« Go Back

False positive or not

Question: 

Thank you for your services.I have been working as a doctor in Germany for two months. During my pre-hospital screening test, my blood test was positive for HIV. Nine years ago, I had a similar incident in India where a screening test was positive. My doctor advised me to do a Western blot, P24 antigen and DNA PCR test, all of which were negative. I did not have any exposure.One year later, I got married and was tested every two years and was always negative. I gave birth to a healthy boy two years ago. The regular maternity checks for HIV were also negative. I am only sexually active with my husband. Is there a chance that this current test in Germany could be a false positive? How accurate are these tests in Germany for occupational medicine examination. What do I have to do now? Why would such an incident happen to me twice? I would really appreciate a feedback.

Answer: 

Hello,

Thank you for your inquiry. From what we gather from the question, you were asking about the HIV test you received in India 9 years ago which garnered a positive result. After this you received multiple HIV tests which all appear to have come back negative. Approximately 2 months ago, you received a positive HIV test in your pre-occupational screening in Germany. You were wondering if there a chance that this current test in Germany could be a false-positive.

From our observations, we perceive this to be a complex testing circumstance. Without more in depth information on the test you received in India approximately 9 years ago, we cannot speculate on the efficacy of HIV testing method occurrences of false-positives, and false-negatives. Based on the information we have on standard HIV testing methods in North America, we understand that standard HIV testing procedures leave little room for false-positives/false-negatives. Recommended testing methods such as Western Blot, P24 Antigen, and DNA PCR all have the correlating rates of accuracy:

Western Blot: After 4-6 weeks the accuracy is 99.9%, meaning that it is extremely unlikely to receive a false-positive/negative result (1).

P24 Antigen: The antigen on HIV that most commonly provokes an antibody response is the protein P24. This tests looks for this protein. The window period for the P24 antigen test is ONLY within first couple of weeks (once the body starts producing antibodies, this antigen is no longer detectable). The accuracy within this window period is 99.9%, meaning that it is also extremely unlikely to receive a false-positive/negative result (1).

DNA PCR: This test detects the genetic material of HIV itself. Within the window period of 2-3 weeks of exposure the accuracy of this test is 99.6% (1).

Given the above information regarding HIV testing accuracy, and the 3 tests that you have received; we would conclude that before you received the test in Germany, you were HIV negative.

However, your results appear to be inconsistent and you recent positive result warrants further exploration. In this case, our recommendation is that you refer to a physician for additional HIV screening to ensure the conclusiveness of your results.

Regards, AIDS Vancouver Helpline/Online, Hilary