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Flashcards in Biochemistry of chest pains Deck (24)
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1
Q

Which tests are ordered when a patient presents with chest pains?

A

Troponin

FBC

LFT

Glucose

Cholesterol

2
Q

What are two ways to risk stratify patients with chest pain?

A

Perform a 12-lead ECG

Look at troponin levels

3
Q

What is a 12-lead ECG the main diagnostic test for?

A

Main diagnostic test for acute MI

4
Q

What are troponin levels the main primary tests for?

A

Look for damage to the myocytes

5
Q

What is troponin?

A

Cardiac enzyme involved in cardiac contraction

Released by the cardiac myocytes into the circulation when damaged

6
Q

What are the two forms of troponin subunits?

A

cTnI

cTnT

7
Q

What is the normal concentration of cTnT and cTnI in healthy population?

A

Very small or undetectable quantities in the blood

8
Q

What happens to the blood concentration of cTnT and cTnI in MI?

A

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

9
Q

What are the advantages of measuring troponin?

A

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

10
Q

What sample is used to measure cardiac troponin levels?

A

Sample: serum or plasma

Collected by venipuncture in either

  • a serum separating tube - gold top
  • heparin vacutainer - green-top
11
Q

What type of test is used to measure troponin levels?

A

High sensitivity troponin-T assays can detect raised levels 3 hours after the onset of chest pains

12
Q

How is the blood sample sent from the A&E to Clinical Biochemistry?

A

By air-tube system

Marked urgent

13
Q

What lab analyses troponin levels in blood or plasma?

A

Clinical Biochemistry

14
Q

What is the turnover time for measuring troponin levels?

A

1 hour

15
Q

What machine measures cardiac troponin?

A

Automated analyser

Machine with immunoassays

Uses chemiluminescence and magnetism to measure the concentrations of different proteins and molecules

16
Q

What is CMIA?

A

Chemiluminescent Magnetic Immunoassay

Uses antibodies to bind to molecules and measures the light emitted from them

17
Q

How does a CMIA measure troponin levels?

A

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

18
Q

What is the peak time where there is the highest troponin levels?

A

6-8 hours

19
Q

When is troponin-T chronically elevated?

A

Patients with renal or heart failure

20
Q

What is the first step to diagnosis when patients present to the A&E with chest pain?

A

Careful clinical history

Examination

ECG

Chest X-ray

Investigations to diagnose other causes of chest pain and evaluate clinical likelihood of evolving ACS

21
Q

What happens if the troponin levels are negative whilst having clinical presentations of MI?

A

Repeat troponin test

3 hours after presentation and at least 6 hours after the onset of symptoms

22
Q

What characterises a positive result of troponin levels the second time troponin levels are measured?

A

> 50% increase in troponin concentration

23
Q

Does one positive measurement at the start of clinical presentation conclude acute MI?

A

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

24
Q

What are the next steps following MI diagnosis?

A

Look for definitive treatment - angiogram

ROMANCE

Reduce risk factors - secondary prevention

  • lowering cholesterol
  • start on beta blocker
  • lower weight