Aa
Re: HIV Testing Clarification
Hi Drs. Handsfield and Hook,
Could you please clarify a few questions regarding HIV testing for me.
1. I have read in a recent post answered by Dr. Handsfield that the Oraquick Advance rapid test has recently been shown to have false negatives. Could you give me the percentages of false negatives and why they might occur. Previously, it was thought the test gave no false negatives.
2. Is the timeline for testing with the Oraquick Advance rapid test and standard antibody tests the same in regards to when the test is conclusive, regardless of the risk. You both have stated 8 weeks as being conclusive.
3. If so, then why do you say at times that testing should still be done after 3 months. Are you taking into account other individual factors that may delay antibody development due to certain conditions or other factors?
And what would those factors be? For the normal individual is 8 weeks conclusive?
Thank you both for the clarification, it would be great to hear a response from both of you and your valued opinions regarding this matter.
Thanks again,
Bill
Could you please clarify a few questions regarding HIV testing for me.
1. I have read in a recent post answered by Dr. Handsfield that the Oraquick Advance rapid test has recently been shown to have false negatives. Could you give me the percentages of false negatives and why they might occur. Previously, it was thought the test gave no false negatives.
2. Is the timeline for testing with the Oraquick Advance rapid test and standard antibody tests the same in regards to when the test is conclusive, regardless of the risk. You both have stated 8 weeks as being conclusive.
3. If so, then why do you say at times that testing should still be done after 3 months. Are you taking into account other individual factors that may delay antibody development due to certain conditions or other factors?
And what would those factors be? For the normal individual is 8 weeks conclusive?
Thank you both for the clarification, it would be great to hear a response from both of you and your valued opinions regarding this matter.
Thanks again,
Bill
MEDICAL PROFESSIONAL
My original response above wasn't entirely clear. The lower test performance of rapid tests relates mostly to the early period of new HIV infections, not in longstanding infection. Others have also raised concerns after reading this thread. Please see the following new thread for a more detailed explanation of these issues: http://www.medhelp.org/posts/HIV-Prevention/Accuracy-of-rapid-tests/show/1316320
MEDICAL PROFESSIONAL
Welcome to the forum, and aloha. (This reply originates from my place at Poipu Beach, Kaua'i.) Directly to your questions.
1) It is correct that more recent research has suggested a higher proportion of false negatives with rapid testing than previously realized. My recollection is that it's around 15%, i.e. meaning a negative result remains at least 85% reliable. However, the newer studies were rather small, and there is a large margin of error. To my knowledge the exact reasons are not known. However, false negative results do not occur repeatedly in the same person; so two negative results with rapid tests is virtually 100% reliable.
2) The window period ("time line") is about the same for the lab-based and rapid tests. 8 weeks usually is conclusive.
3) This has been explained before, but not for a while. It bears repeating. The reliability of test results is not dependent on the test alone, but depends on the overall risk context. Assume a worried person at low risk, let's say heterosexual exposure with a 1% chance of an infected partner and, if s/he is infected, 1 chance in 1000 of catching HIV. The chance that person will catch HIV is 0.01 x 0.001 = 0.00001, or 1 in 100,000. Test at 4 weeks, with a test with 90% reliability. With a negative result, the chance the person has HIV drops tenfold, to 1 in a million. Pretty good odds.
Now assume a much higher risk exposure, say a known infected partner and anal sex, which has a 1% chance of transmission. Before testing, the chance of infection is 1 in 100. Test at 4 weeks, 90% reliability, the infection chance is now 1 in 1,000. A lot better, but still much to high to stop testing. Test at 6-8 weeks, 99% test reliability: chance of infection is now 0.01 x 0.01 = 0.0001. One in 10,000 very good odds. But still maybe not high enough to relax. Such a person needs another test at 3+ months.
The higher the risk, the more important to have a test result that approaches 100% certainty. The lower the risk, the greater the confidence in a negative result even if done early. Same test, different context, and therefore different reliability of results.
I hope this helps. Best wishes-- HHH, MD
1) It is correct that more recent research has suggested a higher proportion of false negatives with rapid testing than previously realized. My recollection is that it's around 15%, i.e. meaning a negative result remains at least 85% reliable. However, the newer studies were rather small, and there is a large margin of error. To my knowledge the exact reasons are not known. However, false negative results do not occur repeatedly in the same person; so two negative results with rapid tests is virtually 100% reliable.
2) The window period ("time line") is about the same for the lab-based and rapid tests. 8 weeks usually is conclusive.
3) This has been explained before, but not for a while. It bears repeating. The reliability of test results is not dependent on the test alone, but depends on the overall risk context. Assume a worried person at low risk, let's say heterosexual exposure with a 1% chance of an infected partner and, if s/he is infected, 1 chance in 1000 of catching HIV. The chance that person will catch HIV is 0.01 x 0.001 = 0.00001, or 1 in 100,000. Test at 4 weeks, with a test with 90% reliability. With a negative result, the chance the person has HIV drops tenfold, to 1 in a million. Pretty good odds.
Now assume a much higher risk exposure, say a known infected partner and anal sex, which has a 1% chance of transmission. Before testing, the chance of infection is 1 in 100. Test at 4 weeks, 90% reliability, the infection chance is now 1 in 1,000. A lot better, but still much to high to stop testing. Test at 6-8 weeks, 99% test reliability: chance of infection is now 0.01 x 0.01 = 0.0001. One in 10,000 very good odds. But still maybe not high enough to relax. Such a person needs another test at 3+ months.
The higher the risk, the more important to have a test result that approaches 100% certainty. The lower the risk, the greater the confidence in a negative result even if done early. Same test, different context, and therefore different reliability of results.
I hope this helps. Best wishes-- HHH, MD
MEDICAL PROFESSIONAL
It makes no difference whether or not Dr. Hook or I have seen someone with seroconversion delayed beyond 8 weeks. It can happen, but it's very rare.
As to your second question, I can only shake my head in wonder. We don't insist on very much from questioners, but we do expect them to read our replies. Did the odds calculations above make no difference at all? I don't know how to explain it any more clearly and I'm not going to try.
This thread is over. I will delete any further anxiety-driven comments without reply.
As to your second question, I can only shake my head in wonder. We don't insist on very much from questioners, but we do expect them to read our replies. Did the odds calculations above make no difference at all? I don't know how to explain it any more clearly and I'm not going to try.
This thread is over. I will delete any further anxiety-driven comments without reply.
Hi Dr. Handsfield,
Is it true that neither yourself nor Dr. Hook has ever seen a negative test turn positive after 8 weeks? Please answer this question for me.
And if so, after a possible exposure/risk, would a standard lab based test after 8 weeks be conclusive for all practical purposes of being assured that one did not acquire hiv?
Mahalo for your time and knowledge,
Bill
Is it true that neither yourself nor Dr. Hook has ever seen a negative test turn positive after 8 weeks? Please answer this question for me.
And if so, after a possible exposure/risk, would a standard lab based test after 8 weeks be conclusive for all practical purposes of being assured that one did not acquire hiv?
Mahalo for your time and knowledge,
Bill
Hi Dr. Handsfield,
Aloha and thank you for your informative reply. Do you reside on Kaui? I am in Oahu.
Sorry, just a few more questions for clarification based on the information you provided.
1. Is it correct that if 2 Oraquick Advance rapid tests are done at different times after 8 weeks the possiblility of a false negative can be ruled out? Is the fingerstick test better than oral fluid? And does the incidence of increased false negatives only apply to rapid tests and not standard lab-based tests?
2. Is it correct that neither yourself, Dr. Hook, or any other experts have not seen a negative rapid or standard lab-based test turn positive after 8 weeks regardless of the risk involved?
3. It seems that the term "conclusive" relates to mathematical odds and that the closer to 3 months the closer the test approaches 100% reliablility, even though there has not been a negative result turning positive after 8 weeks.
Once again, mahalo for all of your help, Bill.
Aloha and thank you for your informative reply. Do you reside on Kaui? I am in Oahu.
Sorry, just a few more questions for clarification based on the information you provided.
1. Is it correct that if 2 Oraquick Advance rapid tests are done at different times after 8 weeks the possiblility of a false negative can be ruled out? Is the fingerstick test better than oral fluid? And does the incidence of increased false negatives only apply to rapid tests and not standard lab-based tests?
2. Is it correct that neither yourself, Dr. Hook, or any other experts have not seen a negative rapid or standard lab-based test turn positive after 8 weeks regardless of the risk involved?
3. It seems that the term "conclusive" relates to mathematical odds and that the closer to 3 months the closer the test approaches 100% reliablility, even though there has not been a negative result turning positive after 8 weeks.
Once again, mahalo for all of your help, Bill.
You are reading content posted in the HIV - Prevention Forum
Condoms are the most effective way to prevent HIV and STDs.
PrEP is used by people with high risk to prevent HIV infection.
Can I get HIV from surfaces, like toilet seats?
Can you get HIV from casual contact, like hugging?
Frequency of HIV testing depends on your risk.
Post-exposure prophylaxis (PEP) may help prevent HIV infection.
