S/CO means Signal-To-Cutoff Ratio. Top keep complicated thing simple, S/Co is just another way of confirming positive test results. Or, if you want it in a scientific way, it is a ratio that predicts supplemental test-positive results. It is a calculated value.
S/CO is initially and primarily used for Hepatitis C
but, theoretically, can be used for many other diseases and conditions. S/CO is considered positive if it is >1. Your fiancee's results are
As to the other tests you mentioned, both ELISA
and IFA are used for detection of certain types of proteins
. ELISA usually detects ANTIGENS, IFA detects ANTIBODIES
So, the bottom line is that you do not have any reason to be anxious at this time.
Hope this helps.