W18 - Enzymes and cardiac enzymes Flashcards
What is an enzyme?
A substance, usually a protein, that increases the rate of a chemical rxn without itself being changed in the overall process
a rxn catalysed by an enzyme is much quicker than an uncatalysed rxn - true or false?
true!
What is Km (Michaelis-Menton Constant)?
Km is the substrate concentration at which the reaction velocity is 50% of the maximum
high Km indicates ______ binding
high Km indicates weak binding
ALP is found in 4 organs - name them
- Intra- and extra-hepatic bile ducts
- Bone
- Intestines
- Placenta
Give 7 bone diseases in which ALP is raised
- Fracture
- Paget’s disease
- Osteomalacia
- Rickets
- Cancer (primary or metastasis)
- Primary hyperparathyroidism with bone involvement
- Renal osteodystrophy
Give 2 situations where it’s normal for ALP to be elevated
- Last trimester of pregnancy
- Childhood
(therefore there are age-specific reference ranges)
Give 2 placental conditions in which ALP is raised
- Pregnancy (last trimester)
- Germ cell tumours
Give hepatic conditions in which ALP is raised
usually due to intra- or extra-hepatic cholestatic liver disease (obstructive causes!)
Where is ALT found? What is it a marker of? What to consider if elevated?
ALT = Liver, kidney, pancreatitis, MI
BUT ONLY used as a marker for LIVER
If elevated, consider:
- Hepatitis (viral, alcohol)
- NAFLD
- Liver ischaemia
- Paracetamol OD
A 40 year old man presents with abdo main. The serum ALT is elevated. What tissue is the ALT most likely coming from?
Liver
Where is gamma-glutamyl transferase (GGT) found? What is it a marker of? What to consider if elevated?
Liver, biliary system, pancreas, kidneys
If elevated, consider:
- hepatobiliary disease => hepatitis, ALCOHOLIC liver disease, cholestatic liver disease
- Enzyme induction => ALCOHOLICS (w/ or without liver disease), rifampicin, phenytoin, phenobarbitone
- Pancreas => pancreatitis (but serum amylase is a better marker)
- Kidney => other biomarkers (creatinine, eGFR) much better
LDH has ___ monomers, named
LDH has 2 monomers, named M and H
What does elevated LDH signifiy?
- WBC =>
- RBC =>
- Placenta =>
- Skeletal muslce =>
- Liver injury =>
- Cardiac =>
Organ based:
- WBC => lymphoma
- RBC => haemolysis
- Placenta => Germ cell testicular cancer (seminoma)
- Skeletal muslce => myositis
- Liver injury => hepatic disease but better biomarkers are available
- Cardiac => better markers available
- it’s usually used to check how patients with lymphoma or germ cell testicular cancer are responding to treatment
Serum amylase is found in 2 organs - name them
- Exocrine pancreas
- Salivary glands
What could elevated serum amylase signify?
- Pancreas => acute pancreatitis, perforated duodenal ulcer, bowel obstruction (2ndary to injury to pancreas)
- Salivary gland => stones, infection (i.e. mumps)
**serum amylase will be elevated in 2 but not as high as pancreatitis
Creatine kinase is found in 2 tissues - name them
- Cardiac muscle
- Skeletal muscle
Elevated creatine kinase - name causes.
Skeletal muscle injury = rhabdomyolysis (MOST COMMON CAUSE), myositis, polymyosiitis, dermatomyosiitis, severe exercise, myopathy (Deuchene muscular dystrophy, statin use)
cardiac muscle injury = not used for this purpose as troponin is more sensitive
How many types of troponin do we have? Where are they found? Which is measured for cardiac injury?
3 - Troponin I, T, and C
CARDIAC and SKELETAL MYOCYTES
usually troponin I is the high-sensitivity cardiac troponin
Troponin I can be elevated in both _____ and ______ cardiac injury
Troponin I can be elevated in both primary and secondary cardiac injury
Name primary cardiac injuries (4) causing elevated troponin I
- Acute coronary syndrome (STEMI, NSTEMI, unstable angina)
- Myocarditis
- Cardiomyopathy (HOCM, dilated, restrictive, Arrhythmogenic right ventricular dysplasia)
- Aortic dissection
Name 4 factors affecting troponin results
- Age
- Gender (M>F usually)
- Acute/chronic kidney disease (role in clearance of troponin)
- Time of test
Troponin I from onset of chest pain:
- when does it peak?
- when does it return to normal?
Troponin I from onset of chest pain:
- when does it peak? roughly 8 hours later
- when does it return to normal? roughly 6-10 days later
If patient comes in with chest pain and it’s decided to check troponin I levels - when should they be checked? How are results interpreted?
- Take troponin I on admission
- Take 2nd troponin I 3 hours later
- if there is a 50% increase (even if within the reference range) that is suggestive of cardiac myocyte injury
