The change in you index value is, by itself, not definitive. However, now your chances, at this index value of having a true positive, are 50-50. So there is also a 50% chance that this is negative. You are correct you need a western blot but another way to sort this out would be to ask your partner to be tested. If she is negative, then there is less worry about this. I doubt that this is a true scab if it has lasted three months – it must be something else other than a scab or it would have fallen off by now, i think.
If you want help with the western blot, our clinic can order one at a Quest lab near you.