later

Question 24

patient: cardiac sounding chest pain + normal ECG or ST depression or T wave inversion with normal troponins iis which diagnosis?

next step?

Answer 24

unstable angina

Urgent cardiology review,

inpatient review

Question 25

patient: Exertional chest pain relieved by rest or GTN + normal resting ECG + two troponin results that are within the reference range and there is not a 50% change in the results iis which diagnosis?

next step?

Answer 25

stable angina

senior review and probably discharge with outpatient cardiology

Question 26

how would one investigate Pagets disease of bone? what would you see?

Answer 26

Tc bisphosphonate scan:

asymmetrical areas of high turnover

Question 27

how would one investigate graves disease ? what would you see?

Answer 27

tc pertechnitate

hot nodule

Question 28

how would one investigate prathyroid gland and heart for high turnover?

what will you see?

Answer 28

Tc sesta-mibi scan

in a myocardial infarction you will see an area where there is no uptake of MIBI