[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Clinical skills](https://durgical.com/en/clinical-skills/) › [Reading lab results](https://durgical.com/en/clinical-skills/areas/labs/) › Troponin and natriuretic peptides

# Troponin and natriuretic peptides

- Interpretation

Troponin shows that heart muscle has been damaged; natriuretic peptides show that the heart is under strain, as in heart failure.

Updated Nov 13, 2026

## Key points

- Troponin above the 99th percentile = myocardial injury; a rise and/or fall plus ischaemia = myocardial infarction.
- Always read troponin as a series: the delta, not the single value, separates acute from chronic injury.
- ST-elevation myocardial infarction is diagnosed on the ECG; never wait for troponin to call for reperfusion.
- Natriuretic peptides are best for ruling out heart failure: BNP below 100 pg/mL or NT-proBNP below 300 pg/mL makes acute heart failure unlikely.
- Sacubitril–valsartan raises BNP (neprilysin breaks it down) but not NT-proBNP; follow NT-proBNP on that drug.

On this page

- The basics Key points
- What it is
- Reference values and concepts
- Reading it step by step
- Troponin and natriuretic peptide patterns
- Patterns and common mistakes
- Next step
- Memory aid
- Elsewhere in DurgiPedia

- Study Test yourself

- Connections Connections

## What it is

Cardiac troponin (I or T) is a protein of the heart muscle's contractile apparatus that leaks into the blood when myocytes are injured. High-sensitivity assays detect very small amounts, so the key reference point is the 99th percentile of a healthy population, which each assay defines and which may differ between men and women. A value above it means myocardial injury; it becomes myocardial infarction only when the values rise and/or fall and there is evidence of ischaemia (symptoms, new ECG changes, imaging or a coronary thrombus). That is why troponin is read as a series: the change between a first and a repeat sample (the delta) separates acute injury from a chronically raised level, as seen in kidney disease or stable heart disease. Many conditions other than coronary occlusion injure the myocardium: myocarditis, pulmonary embolism, sepsis, tachyarrhythmia, heart failure, takotsubo, aortic dissection and trauma. B-type natriuretic peptide (BNP) and its inactive fragment NT-proBNP are released by ventricular myocytes when the walls are stretched by volume or pressure. Their main use is to rule out heart failure in a breathless patient: a low value makes it unlikely. They rise with age, kidney failure and atrial fibrillation and are lower in obesity.

## Reference values and concepts

- High-sensitivity troponin: the upper reference limit is the assay's 99th percentile, often in ng/L and sometimes sex-specific; check your laboratory.
- Troponin starts to rise within a few hours of injury, peaks around a day and can stay raised for 1–2 weeks.
- Rapid protocols compare a sample on arrival with one at 1–3 hours, depending on the assay and validated pathway.
- Acute heart failure rule-out: BNP below 100 pg/mL or NT-proBNP below 300 pg/mL.
- Age-adjusted NT-proBNP rule-in for acute heart failure: above 450 pg/mL (under 50 years), 900 (50–75), 1800 (over 75).
- Non-acute (outpatient) heart failure is unlikely with BNP below 35 pg/mL or NT-proBNP below 125 pg/mL.

## Reading it step by step

- Look at the ECG first — ST elevation needs immediate reperfusion, whatever the troponin.
- Note the time from symptom onset to the first sample — a very early sample can still be normal after an infarct.
- Compare the first troponin with the assay's 99th percentile — above it means myocardial injury, not yet infarction.
- Repeat at the interval of your local pathway and calculate the delta — a significant change means acute injury.
- Ask whether the picture is ischaemic: pain, ECG, wall-motion changes — only then is it myocardial infarction.
- If not ischaemic, look for other causes: PE, myocarditis, sepsis, arrhythmia, dissection, kidney disease — treat the cause.
- In breathlessness, read BNP or NT-proBNP against the rule-out cut-off — a low value makes heart failure unlikely.
- Adjust the reading for age, kidney function, rhythm, weight and drugs — they shift natriuretic peptide levels.

## Troponin and natriuretic peptide patterns

| Result | Likely meaning | Think of |
| --- | --- | --- |
| Troponin rising and/or falling, ischaemic symptoms or ECG | Acute myocardial infarction | Plaque rupture (type 1), or supply–demand mismatch (type 2) from anaemia, hypotension, tachycardia |
| Troponin rising and/or falling, no ischaemia | Acute non-ischaemic myocardial injury | Myocarditis, PE, sepsis, takotsubo, contusion, stroke or subarachnoid haemorrhage |
| Troponin raised but stable on repeat | Chronic myocardial injury | Chronic kidney disease, stable heart failure, structural heart disease |
| Troponin below the 99th percentile on serial samples | Myocardial infarction unlikely | Other causes of chest pain; consider unstable angina if symptoms are typical |
| Low BNP or NT-proBNP | Heart failure unlikely | Lung disease, anaemia, obesity hypoventilation; consider obesity as a cause of falsely low values |
| High BNP or NT-proBNP | Raised wall stress | Heart failure, PE, atrial fibrillation, kidney failure, older age, sepsis |

## Patterns and common mistakes

- Calling every raised troponin an infarct: type 2 infarction and non-ischaemic injury (sepsis, PE, tachycardia) are common.
- Using a single troponin to rule out infarction when the sample was taken very soon after the pain began.
- Dismissing a stable, chronically high troponin in kidney disease as normal: it still carries risk, and a new delta still means acute injury.
- Reassuring because the troponin is normal in a patient whose ECG shows ST elevation or who is still in pain: treat the patient.
- Reading a high NT-proBNP in an older patient with kidney failure or atrial fibrillation as proof of heart failure; echo confirms it.
- Falsely low natriuretic peptides in obesity and in flash pulmonary oedema measured within the first hour.

## Next step

- ST elevation or ongoing ischaemic pain: activate the reperfusion pathway and call the senior or cardiology at once.
- Rising troponin with ischaemia: manage as acute coronary syndrome by the local protocol and discuss with cardiology.
- Raised troponin without ischaemia: look for and treat the cause (CT pulmonary angiography, echo, cultures) and repeat the troponin.
- High natriuretic peptide in a breathless patient: request an echocardiogram to confirm heart failure and its type.
- Record sample times on every troponin request so the next doctor can calculate the delta.

## Memory aid

Troponin = injury; delta + ischaemia = infarct. BNP low = look elsewhere.

## Test yourself

Think of the answer, then tap the question to see it.

## A 60-year-old man with 4 hours of chest pain has hs-troponin 8 ng/L, then 52 ng/L at 2 hours (99th percentile 14). What does this show?

A significant rise above the 99th percentile with ischaemic symptoms: acute myocardial infarction (non-ST elevation if the ECG has no ST elevation). Manage as acute coronary syndrome.

## A patient on dialysis has troponin 60 ng/L on arrival and 62 ng/L three hours later, with no chest pain. How is it read?

Raised but stable: chronic myocardial injury, common in kidney failure. There is no acute delta and no ischaemia, so it is not an infarct, though it still marks higher risk.

## A breathless 70-year-old has NT-proBNP 150 pg/mL. Is acute heart failure likely?

No. NT-proBNP below 300 pg/mL makes acute heart failure unlikely; look for another cause such as lung disease, PE or anaemia.

## Why is NT-proBNP preferred over BNP in a patient taking sacubitril–valsartan?

Sacubitril blocks neprilysin, which breaks down BNP, so BNP rises from the drug itself; NT-proBNP is not a neprilysin substrate and still reflects wall stress.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/clinical-skills/troponin-and-natriuretic-peptides/)

## Elsewhere in DurgiPedia

- [Cardiac troponin as a lab test](https://durgical.com/en/biochemistry/topics/cardiac-troponin-as-a-lab-test/)
- [Creatine kinase (CK) and CK-MB as lab tests](https://durgical.com/en/biochemistry/topics/creatine-kinase-and-ck-mb-as-lab-tests/)
- [Heart failure physiology](https://durgical.com/en/physiology/heart-failure-physiology/)
- [The ECG in ischemia and infarction](https://durgical.com/en/physiology/the-ecg-in-ischemia-and-infarction/)
- [Chest pain: ischemic, pericardial, pleural and other patterns](https://durgical.com/en/clinical-exam/chest-pain-ischemic-pericardial-pleural-and-other-patterns/)
- [Heart failure syndrome: left- and right-sided signs](https://durgical.com/en/clinical-exam/heart-failure-syndrome-left-and-right-sided-signs/)
- [Ischaemic heart disease](https://durgical.com/en/general-pathology/ischaemic-heart-disease/)

## Connections

## Related 5

- [Reading an ECG step by step](https://durgical.com/en/clinical-skills/reading-an-ecg-step-by-step/)
- [STEMI and its territories, and STEMI mimics](https://durgical.com/en/clinical-skills/stemi-and-its-territories-and-stemi-mimics/)
- [Electrolytes, urea and creatinine](https://durgical.com/en/clinical-skills/electrolytes-urea-and-creatinine/)
- [Echocardiography: transthoracic and transoesophageal](https://durgical.com/en/clinical-skills/echocardiography-transthoracic-and-transoesophageal/)
- [Coagulation tests: PT/INR, aPTT, fibrinogen and D-dimer](https://durgical.com/en/clinical-skills/coagulation-tests-pt-inr-aptt-fibrinogen-and-d-dimer/)

## Related conditions 8

- [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/)
- [Heart failure](https://durgical.com/en/conditions/heart-failure/)
- [Myocarditis](https://durgical.com/en/conditions/myocarditis/)
- [Pulmonary embolism](https://durgical.com/en/conditions/pulmonary-embolism/)
- [Takotsubo (stress) cardiomyopathy](https://durgical.com/en/conditions/takotsubo-cardiomyopathy/)
- [Aortic dissection](https://durgical.com/en/conditions/aortic-dissection/)
- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)

## In Pharmacology 2

- [Sacubitril/valsartan](https://durgical.com/en/pharmacology/sacubitril-valsartan/)
- [Nesiritide](https://durgical.com/en/pharmacology/nesiritide/)

[← All clinical skills](https://durgical.com/en/clinical-skills/)

Educational content; it does not replace supervised hands-on training, your institution's protocols or a prescriber's order. A procedure is learnt with a teacher and done only once you are trained to do it.

Sources: [Analytical and Clinical Aspects of Troponin Testing](https://www.ncbi.nlm.nih.gov/books/NBK507805/) (StatPearls (NCBI Bookshelf), 2026); [Natriuretic Peptide B Type Test](https://www.ncbi.nlm.nih.gov/books/NBK556136/) (StatPearls (NCBI Bookshelf), 2025).

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/clinical-skills/troponin-and-natriuretic-peptides/