Home HIV testing and false positives

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In the comments section, Colby Cosh makes a point which somehow totally escaped me when writing my post about HIV testing: home HIV tests have historically had a fairly high false positive rate, on the order of a percent. So, people could "discover" they have HIV when they actually don't.
That said, you have misrepresented the underlying issue just a teensy bit (and in a way that is surprising coming from you). The concern of the authorities is not with "people who discovered they had HIV", but with "people who got an AIDS diagnosis." These are not the same thing. As I understand it, the current generation of quick, cheap AIDS tests produce false positives about 1/200 of the time. The figure was presumably greater as long ago as 1987; if the false positive rate were as high as 1%, you can maybe see how a regulator would have misgivings about permitting OTC sale. The deliberate inculcation of panic about AIDS amongst heterosexuals increases the danger of psychological harm from the technology; even today people who had nothing like a 0.5% chance of having AIDS would be getting tested and freaking out when two little lines popped up instead of one. (Or just screwing up the damn directions on the box.)

The OraQuick Advance "oral fluid" test being discussed here has a false positive rate of about .2% (the blood version has better performance here). In 2003, there were about 4,000 HIV diagnoses in heterosexual, non-drug-using males and 7000 diagnoses in heterosexual females. Since there are 200-odd million people in this category, your risk is about .5% if your (heterosexual) behavior is about average. This means that if you get a positive result, there's only about a 70-80% chance that you're actually infected. Of course, if your behavior is low risk within this category, the chance that you're actually infected is even lower. Clearly, then, you need to take this into account before you take a home HIV test. However, it's not clear why this is a decision that the FDA is in a better position to make this decision for people than they are themselves.

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3 Comments

Given that doctors are equally bad at understanding the true probability of being infected, it's hard to get excited about the general public not understanding the implications of a positive result.

Presumably, whatever guidance and recommendations they gave to doctors in how to proceed after a positive result can be given to consumers as well. In fact, given people have bettr information about their own risk, in some sense, we should be able to do better with consumers than doctors.

Of course, the American judicial system has its own idiosyncratic solution to this dilemma: after the first few ruinous lawsuits from customers who suffer "psychological damage" (or worse) after getting a false positive, no company will be able to afford to market OTC HIV tests.

This discussion misses the point entirely. The unique selling proposition of a fast, saliva-based at-home HIV test is
checking your partner
.

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