No Additional Testing Required After 91 Days
You do not need a 4-month follow-up test after negative HIV Ag/Ab combo tests at 63 and 91 days post-exposure, as these results definitively rule out HIV infection from the original exposure. 1
Why Your Testing is Already Conclusive
The most recent CDC guidelines (2025) establish that the final, definitive HIV test to rule out infection should be performed 12 weeks (84 days) after exposure using laboratory-based Ag/Ab testing. 2 Your test at 91 days (13 weeks) exceeds this threshold and is therefore conclusive.
Key Timeline Considerations
- Fourth-generation Ag/Ab tests are considered definitive at 12 weeks post-exposure, based on data regarding antiretroviral washout periods and the window period of HIV tests 1
- Your 91-day test is one week beyond the CDC's recommended final testing timepoint, providing additional confidence 2
- The median window period for fourth-generation tests is only 18 days (16-24 days), meaning your 63-day test already had extremely high sensitivity 3
Understanding the Testing Algorithm
The CDC 2025 guidelines recommend a specific testing schedule only for persons who took post-exposure prophylaxis (PEP):
- Baseline testing: At time of exposure 2
- 4-6 weeks post-PEP initiation: Can be deferred if PEP started within 24 hours, full adherence achieved, and not considering PrEP 2
- 12 weeks post-PEP initiation (8 weeks post-completion): Final definitive test to rule out HIV 2
If you did not take PEP, standard testing timelines are even shorter, as there are no antiretroviral medications to suppress viral detection or delay seroconversion. 2
Why Extended Testing Beyond 12 Weeks is Unnecessary
- Antiretrovirals taken as PEP can suppress HIV viral load and delay seroconversion, which is why the 12-week timepoint accounts for medication washout 2
- Without PEP exposure, fourth-generation tests have a probability of false-negative results of only 0.01 at 42 days post-exposure 3
- Research demonstrates that fourth-generation Ag/Ab tests detect 82% of acute infections and have 99.9% specificity in high-prevalence populations 4
Important Caveat
This recommendation assumes no new HIV exposures occurred after your original exposure. 2 The CDC notes that certain PEP failures are attributable to subsequent exposures that may not be disclosed. 2 If you had additional potential exposures after your initial one, the testing timeline would restart from each new exposure.
Clinical Bottom Line
Your negative results at 63 and 91 days post-exposure definitively exclude HIV infection from the original exposure, assuming no subsequent exposures and no use of antiretroviral medications that could delay detection. 1 A 4-month (120-day) test adds no additional diagnostic value beyond your 91-day result. 2, 1