enzymes and cardiac markers Flashcards
what is the Km?
Michaelis-Menten constant or Km = [substrate] at which the reaction velocity is 50% of the maximum.
what do different Km values mean?
high Km indicates weak binding
low Km indicates strong binding.
what is an isoenzymes?
type of an enzyme that is specific to a particular tissue
list 4 sources of ALP?
How to differentiate source?
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
why is ALP high at birth and in childhood?
bone growth
why is AST measurement often unhelpful?
can come from a few organs such as the heart, liver, skeletal muscle or kidneys
…obvi so can ALT but less so
what should you be thinking of in elevated ALT?
A raised ALT should make you suspicious of hepatic liver disease, such as hepatitis, ischaemic liver disease, paracetamol OD.
Which markers are useful for distinguishing between hepatic and biliary disease?
ALT:ALP ratio
list situatoins where ggt is elevated?
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)
LDH is elevated in which conditions? where is it released from?
Lymphoma - WBCs
Haemolysis - RBCs (haemolytic anaemia)
Germ-cell testicular cancer (seminoma) - placenta
Myositis - skeletal muscle
Hepatic disease - liver
cardiac - Better biomarkers available
5 isoenzymes
Elevated LDH in patients with _____ or _____ us associated with poor prognosis and is associated with ______
with lymphoma or a germ cell testicular cancer
associated with tumour bulk
how are the isoenzymes of LDH made up?
LDH has two monomers – M and H and combine in various proportions
where is amylase found?
the exocrine pancreas
salivary glands
what conditions does elevated amylase point to?
acute pancreatitis should be your first diagnosis,
less commonly in perforated Duodenal Ulcer and bowel obstruction.
saliva isoenzyme of amylase is raised. which condition can this point to?
MUMPS
elevated CK may be seen in which cases?
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
where can troponin 1 be found?
Located within cardiac and skeletal myocytes where it participates in muscle contraction
Hs cTnI
list some primary and secondary causes of elevated troponin 1?
Primary: Acute coronary syndrome (STEMI, NSTEMI, unstable angina) Myocarditis Cardiomyopathy Aortic dissection
Secondary:
Pulmonary embolism or PE
Systemic infection
what factors can affect troponin?
Factors affecting troponin result: Age, gender, acute or chronic kidney disease, Time of test..
men - higher levels
renal impairment - clear less of it
what do troponin levels look like post myocyte injury?
2-4 hours after chest pain, troponin I begins to rise,
it peaks 12 hours later and
returns to normal 5-10 days later
what do all cases of ACS require?
admission
A patient with cardiac sounding chest pain + ST elevation in any ECG leads needs …..?
Urgent cardiology review,
Likely patient needs coronary revascularization
A patient with cardiac sounding chest pain + abnormal ECG + elevated troponins is which condition?
what is abnormal ecg?
what counts as increased troponin?
NSTEMI
ecg; st depression, t inversion
troponin:
>ref range and/or
>50% change between results at T0 and 3 hours later
patient: cardiac sounding chest pain + normal ECG or ST depression or T wave inversion with normal troponins iis which diagnosis?
next step?
unstable angina
Urgent cardiology review,
inpatient review
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?
stable angina
senior review and probably discharge with outpatient cardiology
how would one investigate Pagets disease of bone? what would you see?
Tc bisphosphonate scan:
asymmetrical areas of high turnover
how would one investigate graves disease ? what would you see?
tc pertechnitate
hot nodule
how would one investigate prathyroid gland and heart for high turnover?
what will you see?
Tc sesta-mibi scan
in a myocardial infarction you will see an area where there is no uptake of MIBI
