NT-proBNP

When the heart makes its distress hormone, it first builds a larger precursor that is then snipped into two pieces: the active BNP and an inactive leftover called NT-proBNP. Both pieces enter the blood in equal numbers, so measuring the inactive fragment is another window onto how stretched and stressed the heart chambers are.

NT-proBNP rises and falls with the same forces that drive BNP, but it lingers longer in the blood and is more stable in the test tube. This makes it convenient and popular for diagnosing heart failure, gauging its severity, and following a patient's response to treatment over time.

Like BNP, NT-proBNP must be read against age and kidney function, both of which push it higher, and it tends to be lower in people with obesity. Different thresholds are used for ruling heart failure in or out, and the trend within a single patient is often more informative than comparing one person's number to another's.