BNP (brain natriuretic peptide) and NT-proBNP are blood markers of heart failure. Despite the name, BNP is produced primarily by the heart, not the brain — the name reflects that it was first isolated from pig brain. BNP rises when heart chambers are stretched, making it a sensitive marker for heart failure. The bnp test is essential in evaluating shortness of breath and confirming or excluding heart failure as the cause. This guide covers what BNP measures, normal ranges, and how it’s used clinically.
BNP vs NT-proBNP
The proBNP precursor is cleaved into BNP (active hormone) and NT-proBNP (inactive fragment). Either can be measured:
- BNP: shorter half-life, more affected by treatment
- NT-proBNP: longer half-life, more stable
Both provide similar information. Different labs use different assays. Reference ranges differ between BNP and NT-proBNP, so comparing values requires knowing which test was performed.
Reference ranges
BNP:
- Under 100 pg/mL: heart failure unlikely
- 100-400 pg/mL: gray zone
- Above 400 pg/mL: heart failure likely
NT-proBNP:
- Under 300 pg/mL: heart failure unlikely
- Age-adjusted upper limits: under 50 (450), 50-75 (900), over 75 (1800)
Clinical use in heart failure
BNP/NT-proBNP is most useful for:
Diagnosis: In patients with dyspnea, normal BNP essentially excludes heart failure as the cause. Elevated BNP supports heart failure diagnosis.
Prognosis: Higher BNP correlates with worse outcomes.
Treatment monitoring: Falling BNP suggests improving heart failure; rising BNP suggests worsening or inadequate treatment.
Risk stratification: In acute heart failure, BNP guides treatment intensity decisions.
The American Heart Association incorporates BNP/NT-proBNP in heart failure guidelines.
Causes of elevated BNP beyond heart failure
- Heart failure (most common)
- Pulmonary embolism
- Atrial fibrillation
- Kidney disease
- Severe sepsis
- Pulmonary hypertension
- Older age (mild baseline elevation)
Causes of falsely low BNP
- Obesity (BNP levels can be falsely low; NT-proBNP less affected)
- Recent acute heart failure that has been treated
- Constrictive pericarditis (sometimes shows low BNP despite heart failure-like symptoms)
Sacubitril-valsartan and BNP
Sacubitril-valsartan (Entresto) is a heart failure medication that inhibits BNP breakdown. Patients on sacubitril-valsartan have artificially elevated BNP that doesn’t reflect heart failure status. NT-proBNP is unaffected by sacubitril-valsartan and is preferred in these patients.
Frequently Asked Questions
Do I need to fast for BNP testing?
No, fasting isn’t required.
What does an elevated BNP mean?
Most commonly heart failure, but other conditions can elevate it. Clinical context determines interpretation.
Can BNP be elevated without heart failure?
Yes. Pulmonary embolism, kidney disease, atrial fibrillation, and other conditions can elevate BNP.
Should obese patients use BNP or NT-proBNP?
NT-proBNP is preferred since BNP is artificially low in obese patients.
How quickly do BNP levels change?
BNP changes within hours of treatment changes. NT-proBNP changes more slowly.
The bottom line on the BNP test
BNP and NT-proBNP are essential markers for diagnosing and monitoring heart failure. Normal values largely exclude heart failure; elevated values support diagnosis. Multiple non-cardiac causes of elevation exist. Discuss results with your healthcare provider in clinical context, particularly considering medications like sacubitril-valsartan that affect BNP measurement.