By Adem Lewis / in , , , , , , , , , , , , , , , , , , , , , , , , , , /

welcome to another MedCram lecture and
board vitals question this one comes from the internal medicine and pathology
question banks here’s the question in a move that could increase the nation’s
blood supply by at least four percent a year the FDA has recommended an end to a
lifetime ban on blood donations for gay men the FDA issued draft guidance in
2015 regarding the acceptance of men who have sex with men or MSM to donate blood
the window for HIV – na t which is nucleic acid testing is approximately
nine days and the incidence of HIV in the MSM population is about 1% per year
in other words that’s one per hundred persons in one year based on this
information what is the likelihood that an MSM individual would be within the
window to be able to transmit HIV via blood components and we have our answer
choices down below here we’ve got a is one in one-and-a-half million one in
four thousand fifty five which is the correct answer one in three hundred and
fifty seven thousand one in a hundred thousand or one in five hundred and
seven so let’s take a look at this and see what the right answer is and why
that’s the right answer so the thing that you’ve got to realize
is that when someone gets HIV infection there was a period of time of about
twenty-two days until antibodies would show up and then of course you’ve got
antibodies from that point on and then it’s pretty easy to be able to tell
whether the donated blood has HIV in it that’s a no-brainer that’s no problem
the problem was is that if you checked for antibodies within 22 days of the
person getting an HIV infection you would not detect it and you would not
know whether or not this blood was tainted with the HIV virus well go ahead
now and enter in something called na T well na T actually looks for something
different than antibodies remember antibody
are the body’s response to the virus so instead of looking for antibodies we did
something called nucleic acid testing and that brought it all the way down to
nine days what this did was it shortened the window period so in other words now
we could do nucleic acid testing on blood and it would be able to detect far
more infections but we’re still left with this nine day period of time after
an infection whenever it happens that you will not be able to tell whether or
not this blood is tainted with the HIV virus so the question is really what are
the chances that if you use na T testing that you’re gonna spread HIV into the
population because we cannot detect it again what we’re looking at here in the
question is specifically that the window period as we talked about is nine days
that’s nine days out of 365 days the question is is what is the chances of
somebody having HIV during the nine day window period well that’s very simple
it’s simply the chances or the probability of having HIV times the
probability of being during the window period and so what is that well the
chances of having HIV as they said in the MSM population is going to be one
over 100 multiply that by being in the window
period and that’s simply going to be nine divided by 365 this equals nine
divided by three six five zero zero which equals you guessed it one over
forty 55 I hope that answers your question thanks for joining us

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