This term got 24 hits on 22.10.2011, on lists of abbreviations and acronyms, and is thus likely to have been retired
Medical » British Medicine
National Association of Theatre Nurses
National Association of Training Nurses
NATIONALITY - NATIS - NATKD - NATL - NATM - NATO - NATONG - NATOPS - NATP - NatPaCT Programme XX
"NATN." Abbreviations.com. STANDS4 LLC, 2015. Web. 4 Aug. 2015. <http://www.abbreviations.com/NATN>.