Similar to troponin, BNP itself was a patented assay sold by only one vendor. NT-proBNP was not patented and so there are multiple vendors who have an FDA-approved assay. Some things to note about NT-proBNP are:
Individuals with heart failure typically have approximately 8-10 times higher levels of NT-proBNP versus BNP. This is important. Physicians used to BNP will notice much higher levels with NTproBNP. About half of this difference is due to the difference in molecular weight of the two molecules (NT-proBNP is about 2.5 times larger than BNP). Also, NT-proBNP has higher in vivo stability as mentioned earlier.
Both BNP and NT-proBNP increase with increasing age and decreasing renal function.
NT-proBNP values tend to be more precise: NT-proBNP assays generally have good within-run and total precision, with total CV ranging from 2.9% to 6.1%. In contrast, total CV for BNP ranges from 9.9% to 12.5%, which is approximately 2-3 fold higher.
NT-proBNP assays are harmonized (all vendors use the same detection antibody).