Biochemistry of chest pains Flashcards
Which tests are ordered when a patient presents with chest pains?
Troponin
FBC
LFT
Glucose
Cholesterol
What are two ways to risk stratify patients with chest pain?
Perform a 12-lead ECG
Look at troponin levels
What is a 12-lead ECG the main diagnostic test for?
Main diagnostic test for acute MI
What are troponin levels the main primary tests for?
Look for damage to the myocytes
What is troponin?
Cardiac enzyme involved in cardiac contraction
Released by the cardiac myocytes into the circulation when damaged
What are the two forms of troponin subunits?
cTnI
cTnT
What is the normal concentration of cTnT and cTnI in healthy population?
Very small or undetectable quantities in the blood
What happens to the blood concentration of cTnT and cTnI in MI?
Concentration is proportional to the level of damage to the heart
Causes detectable increase in cTnI and cTnT 3-6 hours after the onset of chest pain
Reaching a peak 8-28 hours
Remains elevated 3-10 days
What are the advantages of measuring troponin?
cTnI and cTnT are more sensitive and specific for heart injury that other markers like creatine kinase-MB or myoglobin
Remain elevated for longer periods of time
What sample is used to measure cardiac troponin levels?
Sample: serum or plasma
Collected by venipuncture in either
- a serum separating tube - gold top
- heparin vacutainer - green-top
What type of test is used to measure troponin levels?
High sensitivity troponin-T assays can detect raised levels 3 hours after the onset of chest pains
How is the blood sample sent from the A&E to Clinical Biochemistry?
By air-tube system
Marked urgent
What lab analyses troponin levels in blood or plasma?
Clinical Biochemistry
What is the turnover time for measuring troponin levels?
1 hour
What machine measures cardiac troponin?
Automated analyser
Machine with immunoassays
Uses chemiluminescence and magnetism to measure the concentrations of different proteins and molecules
What is CMIA?
Chemiluminescent Magnetic Immunoassay
Uses antibodies to bind to molecules and measures the light emitted from them
How does a CMIA measure troponin levels?
An immune complex sandwich is made from two types of cTnT antibody complexes, using cTnT protein from the sample as the filling
50 microlitres of the serum/ plasma sample is incubated with
- biotinylated cTnT antibody
- cTnT antibody labelled with a ruthenium complex
Streptavidin-coated magnetic microparticles are added, which bind the sandwich complex via the interaction between the biotinylated-cTnT and streptavidin
The mixture is transferred to the measuring cell, where the microparticles are magnetically captured onto the surface of an electrode
Unbound substances are washed away with a buffer solution
Application of voltage through the electrode generates an unstable excited electron state in the ruthenium complex
Upon relaxation to the lower-level state photons are released
The amount of light generated is proportional to the amount of cTnT in the sample
The amount of light measured by a photomultiplier, and from this the instrument calculates the troponin concentration using a calibration curve
What is the peak time where there is the highest troponin levels?
6-8 hours
When is troponin-T chronically elevated?
Patients with renal or heart failure
What is the first step to diagnosis when patients present to the A&E with chest pain?
Careful clinical history
Examination
ECG
Chest X-ray
Investigations to diagnose other causes of chest pain and evaluate clinical likelihood of evolving ACS
What happens if the troponin levels are negative whilst having clinical presentations of MI?
Repeat troponin test
3 hours after presentation and at least 6 hours after the onset of symptoms
What characterises a positive result of troponin levels the second time troponin levels are measured?
> 50% increase in troponin concentration
Does one positive measurement at the start of clinical presentation conclude acute MI?
No
Repeat troponin to evaluate cause of troponin elevation 6 hours after presentation
If there is not change in troponin levels = not early MI (late MI or other causes of chronic troponin elevation)
If there is a significant change in troponin level then MI is likely
What are the next steps following MI diagnosis?
Look for definitive treatment - angiogram
ROMANCE
Reduce risk factors - secondary prevention
- lowering cholesterol
- start on beta blocker
- lower weight
