Which factor does NOT affect BNP/NT-proBNP interpretation?

• A. Age
• B. Renal function
• C. Obesity
• D. Sex (Male)

Answer: (D)

The main idea is that BNP and NT-proBNP levels are shaped by factors beyond heart failure itself, so understanding how these noncardiac factors influence interpretation is essential. BNP and NT-proBNP rise with myocardial stretch, but their circulating levels are also affected by age, renal function, and body composition. As people age, BNP/NT-proBNP levels tend to drift upward, so age can raise baseline values and affect where diagnostic cutoffs lie. Renal function has a strong impact because NT-proBNP is cleared by the kidneys; when kidney function is reduced, levels go up even without new heart failure, making interpretation more complex. Obesity tends to lower circulating BNP/NT-proBNP, which can mask elevated levels in someone with heart failure and lead to underestimation of severity if not considered.

Sex differences do exist, but in routine practice the diagnostic thresholds are not consistently adjusted by sex, so sex does not reliably alter interpretation in the same way the other factors do. Therefore, the factor that does not meaningfully affect interpretation in typical clinical use is male sex.