NPPB and hydrops fetalis: Similarly, Delles et al. [15] demonstrated that elevated phenylalanine independently predicted incident HF hospitalization in over 12,000 participants across two large cohorts (HR 1.29, p = 0.002; replicated HR 1.23, p = 0.023), improving risk reclassification by 21% (p = 0.007) beyond NT-proBNP.