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Why do we still use the PPD? And give liver toxic drugs because of it?

Discussion in 'Medical Students - MD' started by MedicineZ0Z, Apr 16, 2018.

  1. MedicineZ0Z

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    To step foot in a hospital, you need a PPD. But why? We have a vastly superior test (the Quantiferon) for one. But also, the PPD is a pretty crappy test given its complications.

    We have the BCG cohort who all seem to magically have gotten TB and should be handed a liver toxic drug because their PPD vaguely read 1mm over debatable cutoffs. Anyone who isn't an ID doc seems to strongly defend whereas the ID docs will point out the high risk of false positives.

    My point being, why can't we switch over to the Quantiferon if we're so fixated on TB screening?
     
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  3. shisong

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    i do not know much but at the root of it is MONEY... im guessing.. maybe Quantiferon cost lot of money in comparison to PPD?
     
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  4. Goro

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    PPD is NOT labor and resource intensive.
     
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  5. Oso

    Oso

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    Quantiferon is hella expensive and not always covered by insurance (mine, for example). PPD is cheap and a good enough screening test for those without a significant exposure history

    Again, PPD is a screening test, not diagnostic. It’s not like if your PPD read is positive they just send you home on multiple drugz
     
  6. studentdocftw

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    All positive ppd indicates is a need for CXR. It's not like we treat every positive ppd...and it's cheaper than the blood test and I'm pretty sure the sensitivity/specificity profiles of both are close enough to warrant the continued use of the ppd. Otherwise, id assume they would've already been phased out.
     
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  7. MedicineZ0Z

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    A positive PPD can get you INH.
     
  8. Foot Fetish

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    I think this depends on the institution. I had the BCG vaccine as a kid, so I have a positive PPD. So far, I've only had to provide negative quantiferon results, not even a CXR. I would flat out refuse to take INH if they told me to. This is actually something I'm worried about. Do they check trough levels of INH or something? If I was forced to fill the prescription, I would just throw it in the trash and pretend I took it. I know I don't have TB, so I'm not gonna subject myself to potentially harmful drugs for no reason.
     
    #7 Foot Fetish, Apr 16, 2018
    Last edited: Apr 18, 2018
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  9. Doctorows

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    I had to take INH as a teenager after a single positive PPD (15mm exactly) followed by a negative CXR.
     
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  10. shisong

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    wait really?

    I had BCG when i was young so i always have + PPD, but after quantiferon gold + CXR. They said i dont need anything else
     
  11. ortnakas

    ortnakas OMS-IV

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    Quantiferon negative and CXR negative should spare you isoniazid based on every protocol I’ve ever heard of.
     
  12. MedicineZ0Z

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    Well you explained my point quite well. It's nonsense.
    Protocol = INH after positive PPD. You can take the quantiferon but it isn't something that's automatically ordered.
    We're causing so much more harm via a liver toxic drug due to this nonsense belief that BCG won't cause a false positive PPD. It's ridiculous.
     
  13. ndafife

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    This is far from a standard protocol everywhere
     
  14. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    The 2016 IDSA guidelines suggest confirmatory testing before treatment
     
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  15. kb1900

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    I have never heard of giving INH after a positive PPD without a follow up cxr or quant. Though I did have to pay for an uncovered expensive cxr due to an improperly read PPD once.
     
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  17. NITRAS

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    If you have latent TB, and you refuse to take isoniazid, you will limit your job opportunities.

    A PPD does not diagnose TB. It is a great screening tool.
     
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  18. ndafife

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    Also literally everyone knows BCG causes a false positive PPD. That's why the recommendation is for people with the vaccine to get the quantiferon.
     
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  19. Mad Jack

    Mad Jack Critically Caring
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    No one will get INH for a positive PPD alone lol, that being prescribed for a positive PPD is irresponsible bordering on malpractice
     
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  20. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    Off topic, but for future reference find a free-standing imaging center and offer to pay cash up front.

    In my area, doing so will get you a chest x-ray and the read for $35
     
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  21. pawprint

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    This is a great question that I have received different answers on from multiple Infectious Disease doctors I have worked with.

    My own personal story: I tested positive on my first PPD in undergrad, was told I had latent TB and I needed a chest x-ray, which was negative. I was not started on any medication. A couple years later when starting medical school, I received another PPD and had an even bigger spot on my arm than the first time (>15mm). I was again given a chest xray and not started on any medication. About a year later, during an Infectious Disease lecture taught by one of my institutions practicing ID docs, she stated during her presentation that my positive PPD indicated I had latent TB and she would advise I go on INH therapy. So I went and saw my PCP, who performed a quantiferon gold which showed I had absolutely no prior infection with TB. Meaning I did not have latent TB. So I was not started on medication. A few months later I was working with a different infectious disease doctor who agreed that because my PPD was positive but the quantiferon gold was negative, it means I am negative for latent TB and I don't need INH.

    Long story short, I had one ID doctor who wanted to treat me with INH for the positive PPD, and another who said the quantiferon gold was the better test and to trust that over the PPD. The problem that rises from this is that every time I have to go to a new clinical site and show records of my PPD, somebody always freaks out over my positive PPD and makes me redo a quantiferon gold (no matter how recent it is) and sends the results to an ID doctor to ask them their opinion on my situation. There was one period during my clerkships where I had 3 quantiferon gold tests over 3 months (all of which were completely negative).

    People obviously have no idea what to do with a positive PPD anymore. Its a crappy screening test that causes people to react inappropriately. People are still taught or at least living with the mindset that positive PPD = latent TB, which is not true. Every new place I go that asks for a PPD screen I have to tell them I have to get the quantiferon gold anyway. I'm all for the quantiferon gold replacing the PPD for everyone.
     
  22. BigRedBeta

    BigRedBeta Why am I in a handbasket?
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    The last two hospital systems I've accepted a paycheck from have switched to Quantiferon testing. Will accept a recent PPD if it's been done, but explicitly stated their preference is for the Quantiferon
     
  23. y123

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    I got prescribed INH after positive PPD with negative X-ray too many many years ago. I knew nothing about INH or PPD back then. My doctor did not even mention Quantiferon.
     
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  24. MedicineZ0Z

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    Not true...
     
  25. Mad Jack

    Mad Jack Critically Caring
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    I suppose I should have specified "prescribing treatment based on a PPD alone without evidence of active disease and without ensuring informed consent of the patient by explaining the risks and benefits of treatment" is borderline to actual malpractice, as treatment is considered optional for those without active infection and has substantial risks. Informed consent is the cornerstone of medicine
     
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  26. Perrotfish

    Perrotfish Has an MD in Horribleness
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    'Latent TB' is a positive PPD or quantiferon without evidence of active infection on CXR, which includes a normal CXR. Treatment of latent TB reduces the rate of progression to active TB by 80% and is recommended by, to the best if if knowledge, all the US ID societies. The CXR is to confirm ACTIVE TB, which requires multi drug therapy. You don't need to go through an informed consent for treatment of latent TB any more than you do when ordering abx for PNA.

    The IDSA and Pediatric red book do disagree on the relative merits of a TST vs quantiferon, with the IDSA recommending a quantiferon for pretty much everyone and the red book only recommending it for previous BCG vaccination. The IDSA also recommends a confirmatory test (second TST or quantiferon) after a positive PPD, while the rest book does not have as clear a recommendation. Mostly, though, they agree
     
    #24 Perrotfish, Apr 17, 2018
    Last edited: Apr 17, 2018
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  27. Mad Jack

    Mad Jack Critically Caring
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    The lifetime risk of conversion to active TB is 10%, hence why treatment is a recommendation, not a requirement, and anything that is a recommendation requires informed consent. A good number of RTs I worked with eventually developed a positive PPD after enough years of practice, but I can't think of a single one that got treatment. They all just got their yearly CXRs at employee health and monitored for symptoms. Don't know a single one that converted to active TB (yet) despite some being positive for 20+ years.

    So to the op, you don't want to take that hit to your liver, you don't have to, but that decision is yours to make with the knowledge that you're putting yourself at risk for quarantine down the line. If there is a health system out there that requires treatment, I've never come across it, but it's a big county and some places will fire you for vaping or not getting a flu shot so I guess I wouldn't be surprised.
     
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  28. pawprint

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    I think the OP's overall point is that the PPD is a bad test to begin with when compared to the quantiferon gold. The PPD is prone to user error (the nurse could be reading erythema instead of induration), along with the actual reading of the test being influenced by subjective lifestyle factors of the patient. Also there are false positives due to skin reactions to the test (such as myself).

    The Quantiferon gold tests your blood directly for a response of your immune system to TB antigens, without the influence of easily mistaking erythema for induration or lifestyle factors. You either have a response or you don't. Its a better test and we won't be giving people INH therapy for a PPD that may not represent a person's TB exposure accurately.
     
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  29. kb1900

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    Unbelievable wow. I was charged $170. I literally got scammed.
     
  30. Mad Jack

    Mad Jack Critically Caring
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    That was also kind of my initial point- they'd confirm with a CXR and/or quantiferon first, but then we got sidetracked
     
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  31. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    Yes but the quanterferon test is very pricey and hard to draw/prep. TST is super easy and a decent screening test
     
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  32. Perrotfish

    Perrotfish Has an MD in Horribleness
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    Again:
    1) CXR is not a confirmatory test for latent TB. Its a test for active TB. If you have a positive PPD and a completely normal Xray you need to recommend treatment for latent TB

    2) If you choose to follow the new, controversial, and very weak 2016 IDSA guideline for a confirmatory test for a positive PPD prior to beginning treatment they recommend a confirmatory... PPD. They just want to show that test is positive twice before starting treatment. They don't recommend any additional testing for diagnosis unless you have a clear hx of the BCG vaccine.
     
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  33. qxrt

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    What's ******ed is that my residency hospital requires Quantiferon test but doesn't accept PPD, but my fellowship hospital requires PPD but doesn't accept Quantiferon as part of the onboarding process. I mean, cost is one thing, but now I have to get both to make both hospitals happy in the interim. Why the **** would a hospital refuse a Quantiferon result that I already have in favor of a PPD? And I'm talking big ivory-tower institutions here, not some small podunk hospital with wonky policies. How ******ed is that? Some ass-backwards policies around here. I seriously want to drag the morons who came up with this policy out of their positions and instill some people with common sense in their place.

    Apologies for the above, but seeing this thread just made me have to vent about ridiculous, stupid policies in healthcare.
     
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  34. Perrotfish

    Perrotfish Has an MD in Horribleness
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    That is profoundly stupid.
     
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  35. CherryRedDracul

    CherryRedDracul The Sunlight Burns
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    Sooner or later, everyone of you will realize a lot of administrators aren't quite the sharpest knives in the drawer.
     
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  36. MedicineZ0Z

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    And common sense says do the Quantiferon. If you're going to potentially cause harm... you better be sure the person has the disease.
    No one should be doing INH without a Quant. unless they're at very high risk (ex. prison population in 3rd world country).
    Lol I've seen this too. One place not accepting one or the other.
     
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  37. MedicineZ0Z

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    How is it decent? Compare the actual TB rate vs. the PPD positive rate.
     
  38. Mad Jack

    Mad Jack Critically Caring
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    If the organization themselves is doing a quant, it is $12/test, versus $3 for a PPD in materials. It's not a huge difference. If they're sending them out it's $50-100 for a quant, $25-50 for a PPD. The math is pretty variable, but if it's a hospital with their own everything a quant is pretty cheap. I can see an argument that goes either way depending on how the costs break down for an individual organization
     
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  39. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    That's not even close to true. Cheapest I've ever seen a quant was $50. A 10 dose vial of PPD is $80, so $8 each. And that's my price, I bet a hospital can do better.
     
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  40. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    If you follow the guidelines it's pretty good.

    Also, how often does INH actually cause liver damage.

    Show your work for both, since this is your claim that we're causing loads of unneeded liver damage.
     
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  41. Mad Jack

    Mad Jack Critically Caring
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    My bad, it was some nonsense I found on Google. Here's an actual study.
    Cost analysis of tuberculin skin test and the QuantiFERON-TB Gold In-tube test for tuberculosis screening in a correctional setting in Dallas, Texas, USA

    Total cost per test was $25.97 per PPD, $44.96 per Quantiferon Gold, including staffing needs and everything related to the tests.
     
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  42. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    I once again call BS.

    $8 per dose. $1 per syringe.

    CMAs go for $15/hr in my area. Let's say your CMA is slow and can only do 6 TSTs/hour. Labor cost is then $3 for 2 visits.
     
  43. MedicineZ0Z

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    Guidelines say BCG history doesn't change your plan and you proceed with INH. Never understood the rationale behind that... I mean, surely we don't think all these immigrants in health care have TB right? Most aren't even from countries/areas with high rates of TB and the BCG vaccine was given due to slightly higher rates decades ago.

    My point with INH is, we don't need to give someone something that's potentially harmful when there's likely no reason to give it at all. Being on the safe side is a good argument when we have no better choice. In this case, the quantiferon gold is the much better choice. But not all places/guidelines/protocols recognize that and still go positive PPD --> INH.

    We can take notes from this and apply it to other aspects of screening that have a hard time catching up. Ex. Better tests out there for prostate cancer (ex. isoPSA) that can guide towards a biopsy with better precision.
     
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  44. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    So you've got no evidence behind what you say.

    Got it.
     
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  45. pawprint

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    INH causes mild liver toxicity in about 20% of patients who take it (mild meaning subclinical but a noted rise in AST/ALT), about 1% actually experience sustained liver damage and 0.1% experience liver failure. This info is from uptodate which gets this info from some older studies...so not sure how accurate that is.

    Either way, I think the take away is that positive PPD no longer means starting someone on INH like it used to. The new emerging protocol according to the IDSA guidelines is as follows:

    PPD --> Quantiferon --> INH

    However, many places are still alarmed at the positive PPD's and think people need x-rays and treatment after the first PPD comes back positive. Replacing the PPD all together with the quantiferon would be nice because it would bypass the confusion positive PPD's currently cause. Although, I do understand the difference in cost, and lab tech's have to be trained on how to draw the quantiferon specifically.
     
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  46. DrfluffyMD

    DrfluffyMD Probationary Status

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    I always had positive PPD, no hx of TB, and just opted out INH everytime and opted for CXR.

    Negative quantiferon
     
  47. MedicineZ0Z

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    The amazing evidence that has such insane inconsistency from one hospital to the next?
     
  48. VA Hopeful Dr

    VA Hopeful Dr Senior Member
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    Plenty of doctors don't stay current. Why does it surprise you that some of them end up running employee health?
     
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  49. Psai

    Psai Account on Hold
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    Man op what year of medical school are you? Your understanding of tb screening is inadequate for an ms2 and above.
     
  50. MedicineZ0Z

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    And why is that? We use negative PPDs to rule out TB and positive TBs to investigate further (chest xray). My issue is with BCG vaccine history being ignored along with the Quantiferon not being widely used. Along with the INH recommendations.
     
  51. Giovanotto

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    Hmm, what about chest x-ray exposure over a life-time?
     
  52. pawprint

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    If you had a negative quantiferon then you don't need chest xrays. You likely have a skin reaction to the PPD, negative quantiferon means your white blood cells have never seen TB mycobacterium in your body before.
     

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