One of the experts here in this forum, Dr. Jose Gonzalez-Garcia, who is MD,MBBS,LMS,MRCP,MRCGP,PhD said that there can only be 2 ways to detect HIV during the window period:
1) PCR or NAT test, as early as 7 days post-possible exposure
2) HIV 1 and 2 antibodies + p24 antigen test (HIV DUO or HIV Combi test), as early as 28 days post-possible exposure.
See: http://www.medhelp.