5 ms·

1) To be pedantic, it detects your immune response (not the microorganisms directly) 2) "14% false alarm rate" => That makes it basically useless.

stormbrew 12y ago
False negatives are very bad. False positives not so much. Worst case is you send someone to a better test to find out if it's true. This is what they aim for with home pregnancy test kits, afaik, for pretty good reasons.
- Fomite 12y ago
  That very much depends on the disease in question. For these diseases, false negatives are bad. For diseases with intensive and dangerous treatments, false positives can be actively harmful to population health. This is commonly a problem in cancer screening.
  - cdcarter 12y ago
    Disease and plan. Almost every rapid HIV test out there is spoken about in "negative" or "maybe positive" terminology. If you get the two dots instead of one dot, you're referred to a physician who will administer a 4th gen test and probably a western bot, you aren't immediately started on ARVs.
- ekianjo 12y ago
  > False positives not so much. Really. No psychological effect then, you assume ?
SwellJoe 12y ago
1. Which, makes it potentially of limited use for HIV testing in high risk populations, since it can take months for immune response to be detectable by this sort of test. Not useless, certainly, as it is actually comparable to what most people get when they go to the doctor to get tested for HIV (not in accuracy, as your second point mentions, but in how long one would have to wait after exposure to know if you're infected). But, for populations not at significant risk, it would be a very good in-between test. 2. Early HIV tests had quite high false positive rates, and an imperfect false negative rate. That improved dramatically over the span of a few years. This is a new research device. It is not expected to be perfect. My first version of anything is never perfect. Technology futures can be hard to predict, but history indicates the following are consistently true: It'll get smaller, faster, cheaper, more precise. Will getting smaller, faster, cheaper, and more precise make this device an effective diagnostic tool? I'd be willing to bet it will.
lnanek2 12y ago
Yeah, false positives is what destroyed that company recently that had convenience store HIV tests. Lots of people who bought stock lost their shirts on that one.
Fomite 12y ago
Given the consequence of a false negative for both of those diseases (fatal if not treated), it makes perfect sense to optimize for a higher negative predictive value (if the test says you don't have it, you don't have it) versus a higher positive predictive value. While it would be ideal to have a high rate for both, that's the one I'd choose. And that false alarm rate is actually a dynamic function of the prevalence of the disease in the population being tested, which would make me hesitate to call it "useless", especially this early in its development. Those values, for the record, aren't that much worse than rapid diagnostic tests for influenza, which have a False Positive rate of about 6% and a false negative rate of about 18%, assuming 30% prevalence.
geuis 12y ago
How does a 14% false alarm rate make it useless? If it fails to turn positive for actual infection, I agree. But my understanding is its 114% positive, meaning if you have an infection its 100% positive and 14% positive when you aren't infected. Subsequent tests weed out the false positives. Out of 1000 people, say 100 are actually infected with syphilis. With 14% positive error rate, 140 would test positive. It's much better to only need the expensive 2nd test for 40 people rather than 1000.
- llamataboot 12y ago
  You are thinking about this wrong, what it actually means is that 14% of the time, it will detect positive. So say out of 1000 people, 1 is infected with syphilis. That person will tests positive, but so will 140 other people that don't have syphilis. So the test just referred 141 people to consultations and further testing, only 1 of which actually has the disease.

stormbrew 12y ago

False negatives are very bad. False positives not so much. Worst case is you send someone to a better test to find out if it's true. This is what they aim for with home pregnancy test kits, afaik, for pretty good reasons.

Fomite 12y ago
That very much depends on the disease in question. For these diseases, false negatives are bad. For diseases with intensive and dangerous treatments, false positives can be actively harmful to population health. This is commonly a problem in cancer screening.
- cdcarter 12y ago
  Disease and plan. Almost every rapid HIV test out there is spoken about in "negative" or "maybe positive" terminology. If you get the two dots instead of one dot, you're referred to a physician who will administer a 4th gen test and probably a western bot, you aren't immediately started on ARVs.
ekianjo 12y ago
> False positives not so much. Really. No psychological effect then, you assume ?

SwellJoe 12y ago

1. Which, makes it potentially of limited use for HIV testing in high risk populations, since it can take months for immune response to be detectable by this sort of test. Not useless, certainly, as it is actually comparable to what most people get when they go to the doctor to get tested for HIV (not in accuracy, as your second point mentions, but in how long one would have to wait after exposure to know if you're infected). But, for populations not at significant risk, it would be a very good in-between test. 2. Early HIV tests had quite high false positive rates, and an imperfect false negative rate. That improved dramatically over the span of a few years. This is a new research device. It is not expected to be perfect. My first version of anything is never perfect. Technology futures can be hard to predict, but history indicates the following are consistently true: It'll get smaller, faster, cheaper, more precise. Will getting smaller, faster, cheaper, and more precise make this device an effective diagnostic tool? I'd be willing to bet it will.

lnanek2 12y ago

Yeah, false positives is what destroyed that company recently that had convenience store HIV tests. Lots of people who bought stock lost their shirts on that one.

Fomite 12y ago

Given the consequence of a false negative for both of those diseases (fatal if not treated), it makes perfect sense to optimize for a higher negative predictive value (if the test says you don't have it, you don't have it) versus a higher positive predictive value. While it would be ideal to have a high rate for both, that's the one I'd choose. And that false alarm rate is actually a dynamic function of the prevalence of the disease in the population being tested, which would make me hesitate to call it "useless", especially this early in its development. Those values, for the record, aren't that much worse than rapid diagnostic tests for influenza, which have a False Positive rate of about 6% and a false negative rate of about 18%, assuming 30% prevalence.

geuis 12y ago

How does a 14% false alarm rate make it useless? If it fails to turn positive for actual infection, I agree. But my understanding is its 114% positive, meaning if you have an infection its 100% positive and 14% positive when you aren't infected. Subsequent tests weed out the false positives. Out of 1000 people, say 100 are actually infected with syphilis. With 14% positive error rate, 140 would test positive. It's much better to only need the expensive 2nd test for 40 people rather than 1000.

llamataboot 12y ago
You are thinking about this wrong, what it actually means is that 14% of the time, it will detect positive. So say out of 1000 people, 1 is infected with syphilis. That person will tests positive, but so will 140 other people that don't have syphilis. So the test just referred 141 people to consultations and further testing, only 1 of which actually has the disease.