NPPB and hydrops fetalis: The poor correlation between biomarker levels in saliva and serum may suggest an impaired transportation of NT-proBNP from the blood circulation into the saliva in HF patients, with a less efficient mechanism of converting proBNP (precursor molecule) by furin convertase into NT-proBNP, since its enzymatic activity in saliva is inhibited by histatins, preventing in situ generation of salivary NT-proBNP [23,24].