Troponin-T, and Troponin-I

Sample

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

Indications for Troponin-T and Troponin-I

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 helps diagnose MI at an early stage.
4. This test is done for the early diagnosis of myocardial infarction.

Definition of troponins:

1. Troponins are contractile proteins found within muscle fibers that help regulate contractions.
2. There are three troponins that work as complex.
   1. Troponin-T = Tropomyosin-binding component.
   2. Troponin-I =  Inhibitory component.
   3. Troponin-C = Calcium-binding component.
3. During muscle necrosis, Troponin-T and Troponin-I are released into blood circulation.
4. Troponin-T and Troponin-I levels in the blood increase, indicating muscle necrosis.
5. Troponins are not raised in angina.

Pathophysiology of Troponin-T and Troponin-I

1. Troponins are proteins present in the skeletal and cardiac muscles.
2. Troponins have three subunits complex:
   1. It will regulate the interaction of actin and myosin.
   2. These reactions of actin and myosin regulate cardiac contraction.
3. These are regulatory proteins.
4. Troponin is a complex of :
   1. Troponin-C is a Ca-binding component.
      1. It is not advised in AMI because this is not specific for myocardial muscles.
   2. Troponin-I is an inhibitory component.
   3. Troponin-T is a tropomyosin-binding component.
5. Troponins are present in myofibrils around 94% to 97%.
   1. Troponin cytoplasmic fraction is 3% to 6%.

Troponins and muscle injury:

1. 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.
   1. Troponins remain in the blood circulation from 1 to 14 days after the onset of AMI.
2. Troponin-T has no cross-reactivity with skeletal muscle, so this assay is 100 % specific for cardiac disease.
3. Troponins help in the contraction of muscles, which is calcium-dependent, and there is the interaction of myosin and actin.
4. There are two cardiac troponins:
   1. Troponin-T.
   2. Troponin-I.
   3. These are highly specific for cardiac muscle injury.
5. Their role is just like CK-MB.
6. Troponins are more specific than CK-MB.
   1. Troponins will be nearly normal or slightly raised in noncardiac muscle injuries.
7. Advantages of troponins:
   1. There is a quick release of troponins after the cardiac muscle injury (necrosis).
   2. These are present for a longer period of time after the heart attack.
8. 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:

Characteristic feature	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 in 4 to 8 hours. It is  elevated longer than CK-MB	It rises early than Troponin Disappears early than troponins.
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 Troponin-T, and Troponin-I

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 infarction:

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

Troponins interpretations:

1. Raised Troponin-T level establishes the diagnosis of AMI; even ECG or CK-MB is non-diagnostic (<50% of the cases).
2. It indicates irreversible necrosis of the myocardial muscles.
3. Serial Troponin-T level normal rules out the possibility of myocardial necrosis (AMI).
4. Troponins have replaced the CK-MB as the gold standard, replacing late diagnosis of AMI with the raised level of LDH.
5. Troponin-T is as sensitive as CK-MB in the first 48 hours of the onset of AMI. It is >85% in concordance with CK-MB.
   1. Troponin-T sensitivity during 0 to 2 hours after the onset of chest pain = 33%
   2. Troponin-T sensitivity during 2 to 4 hours after the onset of chest pain = 50%.
   3. Troponin-T sensitivity during 4 to8 hours after the onset of chest pain = 75%.
   4. Troponin-T sensitivity after 8 hours of the onset of chest pain          = 100%.
6. Troponin-I is 13 times more abundant in the myocardium than CK-MB, providing
7. Troponin-I remained increased for <9 days, while Troponin-T for 14 days.
   1. Troponins are increased in <50% of patients with acute pericarditis.
   2. A level of troponins <0.5 ng/mL indicates no myocardial damage.
   3. >2.0 ng/mL indicates some myocardial necrosis.

Universal definition of acute myocardial infarction:

1. The Troponin value of at least one of these is >99% of the normal.
2. The rapid rise in CK-MB and falls to normal.
3. Evidence of the ischemia.
4. Prominent Q-wave.
5. Elevation of ST-segment.

Positive or raised Troponin-I level seen in:

1. Myocardial injury during surgery.
2. Small myocardial infarcts and can be detected for 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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