BNP Interpreter Calculator

A BNP below 100 pg/mL is widely used as a rule-out threshold, with a negative predictive value commonly cited above 95% for acute heart failure in a patient presenting with dyspnea. Values between 100 and 400 pg/mL fall in a gray zone needing clinical correlation, and values above 400 pg/mL make heart failure likely.

NT-proBNP rises gradually with age even in people without heart failure, so a single cutoff would either miss heart failure in younger patients or over-diagnose it in older ones. Age-stratified rule-in thresholds -- commonly cited as roughly 450 pg/mL under age 50, 900 pg/mL from 50 to 75, and 1,800 pg/mL over 75 -- correct for that baseline drift, while the roughly 300 pg/mL rule-out threshold is used across all ages.

Both BNP and NT-proBNP are cleared from the blood partly through the kidneys, so reduced kidney function lets them accumulate to higher levels than the degree of heart strain alone would produce. That means a patient with significant chronic kidney disease can show an elevated marker without acute heart failure being the cause, which is why eGFR is an important piece of context rather than something to read the number in isolation from.

Yes -- obesity is associated with lower circulating BNP and NT-proBNP levels for a given degree of cardiac stress, so a marker that looks reassuringly normal can understate the severity of heart failure in an obese patient. This is a recognized limitation of natriuretic peptide testing, and clinicians generally weigh a higher BMI as a reason to trust the marker less, not as a reason to lower the diagnostic threshold by a precise, universally agreed amount.