Brain natriuretic peptide
BNP is initially synthesized as a 134–amino-acid
peptide called pre-pro BNP. The secondary cleaving of a 26–amino-acid signal
peptide results in the formation of pro-BNP or BNP 1-108. This molecule is
cleaved by furin, an endo-protease, into BNP 32 and N-terminal BNP (NT-BNP
1-76).
Major points to remember regarding BNP and NT-proBNP include:
- A major application of both BNP and proBNP testing is the evaluation of patients with congestive heart failure. If heart failure responds to therapy, concentrations of BNP and NT-proBNP should decline, indicating progress of therapy. If a patient does not respond, values may be increased gradually.
- In general, NT-proBNP is more stable (up to seven days at room temperature and up to four months if stored at −20°C) than BNP, which is not stable for a day even if the specimen is stored in a refrigerator. Therefore, BNP analysis must be performed as soon as possible after collecting the specimen.
- The cut-off level of BNP and NT-proBNP depends on age, as values tend to increase with advancing age. In general, heart failure is unlikely if the BNP value is less than 100 pg/mL and heart failure is very likely if the value is over 500 pg/mL. For NT-proBNP, the normal value for a person 50 years or younger is usually 125 ng/mL, but heart failure is unlikely if the NT-proBNP value is<300 pg/mL. However, heart failure is likely if the value is>450 pg/mL (>900 pg/mL in a patient of age 50 and above).
- Patients with end-stage renal disease and dialysis patients usually show higher BNP and NT-proBNP in serum than normal individuals.
