There are multiple definitions:

1. nonperiodic neural activity(English)

   • PNA
   • Neurology

2. normalized protein nitrogen appearance(English)

   • also denoted as nPNA
   • MHD, nPCR, PCR
   • Nephrology, Proteins / proteomics, Nutrition
   • https://doi.org…87.2005.00214.x
   • https://doi.org…jren.2003.50005