NT-proBNP

UK laboratories commonly print an upper limit of 125 ng/L for adults under 75 and 450 ng/L for those over 75, because the level rises with age in the general population. NICE uses a separate figure of 400 ng/L for referral purposes, and the range differs in kidney disease.

NT-proBNP is a fragment of a hormone released by the heart muscle when its chambers are stretched by extra fluid or pressure. The more the heart is being stretched, the more of it appears in the blood. The N-terminal fragment is measured because it lasts longer in the blood than the active hormone, BNP.

Doctors request it when someone has breathlessness or swollen ankles to look for heart failure, and to decide who needs a heart ultrasound scan. It is also used to follow people who already have heart failure.

• Heart failure
• Older age, in the general population
• Kidney disease, because it is cleared by the kidneys
• A fast heart rhythm such as atrial fibrillation
• A blood clot in the lung, serious infection or lung disease with strain on the right side of the heart
• Being female, a little, in the general population

• Treatment of heart failure with water tablets and other heart medicines
• Being overweight, which lowers the level in the general population
• Recovery from an acute illness

• It rises with age, so a figure above the under-75 limit is common in healthy older people
• Reduced kidney function raises it without any change in the heart
• Being overweight lowers it, so a figure within range in a heavier person is read with that in mind

No fasting needed. Age, kidney function and body weight all affect the figure, so it is read with those in mind. For people already under a heart clinic, the trend over time matters more than one value.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.