Interpreting the PPD

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 and I think of three risk groups I think high risk medium risk and low risk and if they're not higher medium then basically they kind of by default become low risk that's how it works out so going to the high risk there's two ways to think about it right 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 you know very abnormal chest x-ray or maybe they have lots of fevers coughs you know 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 and in fact even their family members close contact so let's say a grandchild of a person who has TB or an uncle or auntie of somebody who has TB someone in the household they are also at high risk of getting TB so 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 so 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 devastating for these folks especially folks with HIV so in this first group then the high-risk group either I'm really worried they have it or I'm worried that if they did get it they would get really sick with it and for these folks a positive test would be in duration remember PPD you're measuring in duration anything above five millimeters anything above this range would be considered positive so for example if someone with HIV comes and they have a PPD of let's say six millimeters then they would definitely be positive but if it was three then they would be negative so this red stuff that I'm kind of filling in this is the positive range positive anywhere in here and anything below that I'm going to write it in white on here this would be negative so anything below five and if it's exactly five then that's still positive so 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 you know 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 so 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 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 and 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 taken care of and so if you're in a health care setting working as a nurse or a doctor then you also are in the medium risk and I myself because I'm a physician and in the medium risk for this reason I'll put a few more up here IV drug use this also puts you in a medium risk and then let me actually switch gears and just as before where I said well I'm also worried specifically worried about certain groups here I'm very worried about children less than four years of age so if you're less than four years of age meaning if you're three or two or one those children they may not have any other reason for getting TB like the people I just mentioned like health care setting or an 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 and also people that are actually fighting other diseases so we call those comorbidities let's say you have already gotten a disease like diabetes or let's say your your your kidneys aren't working properly if you already have other diseases then you're also a risk because if you did get TV it would be even tougher to fight it off and for all of these folks ten millimeters or above is considered positive I didn't make an exhaustive list or actually are a few other ones but try to highlight some of the most important ones on this list and for example then 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 well that would be positive here but if it was only 8 millimeters it would be negative so that's kind of 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 and for these folks 15 millimeters or greater are needed to be considered positive and so if you have someone that let's say 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 so you basically measure the in duration 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 about 15 tells you which is considered positive versus negative and a couple of questions people always ask is they think well what if someone falls into two of these categories what if their let's say a below 4 years old let's say we're talking about a 3 year old so they're you know have this one but you're also really worried that they have TB so they're in this one well if you ever have someone that falls into two categories you have to go with the more conservative approach and say well if they meet the high-risk category I'm going to use that one to decide if they're positive or negative so in this case a three year old - our suspect has TB automatically I would have to go with this top one because I suspect TB simple as that and the other question often comes up is what about BCG vaccine this is a vaccine that some countries offer to their citizens to help prevent disseminated or spread out TB especially a problem among young babies so what if someone has had BCG vaccine and 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