NPPB and type 2 diabetes mellitus: It is also important to note that some included studies were conducted in specific clinical subpopulations; for example, the NT-proBNP prognostic data from Malachias et al. [18] were derived from patients with type 2 diabetes mellitus, and the metabolic profiling work by Lerman et al. [13] analyzed patients enrolled in a clinical trial setting, which may influence external validity.