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

[VA Hopeful Dr]

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

One chest x-ray is equal, in terms of radiation exposure, to 3 days of just living on this planet.

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[DrfluffyMD]

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.

I am aware of that. My employers may not be. I was even offered INH once for life long PPD reactivity.

 

[andrek82]

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.

There's got to be regional variation at play. I would have to dig through old papers for the cost breakdown, but where I am it costs 26$ for a PPD including a read at a county TB clinic. That's based on a very thorough cost analysis.

 

[andrek82]

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.

A negative PPD means no TB, but positive leads you down latent vs active TB. Either way you should be treated. In regards to bcg, there is regional variability on age of vaccination, but in general, you should no longer be positive when you're 20 (for infant vaccinations) or 30 (for prepubescent vaccinations such as in China in the mid 90s). IGRA has not been validated in terms of predicting development of active TB in the same way TST has, but those studies are underway, and guidelines are gradually changing to match. From personal experience, the level of evidence needs to be higher to publish a "pro" IGRA paper than one on TST evidence. There is significant distrust of the new assays among some senior TB experts, though they are more and more in the minority.

 

[MedicineZ0Z]

A negative PPD means no TB, but positive leads you down latent vs active TB. Either way you should be treated. In regards to bcg, there is regional variability on age of vaccination, but in general, you should no longer be positive when you're 20 (for infant vaccinations) or 30 (for prepubescent vaccinations such as in China in the mid 90s). IGRA has not been validated in terms of predicting development of active TB in the same way TST has, but those studies are underway, and guidelines are gradually changing to match. From personal experience, the level of evidence needs to be higher to publish a "pro" IGRA paper than one on TST evidence. There is significant distrust of the new assays among some senior TB experts, though they are more and more in the minority.

No you should not. Most (not all) ID docs would pull their hair out over that suggestion. Negative gold = no treatment needed. The PPD simply cannot distinguish the mycobacteria.

Do you know how many positive PPDs we get annually? An insanely high number. And many of whom came from countries and areas with lower TB rates than many parts of USA. Only thing they have in common is the BCG. Also what concrete data is there over the ages you provided?

 

[andrek82]

No you should not. Most (not all) ID docs would pull their hair out over that suggestion. Negative gold = no treatment needed. The PPD simply cannot distinguish the mycobacteria.

Do you know how many positive PPDs we get annually? An insanely high number. And many of whom came from countries and areas with lower TB rates than many parts of USA. Only thing they have in common is the BCG. Also what concrete data is there over the ages you provided?

There are many resources - here is one from the UK only 2 years ago that showed no significant increase in TST response in children over the age of 5 in BCG(+) vs unvaccinated children. (http://thorax.bmj.com/content/thoraxjnl/early/2016/06/22/thoraxjnl-2015-207687.full.pdf) To quote their discussion: " In younger children, BCG did affect TST measurements, but as age increased this effect was less pronounced." The exact ages of 20 and 30 that I quoted are somewhat arbitrary and probably depend on where you train. The general idea is that 15 years between BCG and TST limits false positives to nearly zero.

I never said treat negative IGRA. I specifically stated that IGRA results are being incorporated more and more and are beginning to take precedence, which should be inferred to mean that I would not advocate treating a negative result. However, a positive PPD in a patient without an IGRA and with concern for TB exposure should still be treated. Many public health departments do not have access to IGRA due to funding issues and the majority of their typically under-insured patients can get coverage for INH/rifampin/etc but not the IGRA.

 

[Treebeard]

The guidelines my microbio class taught were "change from negative to positive PPD" and/or "positive PPD of unknown duration". I guess it isn't partixpartic explicit, but that does seem to leave room for vacconv exception IMO.

 

[VA Hopeful Dr]

There's got to be regional variation at play. I would have to dig through old papers for the cost breakdown, but where I am it costs 26$ for a PPD including a read at a county TB clinic. That's based on a very thorough cost analysis.

Likely includes clinic overhead

 

[NotAProgDirector]

The false positive rate for IGRA's is not insignificant. Discussion on the thread suggests that these tests are perfect, which they are not. Because it's a blood test, we tend to "trust" it more than other tests.

Most screening tests are going to demonstrate more false positives than true positives. That's the price we pay for screening.

TB screening is "higher risk" than screening for malignancies, etc, as an infected individual can infect others.

Bottom line: any knee-jerk decision to treat / not treat based upon a single test is silly. A positive TST or IGRA needs to be evaluated based upon the context / patient story. Once an initial CXR excludes active TB, there's no rush to do anything. Sequential testing (TST -> IGRA, or IGRA -> IGRA 6 months later) would be reasonable in low risk patients. Small increases in costs of screening tests can have large financial impacts, although it's important to include all downstream costs (i.e. further testing of false positives) when comparing strategies. Inertia is a huge problem also -- even in the face of a better test / treatment, it's hard to get people / institutions to change.

 

[MedicineZ0Z]

There are many resources - here is one from the UK only 2 years ago that showed no significant increase in TST response in children over the age of 5 in BCG(+) vs unvaccinated children. (http://thorax.bmj.com/content/thoraxjnl/early/2016/06/22/thoraxjnl-2015-207687.full.pdf) To quote their discussion: " In younger children, BCG did affect TST measurements, but as age increased this effect was less pronounced." The exact ages of 20 and 30 that I quoted are somewhat arbitrary and probably depend on where you train. The general idea is that 15 years between BCG and TST limits false positives to nearly zero.

I never said treat negative IGRA. I specifically stated that IGRA results are being incorporated more and more and are beginning to take precedence, which should be inferred to mean that I would not advocate treating a negative result. However, a positive PPD in a patient without an IGRA and with concern for TB exposure should still be treated. Many public health departments do not have access to IGRA due to funding issues and the majority of their typically under-insured patients can get coverage for INH/rifampin/etc but not the IGRA.

The false positive rate for IGRA's is not insignificant. Discussion on the thread suggests that these tests are perfect, which they are not. Because it's a blood test, we tend to "trust" it more than other tests.

Most screening tests are going to demonstrate more false positives than true positives. That's the price we pay for screening.

TB screening is "higher risk" than screening for malignancies, etc, as an infected individual can infect others.

Bottom line: any knee-jerk decision to treat / not treat based upon a single test is silly. A positive TST or IGRA needs to be evaluated based upon the context / patient story. Once an initial CXR excludes active TB, there's no rush to do anything. Sequential testing (TST -> IGRA, or IGRA -> IGRA 6 months later) would be reasonable in low risk patients. Small increases in costs of screening tests can have large financial impacts, although it's important to include all downstream costs (i.e. further testing of false positives) when comparing strategies. Inertia is a huge problem also -- even in the face of a better test / treatment, it's hard to get people / institutions to change.

One important point is that we often assess someone as high risk simply due to their country of origin. Important to be careful with this because of X Y Z countries in one region, X country may not have a significantly high rate of TB at all (relative to USA) but we quickly dismiss it based on the region. Many times a patient lived their whole life in a very low TB area in a higher than average TB rate country too. Details matter.

And of course, the whole nontuberculous mycobacteria which is far more common --> false positive PPD.

 

[evilbooyaa]

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

It's CT scans people worry about in terms of "radiation induced" malignancies. A CXR once a year isn't really a concern.

 

[ekmf27050]

I don't know about "labor intensive", but the fact that my future medical school requires the two-step TB plant and will not accept the quantiferon instead is just bizarre and annoying, in my view.

That's trying to make 4 appointments at my doctor's office, during my work hours. Or, I can pay much higher out of pocket costs to go to a pharmacy or urgent care with more flexible hours. But still, that's four trips instead of just one for the blood test, which is more reliable anyways...

 

[VA Hopeful Dr]

I don't know about "labor intensive", but the fact that my future medical school requires the two-step TB plant and will not accept the quantiferon instead is just bizarre and annoying, in my view.

That's trying to make 4 appointments at my doctor's office, during my work hours. Or, I can pay much higher out of pocket costs to go to a pharmacy or urgent care with more flexible hours. But still, that's four trips instead of just one for the blood test, which is more reliable anyways...

Most urgent cares will place the PPD and read it for $25

 

[kb1900]

I don't know about "labor intensive", but the fact that my future medical school requires the two-step TB plant and will not accept the quantiferon instead is just bizarre and annoying, in my view.

That's trying to make 4 appointments at my doctor's office, during my work hours. Or, I can pay much higher out of pocket costs to go to a pharmacy or urgent care with more flexible hours. But still, that's four trips instead of just one for the blood test, which is more reliable anyways...

Why is it 4 appointments? Is a 2 step different from a ppd where they just inject you day 1 and read day 3?

 

[DocEspana]

No you should not. Most (not all) ID docs would pull their hair out over that suggestion. Negative gold = no treatment needed. The PPD simply cannot distinguish the mycobacteria.

Do you know how many positive PPDs we get annually? An insanely high number. And many of whom came from countries and areas with lower TB rates than many parts of USA. Only thing they have in common is the BCG. Also what concrete data is there over the ages you provided?

They came from st kitts, st lucia, saint martin, monaco, Iceland, the virgin islands or barbados?

The only places with lower rates of TB than the US are isolated islands and... oddly... Monaco.

The US is considered a completely non-endemic area. Aka unless you travel outside the country or are forced into close proximity with someone who got it from outside the country, you cant get TB.

That second component is relevant because we do see that. Its the famous jails and military method of contraction. But... im getting ahead of myself. The point is, realistically speaking, there doesnt exist a place less likely to find a patient with TB than here (excluding very specific isolated islands. And monaco). We arent really getting many immigrants grom those few islands. And what they have in common is not the bcg, its the isolation. Your assumption is sort of off. We got where we are by treating the **** out of our tuberculosis and now we are more or less a tb free country (unfortunately everyone comes to visit and brings their tb with them).

We no longer have any local tb population. And because of that we can back off on the aggressive treatment and use ppd as a screening test where q positive *nearly always* means further testing is needed and not that treatment is needed. The algorithms are based on our previous goal of 'kill it all.' But the interpretation of how to use them is now much more lenient.

 

[DocEspana]

Why is it 4 appointments? Is a 2 step different from a ppd where they just inject you day 1 and read day 3?

Two step means you need a second ppd placed (and read) within a set time frame from the first. Argument is that if you have truly distant, but real, tb history the first ppd may take longer than 48 hours to be positive but that initial exposure to the proteins will make q second one pop positive in a timely manner.

 

[ekmf27050]

Why is it 4 appointments? Is a 2 step different from a ppd where they just inject you day 1 and read day 3?

Two step means you need a second ppd placed (and read) within a set time frame from the first. Argument is that if you have truly distant, but real, tb history the first ppd may take longer than 48 hours to be positive but that initial exposure to the proteins will make q second one pop positive in a timely manner.

Which, given my history of normal one-step PPDs, normal quantiferons, normal chest x-rays, and no TB exposure.... seems a little excessive.

Most urgent cares will place the PPD and read it for $25

My insurance rates jumped way up for any UC visits this year. Even if they didn't, it's still four trips, and $50, instead of a more reliable blood test that my insurance covers in full. I'm not saying schools have to switch and require quant>PPD if they don't want to, but every school should except either/or.

 

[DocEspana]

Which, given my history of normal one-step PPDs, normal quantiferons, normal chest x-rays, and no TB exposure.... seems a little excessive.

My insurance rates jumped way up for any UC visits this year. Even if they didn't, it's still four trips, and $50, instead of a more reliable blood test that my insurance covers in full. I'm not saying schools have to switch and require quant>PPD if they don't want to, but every school should except either/or.

Not that my n=3 is the same as universal law, but are you certain they will charge you for the read visits. I can speak for three different companies (oxford, aetna, cigna) at their mid level insurance coverage levels with three different pcp offices only charging me for the placement visit. The read visits were no copay and not charged to my insurance either.

But yes.... a low risk person has no reason to need a two step ppd.

 

[mehc012]

Not that my n=3 is the same as universal law, but are you certain they will charge you for the read visits. I can speak for three different companies (oxford, aetna, cigna) at their mid level insurance coverage levels with three different pcp offices only charging me for the placement visit. The read visits were no copay and not charged to my insurance either.

But yes.... a low risk person has no reason to need a two step ppd.

No, but 2 times the $25 place/read price posted earlier gives you $50 total.