BNP

UK laboratories commonly print an upper limit of 100 ng/L; the level rises with age and with reduced kidney function in the general population, and is lower in people who are overweight. NICE uses 400 ng/L as a referral figure.

BNP, B-type natriuretic peptide, is a hormone released by the heart muscle when its chambers are stretched by extra fluid or pressure. It acts on the kidneys to remove salt and water. It is the active hormone; the NT-proBNP test measures a longer-lasting fragment of the same molecule, and the two give different numbers.

Doctors request it when someone has breathlessness or swollen ankles to look for heart failure, and to decide who needs a heart ultrasound scan. Most UK laboratories now offer NT-proBNP instead, but some still use BNP.

• Heart failure
• Older age, in the general population
• Kidney disease
• 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

• Treatment of heart failure with water tablets and other heart medicines
• Being overweight, which lowers the level in the general population
• Sacubitril, a heart failure medicine, raises BNP while lowering NT-proBNP, so the two tests can move in opposite directions on it

• It rises with age, so a figure above the range is common in healthy older people
• Reduced kidney function raises it without any change in the heart
• The sample must reach the laboratory promptly, as BNP breaks down quickly

No fasting needed; the sample should reach the laboratory promptly. Age, kidney function and body weight all affect the figure. Do not compare a BNP with an NT-proBNP; they are different scales.

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