How should B-type natriuretic peptide (BNP) levels be interpreted in patients with impaired renal function?

From the Guidelines

B-type natriuretic peptide (BNP) levels should be interpreted with caution in patients with impaired renal function, as these patients typically have higher baseline BNP values. When evaluating BNP in renal impairment, clinicians should use higher diagnostic thresholds than those applied to patients with normal kidney function. For patients with an estimated glomerular filtration rate (eGFR) below 60 mL/min/1.73m², consider using approximately double the standard cutoff values, as recommended by the KDIGO 2012 guideline 1. For example, while a BNP level above 100 pg/mL might suggest heart failure in patients with normal renal function, levels up to 200-300 pg/mL may be acceptable in those with significant kidney disease. The elevated BNP levels in renal dysfunction occur because the kidneys are responsible for clearing natriuretic peptides from circulation, so decreased kidney function leads to accumulation of BNP in the bloodstream, as explained in the European Heart Journal study 1. Additionally, many patients with chronic kidney disease have concurrent cardiac abnormalities that can independently raise BNP levels. When evaluating a patient with renal impairment, always integrate BNP results with clinical findings, imaging studies, and other diagnostic information rather than relying solely on absolute BNP values. Some key points to consider when interpreting BNP levels in patients with renal insufficiency include:

• The influence of age, gender, ethnicity, and non-HF pathologies on BNP and NT-proBNP values, as discussed in the Circulation study 1
• The impact of obesity on BNP and NT-proBNP concentrations, with an inverse relationship between body mass index (BMI) and BNP and NT-proBNP concentrations in patients with and without CHF, as noted in the Anaesthesia study 1
• The potential for false increased concentrations of BNP in patients receiving nesiritide therapy, as mentioned in the Circulation study 1
• The high intra-individual biological variability of BNP and NT-proBNP, which may cause clinicians to misinterpret changing concentrations, as highlighted in the Circulation study 1. Serial measurements tracking trends in BNP levels over time are more valuable than single readings in these patients, and changes in BNP or NT-proBNP concentrations must be used cautiously, as emphasized in the Anaesthesia study 1.

From the Research

Interpretation of BNP Levels in Renal Insufficiency

• B-type natriuretic peptide (BNP) levels can be elevated in patients with renal insufficiency, making interpretation of BNP levels challenging in this population 2, 3, 4.
• The presence of renal dysfunction can overestimate BNP values, as BNP is cleared by the kidneys and impaired renal function can lead to increased BNP levels 2, 4.
• Studies have shown that BNP levels are elevated in patients with chronic kidney disease (CKD) and can predict renal outcome, with higher BNP levels associated with a poorer renal outcome 5.
• The clinical utility of BNP in dialysis patients is limited by impaired renal clearance and preexisting left ventricular abnormalities, which can confound the interpretation of BNP levels 4.
• BNP testing is best used as a 'rule out' test for suspected cases of new heart failure in breathless patients presenting to either the outpatient or emergency care settings, but should not be used in isolation from the clinical context 6.

Factors Affecting BNP Levels in Renal Insufficiency

• Age, gender, and body mass index (BMI) can influence BNP levels, with BNP levels rising with age and being affected by gender and BMI 2, 3, 6.
• Comorbidities such as heart failure, coronary artery disease, and pulmonary hypertension can also affect BNP levels, making interpretation of BNP levels in patients with renal insufficiency more complex 3, 4.
• The use of certain medications, such as sacubitril/valsartan, can also affect BNP levels, highlighting the need for careful consideration of the clinical context when interpreting BNP levels in patients with renal insufficiency 2.

Clinical Applications of BNP Testing in Renal Insufficiency

• BNP testing can be useful in diagnosing heart failure in patients with renal insufficiency, but should be used in conjunction with other diagnostic tests and clinical evaluation 2, 3, 6.
• BNP levels can also be used to monitor disease progression and response to treatment in patients with heart failure and renal insufficiency, but should be interpreted with caution due to the potential for confounding factors 4, 5.