Oral sex does not cause HIV. It's not low risk, it's NO risk. No risk means there is no reason to get tested.
There is nothing you can add to make it a risk. Period, blood, etc. will not make this a risk. If air and saliva inactivate the virus, that would include all hiv and under this circumstance as well. So, no, it is still not risk at all. The only ways adults get HIV is from unprotected vaginal or anal sex or sharing IV drug needles.