Cardiac Marker – Part 3 – Troponins, Troponin-T, Troponin-I and Acute Myocardial Infarction

Sample

1. It is done on the EDTA blood.
2. This test can also be done on serum or plasma.
3. The serial sample may be needed.
4. The serum for troponin-T is stable for 24 hours at 2 to 8 °C.
   • For 3 months at -20 °C.

Indications

1. This test is advised to rule out myocardial infarction (MI) in a patient with chest pain.
2. This is a specific indicator of cardiac damage or infarction.
3. This is helpful to diagnose MI at an early stage.
4. This test is done for the early diagnosis of myocardial infarction.

Pathophysiology

1. Troponins are proteins present in the skeletal and cardiac muscles.
2. These are regulatory proteins.
3. Troponin is a complex of :
   1. Troponin-C is a Ca-binding component.
   2. Troponin-I is an inhibitory component.
   3. Troponin-T is a tropomyosin-binding component.
4. Troponins are present in myofibrils around 94 to 97%.
   1. Troponin cytoplasmic fraction is 3 to 6%.

Troponins and muscle injury

5. There are kits for Troponin-I, but because of its three forms in circulation and their variation in concentration, different assays don’t produce reproducible results.
6. Troponin-T has no cross-reactivity with skeletal muscle, so this assay is 100 % specific for cardiac disease.
7. Troponins help in the contraction of muscles, which is calcium-dependent, and there is the interaction of myosin and actin.
8. There are two cardiac troponins :
   1. Troponin-T.
   2. Troponin-I.
   3. These are highly specific for cardiac muscle injury.
9. Their role is just like CK-MB.
10. Troponins are more specific than CK-MB.
    1. Troponins will be nearly normal or slightly raised in non-cardiac muscle injuries.
11. Troponins are measured by:
    1. Monoclonal antibody immunoassay.
    2. Enzyme-linked immunoassay.
    3. Monoclonal sandwich antibody qualitative technique.

Troponin and CK-MB difference:

causative reason	Troponin T	CK-MB
Skeletal muscle injury	Normal	Raised
Brain / Lung injury	Normal	Raised
Cardiac injury	Raised	Raised
Duration	Raised for a longer time	raised for a shorter time
Sensitivity	More sensitive	Less sensitive

Advantage of Troponin over CK-MB:

	Troponins	CK-MB
Specificity	More specifically, for cardiac muscle injury. Normal in noncardiac muscle injury	Increased in skeletal muscle injury, brain, lung, and renal failure
Increased level	Increased early and remains elevated longer than CK-MB
Sensitivity	More sensitive to cardiac muscle injury than CK-MB	Less sensitive to cardiac muscle injury
Importance	More important for the evaluation of chest pain	Less important for the evaluation of chest pain

Normal

Source 1

• Cardiac Troponin-T = < 0.2 ng/mL
• Cardiac Troponin-I = < 0.03 mg/mL

Source 2

• Troponin-T = 0 to 0.1 µg/L
• TRoponin-I = <3.1 µg/L

Source 3

• Troponin I = <0.35 ng/mL
  • Or <0.35 µg/L
• Troponin T = <0.2 ng/mL
  • Or <0.2 µg/L

The pattern of Troponin-T in acute myocardial infaction:

1. Raised even in the first 3 hours.
2. The peak level is 12 to 48 hours.
3. Remain elevated up to 10 to 14 days.

 

The pattern of Troponin-I in acute myocardial infaction:

1. Raised in the first 4 to 8 hours.
2. Peal level is around 12 hours.
3. Remains elevated 7 to 10 days.

Universal definition of the acute myocardial infarction:

1. Troponin value at least one of these is >99% of the normal.
2. Evidence of the ischemia:

Positive or raised Troponin–I level seen in:

1. Myocardial injury during surgery.
2. In small myocardial infarcts, and can be detected up to 7 to 10 days.

Positive or raised Troponin-T level was seen in:

1. Acute myocardial infarction.
2. Pre Surgical myocardial infarction.
3. Unstable angina.
4. Non-ischemic diseases of the heart:
   1. Acute trauma involving muscles.
   2. Rhabdomyolysis.
   3. Polymyositis.
   4. Dermatomyositis.
   5. Chronic renal failure.
   6. Myocarditis.
   7. Pericarditis.
   8. Heart failure.
   9. Pulmonary embolism.
   10. Sepsis.
   11. Shock.
   12. Renal insufficiency.

Cardiac markers:

Marker	Detectable	Peak level	Return to normal
Troponin-T	4 to 8 hours	12 to 48 hours	7 to 10 days
Troponin- I	4 to 6 hours	12 hours	3 to 10 days
CK-MB	4 to 8 hours	12 to 24 hours	72 to 96 hours
LDH	2 to 5 days		10 days

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