The oral HIV diagnostic test is showing an alarming rate of false positives in San Francisco. “Forty-seven people who tested positive after using the OraQuick Advance HIV test in city clinics were not infected at all, the San Francisco Department of Public Health said this week.”

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  • Elliott

    Nowhere in this article did the most crucial information get shared. What is absolutely essential is to know the rate of false negatives (one quote says “there are no known instances” of a false negaive). Presumably, the alternative to the oral test is the blood test for each person who presented at the clinic. If the false negative rate is better than or comparable to the blood test and the test costs less than 4/5 the blood test then on a purely cost basis, it’s worth doing. I suppose you could argue that the false positive is stressful, but with a 1/4 false positive rate, full disclosure would mitigate the stress. At the same time there is benefit to not having to draw blood (stress and pain wise) so I think the balance is towards the oral test. Unfortunately, this withdrawal seems like a knee jerk reaction to the test not meeting expectations rather than a cost/benefit analysis. They get all bent out of shape over what is an interesting, but somewhat irrelevant detail.

    P.S. Home use with this high of a false positive rate is closer call given the innumeracy of so many people.

  • Anonymous

    re:”P.S. Home use with this high of a false positive rate is closer call given the innumeracy of so many people”

    Statements like that make me realize you really know very little about medicine Elliot. That is not a “close call”. HIV is still a very serious (at times terminal) diagnosis even with today’s HAART therapy. Do you propose allowing a test with a high “false positive” rate for home use? Don’t you remember the 1980′s and the stigma associated with that diagnosis that to a lesser extent still exists today. This is one test that definitely should not be allowed for home use….period. These results need to be reviewed betwen the doc and the patient including the need for further testing (western blot). There are times when you really come across as clueless dude.

  • Anonymous

    I suppose you could argue that the false positive is stressful, but with a 1/4 false positive rate, full disclosure would mitigate the stress.
    Hello? I would have a heart attack just on seeing a positive result. Even knowing the false positive rate. And I am in an extremely low risk group.
    Besides, if you have a “home test” soon you’ll have employers doing it or the insurance companies.
    As far as “pain” of having your blood drown – most of us stopped being afraid of needles sometime after the kindergarten.

  • Anonymous

    Wow, Genious Elliot thinks that a 25% false positive rate is acceptable for a home test for a disease as serious as HIV. This is the dumbest, most ignorant thing he has ever blogged.

  • gasman

    The article linked here give none of the data required to determine the false postive rate. Nor can we determine the more important numbers, positive and negative predictive value.

    This is epedemiology 101. A test used to screen populations with a low rate of disease should detect as many as possible. That is, fasle negatives should be avoided, even at the expense of creating more false positives. This is because the false negative is more harmful overall; in the end a missed individual with a false negative could turn into a fatality statistic.

    Once the vast majority are ‘exhonorated’ by the screening test, the next action is to perform a (usually) more costly, more invasive more time consuming test to sort out the positives. This allows confirmation (true positives) to advance to treatment, and false positives to know within a few hours.

    Would I get shook up by a positive screening? No, because I know where Mr. Willie has been these past 42 years, nor have I shared any needles or conducted any other behaviors at risk for transmission. The anxious person is probably the one who should be anxious because they have exercised behaviors that put them at risk for infection. We could call this wake up call a second chance for doing things right.

  • Elliott

    gasman makes some good points. Also, the false positive rate is not generally reported anywhere except newspaper articles. The relevant information is sensitivity, specificity, and accuracy. The number reported by the newspaper in this case is comparable to the diagnostic likelihood ratio. As far as I can tell, no home test currently approved for any other condition has significantly better measures than this test (pregnancy tests are far worse).

  • Elliott

    I don’t mean to say that the false positive rate is not important or not known, I meant to say that it is reported in the context of these other measures.

  • Anonymous

    It is not the article that said there was a 25% false positive rate. That is what Elliot said might be an acceptable false positive rate.

    I have had a couple of patients commit suicide after learning an HIV diagnosis despite face to face disclosure and proper follow up.

    Actually I am not against home testing. We really need to know the actual numbers here before turning it loose on a bunch of 19 year old college co-eds in Kansas that has a low disease prevalence rate.

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