Please help me understand Western blot results


I get tested for HIV about once a year at a local anonymous testing site. I tested HIV-negative in the summer of 2006, but a couple of weeks ago, I had a rapid fingerprick test come back "faintly" positive (i.e. a barely perceptible pink line at the "T" mark). The counsellor first told me I was HIV-negative and then looked again at the dipstick and wasn't sure. I requested another rapid fingerstick test and it was also faintly positive. I left without providing a blood sample for additional testing. The next day, I went to another testing site and the oral swab test had such a light pink line at the "T" mark that the counsellor wasn't sure what it meant. We did another finger-prick test and that was negative (no line). I went to my doctor two days later and submitted a blood sample for Elisa and Western Blot tests as well as another sample for HIV RNA viral load. The Elisas came back as positive as did the Western blot, but the HIV viral load came back as undetectable. The Western Blot band results are the following: P18 Reactive P24 Reactive P31 Indeterminate P40 Reactive GP41 Indeterminate P55 Reactive P65 Indeterminate GP120 Indeterminate GP160 Reactive

My questions are the following: What is the difference between "Indeterminate" and "Negative" results for the WB bands? (I had no "Negative" results, but I assume they exist.) According to some reading I've done online since getting these results, it seems that prior to 1993, my WB would have been considered "Indeterminate" due to the non-reactive P31 band. So, is there any hope -- especially since my viral load is undetectable and the longest I could have been infected is a year and I've obviously had no treatment -- that I might have some false positive results here?



Your ELISA is reactive (positive); your Western Blot (WB) is indeterminate. Indeterminate means the presence of any band pattern that does not meet the criteria for a positive test result. Negative means no bands. A positive WB is defined as reactivity to gp120/160 plus either gp41 or p24. You have reactivity to gp160 and p24; consequently, the odds are very strong that you are indeed HIV positive, despite the indeterminate results for gp120 and gp41. The causes of indeterminate Western Blot tests include serologic tests done during the process of seroconversion, late-stage HIV infection, cross-reacting nonspecific antibodies, infection with O strain or HIV-2, HIV vaccine recipients and technical or clerical errors.

The most important factor in evaluating indeterminate results is risk assessment. Folks in low-risk categories with indeterminate tests are almost never infected with either HIV-1 or HIV-2. I don't know what your risk profile is.

I would suggest you contact an HIV specialist in your area for additional follow-up. A repeat of your serological tests, plus a DNA PCR and evaluation of potential causes for indeterminate or false-positive results by the HIV specialist should firmly and definitively establish your HIV status one way or the other. From the information you presented, close follow-up for presumed primary HIV infection is certainly warranted.

Good luck. I'm here if you need me.

Dr. Bob