Chemical Pathology 15 - Enzymes and cardiac markers Flashcards
(28 cards)
What is the Km?
[substrate] at which reaction velocity = 50% max
how does Km impact affinity?
high Km = weak affinity
low Km = strong affinity
What tumour marker can be used for germ cell, ovarian and testicular malignancies?
ALP
When is ALP elevated physiologically?
pregnancy (3rd trimester)
childhood (↑ALP at birth - bone growth → plateaus until just before puberty → ↓ when bone growth ceases
How can you differentiate between liver and bone causes of high ALP?
↑ GGT
↑GGT + ALP = ALP from liver
normal GGT
check vit D
If vitamin D is normal → request serum electrophoresis for ALP isoenzymes
Recall 4 pathologies that can cause a raised ALP
BLIP
- Bone
- Intrahepatic/extrahepatic bile ducts
- Intestine
- Placenta (germ cell tumours)
Recall some bone causes of raised ALP
fracture (NOT in osteoporosis unless fracture)
cancer (primary/mets)
primary hyperparathyroidism with bone involvement
renal osteodystrophy
Paget’s disease
osteomalacia
Which LFT enzyme is most specific to liver pathology?
ALT
also in renal/pancreatitis/MI (but better biomarkers available)
What is a physiological cause of ↑ALT
vigorous exercise along with ↑AST
ALT vs AST
Both in many organs
ALT - predominantly liver
AST - many organs e.g. heart, liver, skeletal muscle or kidneys
Which organ is GGT found in?
hepatobiliary disease mainly
hepatitis
alcoholic liver disease
cholestatis liver disease
How can hepatic and biliary disease be best distinguished on the LFTs?
ALT:ALP ratio
If ALT much higher than ALP = hepatic
ALP>ALT = hepatic
GGT not very helpful
What enzyme is upregulated in response to enzyme induction?
↑release during normal cell turnover
alcohol (w/wo liver disease),
rifampicin
old anti-epileptic drugs (phenytoin, phenobarbitone),
How many isoenzymes of LDH exist?
5
Recall 3 things that a raised LDH may indicate
- Haemolytic anaemia
- Tumour marker (lymphoma, germ cell testicular Ca, seminoma)
- Myositis (rheum)
Which enzyme is markedly raised in acute pancreatitis?
Serum amylase
can also measure lipase (acute) or faecal elastase (chronic)
What is macro amylase?
amylase binds immunoglobulin → not cleared
often benign
request amylase electrophoresis if suspected
What are the two types of creatine kinase?
skeletal muscle (CK-MM)
cardiac muscle (CK-MB) - cardiac injury
What is the most likely cause of a raised CK-MM?
rhabdomyolysis
myositis
polymyositis
dermatomyositis
severe exercise
myopathy (DMD, statins)
In which population is CK physiologically slightly raised?
Afrocaribbean
Which prescription drug may be the cause of a raised CK-MM(MB1?)?
Statins (as they can cause myopathy)
Clinical syndromes of statin-related myopathy = myalgia → rhabdomyolysis (mostly, w/ simvastatin when co-prescribed other medications involved in CYP3A4 – i.e. clarithromycin)
Where is troponin found?
cardiac and skeletal myocytes - for muscle contraction
3 types (I,T,C) - labs only measure cardiac troponins I + T
Recall some causes of raised troponin
primary cardiac injury
- ACS (STEMI, NSTEMI, unstable angina)
- myocarditis
- cardiomyopathy
- aortic dissection
secondary cardiac injury
- PE
- systemic infection
When does troponin begin to rise following chest pain?
2-4 hours after CP
