ROC curves were constructed to determine the best cut-off value for NT-proBNP level in prediction of heart failure, with or without renal impairment and to assess whether this analysis can be used for diagnostic purposes by obtaining a sensibility and specificity of the test closer to 100%, starting from the null hypothesis that the value for NT-proBNP level cannot make the difference between the patients with HF, with or without renal impairment, and those without the disease (Figure 2 and Figure 3). Here, NPPB is linked to hydrops fetalis.