Cardiac Marker:- Part 3 – Troponins, Troponin-T, and Troponin-I
- It is done on the EDTA blood.
- This test can also be done in the serum or plasma.
- A serial sample may be needed.
- The serum for troponin-T is stable for 24 hours at 2 to 8 °C.
- Can store serum for three months at -20 °C.
- This test is advised to rule out myocardial infarction (MI) in a patient with chest pain.
- This is a specific indicator of cardiac damage or infarction.
- This is helpful to diagnose MI at an early stage.
- This test is done for the early diagnosis of myocardial infarction.
- Troponins are proteins present in the skeletal and cardiac muscles.
- Troponins have three subunits complex:
- It will regulate the interaction of actin and myosin.
- These reactions of actin and myosin regulate cardiac contraction.
- These are regulatory proteins.
- Troponin is a complex of :
- Troponin-C is a Ca-binding component.
- Troponin-I is an inhibitory component.
- Troponin-T is a tropomyosin-binding component.
- Troponins are present in myofibrils around 94% to 97%.
- Troponin cytoplasmic fraction is 3% to 6%.
Troponins and muscle injury
- 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.
- Troponin-T has no cross-reactivity with skeletal muscle, so this assay is 100 % specific for cardiac disease.
- Troponins help in the contraction of muscles, which is calcium-dependent, and there is the interaction of myosin and actin.
- There are two cardiac troponins :
- These are highly specific for cardiac muscle injury.
- Their role is just like CK-MB.
- Troponins are more specific than CK-MB.
- Troponins will be nearly normal or slightly raised in noncardiac muscle injuries.
- Troponins are measured by:
- Monoclonal antibody immunoassay.
- Enzyme-linked immunoassay.
- 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|
|Duration||Raised for a longer time||raised for a shorter time|
|Sensitivity||More sensitive||Less sensitive|
Advantage of Troponin over CK-MB:
||Increased in skeletal muscle injury, brain, lung, and renal failure|
|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|
- Cardiac Troponin-T = < 0.2 ng/mL
- Cardiac Troponin-I = < 0.03 mg/mL
- Troponin-T = 0 to 0.1 µg/L
- Troponin-I = <3.1 µg/L
- 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:
- Raised even in the first 3 hours.
- The peak level is 12 to 48 hours.
- Remain elevated up to 10 to 14 days.
Universal definition of acute myocardial infarction:
- Troponin value at least one of these is >99% of the normal.
- The rapid rise in CK-MB and falls to normal.
- Evidence of the ischemia.
- Prominent Q-wave.
- Elevation of ST-segment.
Positive or raised Troponin–I level seen in:
- Myocardial injury during surgery.
- In small myocardial infarcts, and can be detected for up to 7 to 10 days.
Positive or raised Troponin-T level was seen in:
- Acute myocardial infarction.
- Pre-Surgical myocardial infarction.
- Unstable angina.
- Non-ischemic diseases of the heart:
- Acute trauma involving muscles.
- Chronic renal failure.
- Heart failure.
- Pulmonary embolism.
- Renal insufficiency.
|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|