Ohh I get it now after looking back. Suigetsu used the umbilical cord in Karin's desk thinking it was hers from when she was born or something (weird) which made us believe the DNA match was indeed with Karin, but that cord wasn't Karin's at all but Sakura's. Suigetsu causes drama even when he doesn't mean to lol. Still doesn't explain why Karin keeps an umbilical cord in her desk 