When to Refer to Cardiology with BNP Results
Patients with BNP levels >400 pg/ml or NT-proBNP >900 pg/ml should be urgently referred to cardiology as these levels are consistent with the diagnosis of heart failure and require specialist evaluation. 1, 2
BNP Thresholds for Cardiology Referral
- BNP <100 pg/ml or NT-proBNP <300 pg/ml: Heart failure is unlikely; cardiology referral not typically needed unless clinical symptoms suggest otherwise 1
- BNP 100-400 pg/ml or NT-proBNP 300-900 pg/ml ("grey zone"): Consider cardiology referral based on clinical context and risk factors, as these patients have increased mortality risk compared to those with normal levels 1, 2
- BNP >400 pg/ml or NT-proBNP >900 pg/ml: Urgent cardiology referral recommended as these levels have high positive predictive value for heart failure 1, 2
- BNP >1000 pg/ml: Immediate cardiology referral as these levels are associated with significantly worse 3-year survival 3
Age-Adjusted NT-proBNP Referral Thresholds
- **Age <50 years**: Refer if NT-proBNP >450 pg/ml 1, 4
- Age 50-75 years: Refer if NT-proBNP >900 pg/ml 1, 4
- Age >75 years: Refer if NT-proBNP >1800 pg/ml 1, 4
- **Severe renal failure and age <50 years**: Refer if NT-proBNP >1200 pg/ml 1
Special Considerations for Referral
- Elevated BNP with normal systolic function: Still refer to cardiology as this may indicate diastolic dysfunction with increased risk of adverse cardiovascular outcomes (HR: 4.79) 5
- Intensive care patients: Consider cardiology consultation for BNP >144 pg/ml (92% sensitivity, 86% specificity for cardiac dysfunction) 6
- Patients with suspected heart failure: Specialist review is associated with lower rates of all-cause and cardiovascular hospitalizations despite higher BNP levels 7
Important Confounding Factors
- Obesity (BMI >30 kg/m²): BNP levels may be falsely lower; consider using adjusted cut-off of 342 pg/ml for these patients 1
- Low BMI (<20 kg/m²): May have higher BNP levels than expected 1
- Renal dysfunction: Can elevate BNP levels independently of cardiac function 2
- Advanced age: Associated with higher baseline BNP levels 2, 4
- Atrial fibrillation: May increase BNP levels by 20-30% 2
Clinical Implications of Elevated BNP
- Each 100 pg/ml increase in BNP is associated with a 35% increase in relative risk of death over 1.5-3 years 1
- BNP >1000 pg/ml has significant clinical importance in both primary care and hospital settings 3
- BNP level is a strong predictor of risk of death and cardiovascular events in patients with heart failure or cardiac dysfunction 8
- Serial BNP measurements can monitor treatment response, with successful treatment resulting in measurable decreases in levels 1, 2
Common Pitfalls to Avoid
- Failing to refer patients with BNP >400 pg/ml: These levels are consistent with heart failure diagnosis and require specialist evaluation 1
- Ignoring elevated BNP in asymptomatic patients: Even mildly elevated levels are associated with increased risk of death, heart failure, atrial fibrillation, and stroke 1
- Not considering non-cardiac causes of elevated BNP such as pulmonary embolism, COPD, or renal dysfunction 2
- Missing the opportunity for early intervention: Specialist review is associated with better outcomes including reduced hospitalizations 7