What is BNP (Brain Natriuretic Peptide)?

B-Type Natriuretic Peptide (BNP)

BNP is a hormone secreted primarily by cardiac myocytes in response to mechanical stretch, serving as a biomarker for cardiac stress and heart failure that helps diagnose, risk-stratify, and monitor treatment response in patients with cardiac dysfunction. 1

Definition and Production

BNP (Brain or B-type Natriuretic Peptide) is:

• A neurohormone produced primarily by ventricular myocytes in response to:
  • Mechanical stretch
  • Pressure overload
  • Volume overload
  • Hypoxia 1
• Released initially as N-terminal pro-brain natriuretic peptide (NT-proBNP) and then enzymatically cleaved into:
  • The NT fragment (NT-proBNP)
  • The biologically active BNP (BNP1-32) 2, 3

Physiological Functions

BNP serves as a counter-regulatory system to the renin-angiotensin system with multiple effects:

• Promotes natriuresis (sodium excretion)
• Induces diuresis (increased urine output)
• Causes vasodilation
• Reduces blood pressure
• Inhibits renin, aldosterone, and vasopressin secretion 1, 2

Normal BNP Levels

Normal BNP levels vary by demographic factors:

Patient age	BNP (males)	BNP (females)
Young adults	< 25 pg/ml	< 25 pg/ml
45-59 years	< 100 pg/ml	< 100 pg/ml
> 60 years	< 98 pg/ml	Higher than males

Factors affecting BNP levels include:

• Sex (females typically have higher levels)
• Age (increases with age)
• Body mass index (higher BMI results in lower values)
• Renal function (impaired function increases levels) 1

Clinical Utility

Diagnostic Value

• Particularly useful in diagnosing heart failure in patients with acute dyspnea:
  • BNP < 100 pg/ml effectively excludes heart failure (90% sensitivity)
  • BNP > 400 pg/ml strongly suggests heart failure (76% specificity) 1
• Helps differentiate cardiac from pulmonary causes of dyspnea:
  • Normal BNP levels suggest pulmonary disease
  • Elevated BNP levels suggest cardiac disorder 2

Prognostic Value

• Higher BNP levels correlate with increased mortality risk
• Each 100 pg/ml increase in BNP increases the relative risk of death by 35% 1
• Serves as an independent predictor of cardiac death or deterioration of cardiac functional status 2

Treatment Monitoring

• BNP levels typically decrease with effective heart failure treatment
• Serial BNP measurements can help assess treatment efficacy in:
  • Acute cardiac decompensation
  • Outpatient heart failure management 1, 2

Clinical Considerations and Limitations

• BNP has limited value as a general screening test for heart failure due to false positives 2
• Non-heart failure conditions that can elevate BNP include:
  • Acute coronary syndromes
  • Pulmonary embolism
  • Renal failure
  • Sepsis
  • Atrial fibrillation
  • Pulmonary hypertension 1
• BNP should be used in combination with clinical judgment for optimal diagnostic accuracy 1

BNP vs. NT-proBNP

Both markers are clinically useful but have important differences:

• Half-life (BNP has shorter half-life)
• Stability (NT-proBNP is more stable)
• Detection range
• Sensitivity to hemodynamic changes 1

Therapeutic Applications

Nesiritide, the human recombinant form of BNP:

• Used in the treatment of acute heart failure
• Provides vasodilation and natriuretic effects
• Improves left ventricular function in patients with congestive heart failure 4, 5