Can a patient with one kidney have elevated N-terminal pro b-type natriuretic peptide (NT-proBNP) levels?

Elevated NT-proBNP Levels in Patients with One Kidney

Yes, patients with one kidney can have elevated NT-proBNP levels due to reduced renal clearance, as NT-proBNP is primarily cleared by the kidneys (55-65% of total body clearance). 1

Mechanism of Elevated NT-proBNP in Single Kidney Patients

NT-proBNP levels are significantly affected by kidney function through several mechanisms:

1. Reduced Clearance: NT-proBNP is cleared passively by organs with high blood flow, with the kidneys accounting for 55-65% of total body clearance 1, 2

2. Compensatory Hyperfiltration: A single kidney often undergoes compensatory hyperfiltration, which may not fully compensate for the loss of the second kidney's clearance capacity

3. Impact on NT-proBNP/BNP Ratio: Deteriorating kidney function increases both BNP and NT-proBNP levels, but has a more pronounced effect on NT-proBNP, resulting in an increased NT-proBNP/BNP ratio 3

Clinical Implications

Diagnostic Considerations

When interpreting NT-proBNP levels in patients with one kidney:

• Adjust Cut-off Values: Standard cut-offs for heart failure diagnosis should be modified based on kidney function 1

  • For patients with GFR <60 mL/min/1.73 m², use a higher NT-proBNP cut-off of 1200 ng/L 1, 2
  • For patients with severe renal dysfunction (GFR <30 mL/min/1.73 m²), interpretation becomes even more challenging 1

• Consider False Positives: Elevated NT-proBNP in single kidney patients may not necessarily indicate heart failure 1

Risk Assessment

Despite the effect of kidney function on NT-proBNP levels:

• NT-proBNP remains a significant predictor of mortality and cardiovascular events even in patients with kidney dysfunction 4
• In CKD patients, NT-proBNP levels >384.9 pg/mL were associated with increased risk of mortality or need for renal replacement therapy (sensitivity 70.8%, specificity 72.7%) 4

Practical Approach to Interpretation

When evaluating NT-proBNP levels in a patient with one kidney:

1. Assess Baseline Kidney Function: Determine the patient's eGFR, as this inversely correlates with NT-proBNP levels (r = -0.579) 3

2. Use Modified Cut-offs:

   • For ruling out heart failure: Use higher threshold than the standard 300 ng/L
   • For ruling in heart failure: Consider kidney function-adjusted values 1

3. Look for Trends: Serial measurements may be more valuable than absolute values

4. Integrate Clinical Context: Consider other causes of elevated NT-proBNP beyond heart failure:

   • Volume overload
   • Hypertension
   • Anemia (lower hematocrit correlates with higher NT-proBNP) 5
   • Proteinuria 5

Common Pitfalls to Avoid

• Using Standard Cut-offs: Applying standard NT-proBNP cut-offs without adjusting for kidney function
• Over-diagnosing Heart Failure: Attributing elevated NT-proBNP solely to cardiac dysfunction without considering renal contribution
• Ignoring Other Biomarkers: Relying exclusively on NT-proBNP without considering other cardiac markers
• Neglecting Clinical Assessment: Failing to integrate NT-proBNP results with physical examination findings and symptoms

In conclusion, while a single kidney can cause elevated NT-proBNP levels due to reduced clearance, these values still provide valuable prognostic information when interpreted with appropriate kidney function-adjusted thresholds.