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This lesson covers two of the most common cardiac labs you’ll need to interpret for exams and in the clinical setting: BNP and troponin. Whether you’re prepping for your next med-surg exam, heading into your clinical rotation, or just trying to make sense of these labs during report, this lesson will help you feel more confident interpreting these values and knowing what they mean for your patient.

What is BNP?

BNP stands for B-type Natriuretic Peptide (you may also see it referred to as brain natriuretic peptide). It is a hormone that is released by the ventricles of the heart in response to increased stretch. This increased stretch stems from volume expansion and pressure overload on the ventricle, most specifically the left ventricle. That is why you’ll most often see BNP come into play when a patient is in heart failure or experiencing fluid overload.

What is a normal BNP?

A normal BNP level is typically less than 100 picograms per milliliter. If the level is elevated, it suggests the heart is struggling to manage the volume it’s got onboard and is indicative of congestive heart failure (CHF). The higher the BNP the more severe the CHF.

Clinical significance of BNP

So here’s how BNP is used clinically. Let’s say you’ve got a patient experiencing shortness of breath. The BNP can help determine if the cause is related to congestive heart failure or if it’s something else. For example, if the BNP is elevated, the cause of the SOB could be attributed to a CHF exacerbation. If the BNP is normal, then the SOB is due to another reason such as anemia or pneumonia. 

The BNP is also used to monitor a patient’s progress. If a patient with CHF has an elevated BNP that does not quickly return to baseline with treatment, this is an indicator of significantly higher mortality risk in the coming months. However, a patient whose BNP quickly returns to baseline after treatment is likely to have a better outcome.

Note that an elevated BNP does not automatically mean the patient has heart failure. Other causes for an elevated BNP include: 

In addition, falsely low levels can occur due to obesity and certain medications such as ACE inhibitors, beta blockers, and diuretics.

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What is Troponin?

Troponin is a cardiac biomarker that gets released when heart muscle is damaged. This makes it a key lab test in diagnosing myocardial infarction. There are two main types of troponin: troponin I and troponin T. Of the two, troponin I is more specific to cardiac tissue, so that is the one that is generally evaluated in the clinical setting when myocardial infarction is suspected. However, both troponins may be tested to give a more comprehensive picture of the heart’s severity of damage.

What is a normal troponin level?

Normal troponin I levels are < 0.03 to 0.04 ng/ml and they begin to rise within two to three hours of the onset of chest pain. The level will continue to rise until it reaches its peak in 12 to 48 hours. It will then decline over a period of four to ten days. Because it takes a few hours for the troponin to elevate and up to 48 hours for it to reach its peak, you’ll typically see troponins drawn in a series such as every four to six hours as the patient is being evaluated for myocardial infarction. 

Clinical examples of cardiac labs

Here are a few clinical examples of how you might utilize your knowledge of these two labs to coordinate the patient’s plan of care:

WHEN YOU SAY:YOU’RE SHOWING:
Mr. Wilson has a BNP of 1800 and is on a furosemide drip. His urine output has picked up, and his weight is down a kilo since yesterday. I expect his next BNP to be considerably lower.You’re showing that you’re watching the trend and evaluating the patient’s response to treatment.
Ms. Miller’s troponin just came back at 0.09, up from 0.03. She continues to have chest pain and is hypotensive.You’ve painted a picture of a patient experiencing active cardiac injury that the MD needs to take seriously.
She’s in mild respiratory distress with a BNP of 2100, 2+ leg edema, and a known CHF history. We started BiPAP and IV diuretics in the ED, and she’s already diuresing well. Cardiology is on board and wants her on telemetry monitoring.You’re using the BNP in combination with symptoms and treatment response to justify an appropriate level of care.
After stent placement, his troponin has decreased for the past three draws, chest pain is resolved, and ECG is showing normal sinus rhythm.You understand that a decreasing troponin is a sign that the cardiac event has passed and that the interventions worked.
His BNP was 450 pre-op, but he’s hemodynamically stable, no respiratory distress, and lungs are clear. We’ll monitor closely, but no signs of acute decompensation at this time.You’re showing that you’re not panicking over an elevated BNP if the clinical picture doesn’t support immediate concern.

TL;DR

To review, BNP tells us about volume overload and is a key diagnostic tool in evaluating heart failure. Troponin, specifically troponin I, tells us about cardiac cell injury and is used to evaluate patients with chest pain and suspected myocardial infarction.For more lessons on labs, click here!

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REFERENCES:

Beresford, P. (n.d.). BNP Fact Sheet. BLOOD SCIENCES – DEPARTMENT OF CLINICAL BIOCHEMISTRY – NORTH BRISTOL – NHS. https://www.nbt.nhs.uk/sites/default/files/BNP%20Fact%20Sheet.pdf

Cleveland Clinic. (2022, March 3). B-Type Natriuretic Peptide (BNP) Test: Normal Levels & Function. Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/22629-b-type-natriuretic-peptide

Maisel, A. (2002). B-Type Natriuretic Peptide Levels: Diagnostic and Prognostic in Congestive Heart Failure. Circulation, 105(20), 2328–2331. https://doi.org/10.1161/01.CIR.0000019121.91548.C2

Novack, M. L., & Zubair, M. (2025). Natriuretic Peptide B Type Test. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK556136/

Okamoto, R., Ali, Y., Hashizume, R., Suzuki, N., & Ito, M. (2019). BNP as a Major Player in the Heart-Kidney Connection. International Journal of Molecular Sciences, 20(14), 3581. https://doi.org/10.3390/ijms20143581

R, J. (2024, September 24). Troponin I vs. Troponin T: Understanding the Differences in Cardiac Markers. Ulta Lab Tests. https://www.ultalabtests.com/blog/heart-and-cardiovascular/troponin-i-vs-troponin-t-understanding-the-differences-in-cardiac-markers/

Stark, M., Kerndt, C. C., & Sharma, S. (2025). Troponin. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK507805/

Yoo, B.-S. (2014). Clinical Significance of B-type Natriuretic Peptide in Heart Failure. Journal of Lifestyle Medicine, 4(1), 34–38. https://doi.org/10.15280/jlm.2014.4.1.34

Last Updated on September 16, 2025 by Maureen Osuna, MSN, RN