Is B-type natriuretic peptide (BNP) a reliable marker for diagnosing diastolic dysfunction or suspected diastolic heart failure in a patient with a preserved ejection fraction (EF) of 55-60%?

BNP as a Diagnostic Marker in Diastolic Heart Failure with Preserved Ejection Fraction

BNP is a moderately reliable but imperfect marker for diastolic dysfunction and heart failure with preserved ejection fraction (HFpEF), with its greatest utility being to rule out the diagnosis when levels are low, though normal BNP does not exclude HFpEF—particularly in younger, obese women. 1, 2

Diagnostic Performance in HFpEF

BNP has excellent negative predictive value (98%) for excluding heart failure when levels are below threshold, but its specificity is only moderate (60-76%), and importantly, BNP levels tend to be lower in HFpEF compared to heart failure with reduced ejection fraction. 3, 1, 2

Key Diagnostic Thresholds for Your Situation

For diagnosing HFpEF with your preserved EF of 55-60%:

• BNP <100 pg/mL makes heart failure unlikely but does not completely exclude it 3, 1
• BNP 100-500 pg/mL represents a gray zone requiring clinical correlation and echocardiography 3
• BNP >500 pg/mL strongly suggests heart failure 3

For NT-proBNP (if your lab uses this instead):

• NT-proBNP <300 pg/mL effectively rules out heart failure with 98% negative predictive value 3, 2
• NT-proBNP 400-2,000 pg/mL requires clinical correlation 2
• NT-proBNP >2,000 pg/mL strongly suggests heart failure 2

Critical Limitation: Normal BNP Does Not Exclude HFpEF

Approximately 29% of patients with confirmed HFpEF (proven by elevated pulmonary capillary wedge pressure on catheterization) have BNP levels ≤100 pg/mL. 4 This is a crucial pitfall—you can have genuine diastolic heart failure with normal BNP, especially if you are:

• Younger age 4, 5
• Female 4
• Obese (BMI >30-35 kg/m²) 4, 5
• Without atrial fibrillation 4
• Without chronic kidney disease 4

Obesity is the most important confounder, as each unit increase in BMI correlates with lower BNP levels, and severe obesity (BMI >35 kg/m²) can reduce BNP to only 60-100 pg/mL despite symptomatic heart failure. 2, 5

Correlation with Diastolic Dysfunction Severity

BNP levels correlate linearly with the severity of diastolic dysfunction and echocardiographic parameters of elevated left ventricular filling pressures. 6, 7 Specifically:

• NT-proBNP correlates strongly with invasive measurements of LV filling pressure (R=0.67, p<0.001) 7
• BNP increases progressively with worsening diastolic dysfunction grade 6, 7
• Elevated BNP in HFpEF patients is associated with enlarged left atrial volume, worse diastolic function parameters, and abnormal right ventricular function 4

However, BNP cannot distinguish between systolic and diastolic heart failure, though values tend to be lower in diastolic dysfunction. 3, 1

Prognostic Value in HFpEF

Even when BNP is elevated in HFpEF, it provides powerful prognostic information: elevated BNP is associated with a 4-fold increased risk of heart failure hospitalization (adjusted HR 4.0,95% CI 1.6-9.7) compared to normal BNP. 4

For every 500 pg/mL increase in NT-proBNP above baseline, mortality risk increases by 3.8% in patients with mild to moderate heart failure. 3, 1

Test Preparation Requirements

No special preparation is required for BNP testing—it does not need to be drawn in the morning, fasting is not necessary, and timing relative to meals is irrelevant. 3 The test can be performed at any time of day in the acute or outpatient setting. 3

Important Technical Considerations:

• BNP should be measured within 4 hours of blood draw for optimal stability 3
• NT-proBNP has higher in vitro stability than BNP if processing delays are anticipated 3
• Both assays are not standardized across laboratories, so results should be interpreted using your specific lab's reference ranges 3

Recommended Diagnostic Algorithm for Your Situation

Given your preserved EF of 55-60% and suspected diastolic dysfunction:

1. Obtain BNP or NT-proBNP (whichever your lab offers) without special preparation 3, 2

2. Interpret results accounting for your specific characteristics:

   • If you are obese (BMI >30), expect artificially lower values 2, 5
   • If you have reduced kidney function (GFR <60), expect higher values 3, 2
   • If you are older (>75 years), use age-adjusted thresholds 3, 2

3. If BNP <100 pg/mL or NT-proBNP <300 pg/mL: Heart failure is unlikely but not excluded, especially if you are young, female, or obese 3, 1, 4

4. If BNP 100-500 pg/mL or NT-proBNP 300-2,000 pg/mL: Proceed with comprehensive echocardiography including tissue Doppler imaging to assess diastolic function parameters 2, 7

5. If BNP >500 pg/mL or NT-proBNP >2,000 pg/mL: Heart failure is highly likely; obtain expedited echocardiography and specialist evaluation within 2 weeks 3, 2

Common Pitfalls to Avoid

Do not rely solely on BNP to exclude HFpEF in obese patients, young women, or those without atrial fibrillation—these groups frequently have falsely reassuring normal BNP levels despite genuine diastolic heart failure. 4, 5 Always integrate BNP results with clinical symptoms, physical examination findings, and confirmatory echocardiography with diastolic function assessment. 1, 2

Do not use BNP as a screening test in patients with low pre-test probability—its utility is maximized in patients with intermediate probability of heart failure. 3