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Latent Tuberculosis



Hey, whats going on guys?  And welcome to another video.  Today, were going to talk about latent tuberculosis and how we do the workup and treatment for those diagnosed with latent tuberculosis.  Alright, so, lets get started here.  Now, the first thing that we need to address is, who are we going to test?  Were not going to test everyone, this is not universal screening.  We’re only testing in a few and specific populations.  Now, were going to test those patients who are at risk for infection, at risk for reactivation of tuberculosis, and those who are actually going to benefit from the treatment.  These are the only indications for doing routine screening for latent tuberculosis.  Now, by definition, latent tuberculosis means that we do not have any symptoms.  So, these are asymptomatic patients that we are administering these tests to.

Now, how are we going to do this?  Well, we have two ways.  We can do it through PPD or we can do it through something called interferon gamma release assay.  Now, by far the most common way of testing latent tuberculosis is going to be through PPD.  So, what were going to do is administer the PPD, were going to have the patient come back in about 2-3 days, so 48-72 hour period, and were going to check to make sure that it is positive, or we are going to check to make sure it is negative.  Now, a positive reading is based on induration; very important.  So, erythema has no significance whatsoever.  So, it doesn’t matter how red it is, we are actually measuring the edema or the induration that the PPD left.  Thats what is being measured, and thats what gives a positive test.  Now, its very important to also note that BCG vaccination if done in other countries can influence this test, but we disregard that.  So, who cares if they have had prior BCG vaccination, we don’t take that into account.  We are looking for induration regardless.  Now, also, you need to be aware that if this is the first time they are having a PPD placed you can get a false negative.  So, what you are going to do is your going to have to repeat this test once again, and if it comes back negative, then they have a true negative.  If it comes back positive, then now you have an actual positive for latent tuberculosis, and you need to continue the workup for that.  So, be aware, the first time a PPDis given, it can give a false negative.

Alright, so like I said, were going to measure induration.  Now, how much induration is considered positive?  It depends on your risk factors.  So, if you have 5mm of induration or more and you have HIV, live with somebody that has TB, you have some kind of immunosuppression, or you have a chest x-ray that is consistent with healed tuberculosis; 5 mm of induration is considered positive.  Patients that are recent immigrants (usually within the past 5 years), drug use, health care workers, prisoners, have malignancy, or have diabetes, a positive test for these patients is considered to be 10 mm of induration.  Now, 15 mm is considered positive for anybody that doesn’t have any type of risk factors.  So, this is going to be the majority of the population; 15 mm gives you a positive test.

So, now what?  We have a positive tuberculosis screening.  The next step in management is going to be to order a chest x-ray.  Were going to order the chest x-ray to exclude active infection.  Like I stated earlier, if you have a suspicion for active infection, you will not do these screening.  You need to go straight to chest x-ray and you need to go straight to culture and smears of the sputum.  So, this is for asymptomatic individuals.  You do a chest x-ray to exclude active infection, and if they don’t have active infection, the next step is to treat for latent tuberculosis.

How are we going to treat these patients?  Were going to give INH for nine months.  INH has this side effect thats called peripheral neuropathy and it affects vitamin B6 metabolism.  So, for that reason, everybody that is being given INH should also be given vitamin B6, pyridoxine.  This is to prevent the peripheral neuropathy that is associated with isoniazid.  Its not very common, however, it is a preventable adverse reaction to the medication.  So, just be aware you need to give everyone vitamin B6.  Treat everyone with INH for nine months.  This is going to reduce the risk of having active infection later on down the road.  Alright guys, thanks so much.  This was a little quick overview on latent tuberculosis.