In this study, for the first time, we demonstrated that effective immuno-depletion of the precursor proBNP1-108 (up to 96% of the circulating proBNP1-108) revealed a clear cross-reactivity of proBNP in BNP assays and in a lesser extent of NTproBNP in routine clinical assays in HF management. The gene discussed is NPPB; the disease is hydrops fetalis.