Unit Converter
Troponin I (TnI)
(Cardiac-Specific Regulatory Protein - Gold-Standard Biomarker for Myocardial Injury & Acute Myocardial Infarction)
Synonyms
- Troponin-I
- Cardiac troponin I (cTnI)
- High-sensitivity Troponin I (hs-TnI)
- TnI
- cTnI-hs
- hs-cTnI
Units of Measurement
- ng/mL
- ng/dL
- ng/100 mL
- ng%
- ng/L
- µg/L
Unit Conversions
ng/mL ↔ ng/L
1 ng/mL=1000 ng/L1\ \text{ng/mL} = 1000\ \text{ng/L}1 ng/mL=1000 ng/L
ng/mL ↔ µg/L
1 ng/mL=1 µg/L1\ \text{ng/mL} = 1\ \text{µg/L}1 ng/mL=1 µg/L
ng/dL = ng/100 mL = ng%
ng/L → ng/mL
1000 ng/L=1 ng/mL1000\ \text{ng/L} = 1\ \text{ng/mL}1000 ng/L=1 ng/mL
Description
Troponin I is a cardiac-specific regulatory protein located in the contractile apparatus of cardiomyocytes.
It is released into the bloodstream when cardiac muscle cells are injured.
Modern assays use high-sensitivity Troponin I (hs-TnI), capable of detecting extremely small amounts of myocardial injury.
Why Troponin I is important:
- Most specific marker for myocardial injury
- Detects acute myocardial infarction (AMI) early
- Helps diagnose unstable angina, NSTEMI, and STEMI
- Useful for prognosis in heart failure, CKD, sepsis, and tachyarrhythmias
Troponin I is more cardiac-specific than Troponin T.
Physiological Role
Troponin complex = TnC (calcium binding) + TnI (inhibitory) + TnT (tropomyosin binding)
TnI blocks actin–myosin interaction during muscle relaxation.
Only cardiac isoform (cTnI) leaks into blood when myocytes are damaged.
Clinical Significance
HIGH TROPONIN I
1. Acute Myocardial Infarction (AMI) - Primary Use
According to the Fourth Universal Definition of MI:
Troponin elevation above 99th percentile + a rise/fall pattern = MI (with clinical evidence).
Typical AMI pattern:
- Detectable at 2–3 hours
- Peak at 12–24 hours
- Remains elevated 7–10 days
2. Myocardial Injury
Troponin can rise without coronary occlusion.
Major causes:
- Sepsis
- Tachyarrhythmia
- Heart failure
- Myocarditis
- Pulmonary embolism
- Renal failure
- Stroke / SAH
- Severe anemia / hypoxia
- Hypertensive crisis
- Critically ill patients
3. Chronic Elevation
Seen in:
- CKD/ESRD
- Structural heart disease
- Elderly
- Cardiomyopathies
Interpretation requires evaluating delta change.
LOW / NORMAL TROPONIN
Normal TnI does not rule out:
- Very early MI (<1–2 hours)
- Unstable angina
Repeat testing is mandatory.
Reference Intervals (High-Sensitivity assays)
(Varies by manufacturer — based on ESC/ACC guidelines)
99th Percentile Upper Reference Limit (URL)
- Males: 34 ng/L
- Females: 16 ng/L
Typical Laboratory Cutoffs
- Normal: < 10 ng/L
- Borderline: 10–40 ng/L
- Definite myocardial injury: > 40 ng/L
Critical Values
- > 10,000 ng/L → large infarct / major myocardial necrosis
Diagnostic Uses
1. Diagnosis of AMI
- Rise/fall of troponin + symptoms/ECG/imaging
- Preferred at 0-1 hr or 0-3 hr ESC algorithms
2. Risk Stratification
Higher peaks predict:
- Mortality
- Heart failure
- Recurrent MI
3. Monitoring Myocardial Injury
- Myocarditis
- Pulmonary embolism
- Critical illness
4. Peri-procedural MI detection
- PCI-related MI
- CABG-related MI
5. Evaluation of Chest Pain in ED
Most common test in emergency medicine worldwide.
Analytical Notes
- hs-TnI assays detect Troponin I at femtogram–picogram range.
- Different manufacturers → different cutoffs; values not interchangeable.
- Hemolysis, heterophile antibodies may cause interference.
- Renal failure elevates baseline — look for rise/fall rather than single value.
- Sample: serum or plasma (heparin / EDTA).
Clinical Pearls
- Serial change (rise/fall) is more important than single value.
- Troponin elevation ≠ MI automatically - always correlate clinically.
- TnI has no skeletal muscle cross-reactivity, unlike CK-MB.
- High troponin in sepsis predicts higher mortality even without MI.
- A normal Troponin I at 0 & 2 hours nearly excludes MI (ESC 0/2 hr protocol).
- Repeat TnI in 1–3 hours if suspicion persists.
Interesting Fact
Troponin I remains elevated for up to 10 days, which helps diagnose MI even when patients present late - unlike CK-MB, which normalizes within 48–72 hours.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Cardiac Biomarkers
- Fourth Universal Definition of MI (2018)
- ESC 2020 NSTE-ACS Guidelines
- ACC/AHA ACS Guidelines
- Mayo Clinic Laboratories - Troponin I
- ARUP Consult - Cardiac Biomarkers
- NIH / MedlinePlus - Troponin Tests