Voiceover: Let's say you plant a
PPD and a person comes back in, and now they want to find out
whether it's positive or negative. The way I kind of think about it is I break people down into their risk group. I think of 3 risk groups. I think high risk, medium
risk, and low risk. If they're not high or medium, then they basically by
default become low risk. That's how it works out. Going to the high risk, there's
2 ways to think about it. Either I'm really worried that
they are going to have TB, and that could be someone
who I suspect has it, maybe they have a very
abnormal chest x-ray, or maybe they lots of fevers, cough, night sweats, things like
that and I really suspect TB. They would fall in the high risk, right? Because I worry that they have it. In fact, even their family
members, close contacts, let's say a grandchild
of a person who has TB, or and uncle or an auntie
of somebody who has TB, someone in the household, they are also at high risk of getting TB. These are folks I'm worried
may have tuberculosis, but also in this high risk group I'm going to put a third group, or a third category which is immunocompromised people. This is people that do not have a normal immune system so these folks it's not that I'm worried that
they have TB necessarily, but it's that if they did have TB, gosh, that would be really
awful because tuberculosis requires that you have
a good immune system, and if they don't have
a good immune system then tuberculosis is going to be devasting for these folks especially folks with HIV. In this first group then,
the high risk group, either I'm really worried
that they have it, or I'm worried that if they did get it they would get really sick with it. For these folks, a positive test would be induration, remember in PPD
you're measuring induration anything above 5 millimeters, anything above this range
would be considered positive. For example, if someone with HIV comes and they have a PPD of,
let's say, 6 millimeters then they would definitely be positive, but if it was 3, then
they would be negative. This red stuff that
I'm kind of filling in, this is the positive range,
positive anywhere in here. Anything below that, I'm
going to write it in white down here. This would be
negative, anything below 5. If it's exactly 5, then
that's still positive. Who's in the medium range? These folks. One group would be people
coming from an endemic country. Let's say they recently came across from China or parts of Africa. If they're coming from a country where tuberculosis is very common or endemic, then they are also in
that medium risk group. Also folks that live or
work in large groups. Think about nursing homes, or let's say, a jail or an army barracks. Anyone that lives or works in these kinds of places in a large group setting, I'll say large group setting, is
at risk for getting TB because, of course, it spreads from
person to person very quickly. If you're around a lot of people,
you're upping your chances. Similarly, people that are in health care so anyone working in a
hospital setting because, of course, people with TB
often come to health care settings to be take care of. If you're in a health care setting working as a nurse or a doctor, then
you also are in the medium risk. I, myself, because I'm a physician, am in the medium risk for this reason. I'll put a few more up here; IV drug use. This also puts you in the medium risk. Then I'm going to actually switch gears, and just as before where
I said I'm also worried, specifically worried about certain groups, here I'm very worried about
children less than 4 years of age. If you're less than 4 years of age meaning if you're 3, or 2, or 1, those children they may
not have any other reason for getting TB like the
people I just mentioned like health care setting
or endemic country where it's around, but if they did get it, it would be particularly
problematic because young kids don't have
great immune systems. Also, people that are actually
fighting other diseases. We call those comorbidities. Let's say you have
already gotten a disease like diabetes, or let's say your
kidneys aren't working properly, if you already have other diseases then you're also at risk
because if you did get TB, it would be even tougher to fight it off. For all of these folks, 10 millimeters or above is considered positive. I didn't make an exhaustive list. There actually are a few other ones, but I tried to highlight some of the most important ones on this list. For example, just to
make sure we understand how to utilize this, let's
say you have a person who is 3 years old and
that person comes in with a PPD of 12 millimeters. That would be positive here, but
if it was only 8 millimeters, it would be negative so that's
how you would use this graph. So down here then we have anyone else, anyone that doesn't fit
into the other categories fits into this final one so
this is the low risk category. For these folks, 15 millimeters
or greater are needed to be considered positive. If you have someone that is very healthy, and doesn't fit into
any of the other things that we just talked about and
their PPD is 20 millimeters, then they would be considered positive, but if it was only,
let's say, 13 millimeters somewhere in this other range down here, then they would be considered negative. You basically measure the induration, and then you kind of think
about what risk group a person falls into; high, medium, or low, and then you kind of organize
it using these graphs, very easy, right? So above 5, or above 10, or above 15 tells you which is considered positive versus negative. A couple of questions people
always ask is they think, "What if someone falls into
2 of these categories?" What if they're, let's
say, below 4 years old, let's say we're talking about a 3 year old so they have this one, but
you're also really worried that they have TB so they're in this one. If you ever have someone
that falls into 2 categories, you have to go with the
more conservative approach, and say if they meet
the high risk category, I'm going to use that
one to decide if they're positive or negative. In this case, a 3 year
old who I suspect has TB automatically I would have
to go with this top one because I suspect TB simple as that. The other question that often
comes up is what about BCG vaccine? This is a vaccine that
some countries offer to their citizens to
help prevent disseminated or spreadout TB especially a
problem among young babies. What if someone has had BCG vaccine? It's very clear. The
Centers for Disease Control has been very clear on this point. They say, "You do not
need to interpret the PPD "with this in mind. Ignore
the BCG vaccine completely." In other words, when
you're trying to figure out whether someone's PPD
is positive or negative, just rely on the high,
medium, and low risk criteria that we've talked about. Do not worry about the BCG vaccine. That should not affect your decision.