BCG and PPD

[tiedyeddog]

Hey all, I have a question about the ppd for tb and the bcg vaccine. First aid says bcg can cause a positive ppd while clinical micro made ridiculously simple says it can't. Who's right?

Also, just to clarify, is primary tb always in the lung bases while secondary is always in the apex?

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[Jamiu22]

Hey all, I have a question about the ppd for tb and the bcg vaccine. First aid says bcg can cause a positive ppd while clinical micro made ridiculously simple says it can't. Who's right?

Also, just to clarify, is primary tb always in the lung bases while secondary is always in the apex?

Yes, if you've ever gotten the BCG vaccine, you'll most likely test positive for PPD. I was vaccinated for it... and will always test positive for the PPD skin test, so I just skip the skin test and go straight to the chest x-ray.

And you are right, primary TB is typically at the base of the lung, while reactivation (secondary) TB will arise at the apex (well ventilated region, since mycobactrium TB in a strict aerobe).... the only other time it would be anywhere else is in the case of miliary TB (it can be anywhere, usually in the immunocompromised or those taking TNF-alpha inhibitors)..

 

[tiedyeddog]

Yes, if you've ever gotten the BCG vaccine, you'll most likely test positive for PPD. I was vaccinated for it... and will always test positive for the PPD skin test, so I just skip the skin test and go straight to the chest x-ray.

And you are right, primary TB is typically at the base of the lung, while reactivation (secondary) TB will arise at the apex (well ventilated region, since mycobactrium TB in a strict aerobe).... the only other time it would be anywhere else is in the case of miliary TB (it can be anywhere, usually in the immunocompromised or those taking TNF-alpha inhibitors)..

Just for my own edification, here is a meta analysis saying there isn't a link between the bcg and a positive ppd. http://www.ncbi.nlm.nih.gov/pubmed/7807041

Is it possible many of the people who have had a bcg also have had previous to infection or latent infection given the bcg is only given out in countries where tb is prevalent? I read somewhere, but can't find the link, that bcg is a risk factor for latent tb... I dunno just a thought and this stuff is probably something we will all deal with in the clinics due to how prevalent tb is, so I want to be as well versed as possible in it.

 

[Suncrusher]

Primary TB is wherever the infectious respiratory droplet lands in your lung (which is most often the bases).

 

[tiedyeddog]

Primary TB is wherever the infectious respiratory droplet lands in your lung (which is most often the bases).

Ahh, I couldn't figure out the reason for it. Thanks, it this will help me remember it.

 

[MLT2MT2DO]

First aid says there is, I've had questions on question banks say there is, I have a friend born in India who has had positive PPDs due to the BCG vaccine...

I believe the current literature out there for the correlation between PPD+ and BCG vaccine outweighs the literature against it

 

[Trogghunter]

I had a bcg, my sister got one, my mom got one...neither of us test +. All in healthcare, all <5mm. The bcg vaccinated people who I know who do test positive are Indian, Pakistani. I think that its exposure related. 10-20yrs post bcg, you shouldn't test positive. That is what community health here says, and there are a lot of asian and middle eastern immigrants.

 

[MLT2MT2DO]

I had a bcg, my sister got one, my mom got one...neither of us test +. All in healthcare, all <5mm. The bcg vaccinated people who I know who do test positive are Indian, Pakistani. I think that its exposure related. 10-20yrs post bcg, you shouldn't test positive. That is what community health here says, and there are a lot of asian and middle eastern immigrants.

I believe I also read in a text book sometime during my first two years that <10 yrs +ppd >10yrs -ppd.

For testing purposes I'd be aware that it can cause a +ppd. With that said, a +ppd with negative signs and symptoms and a negative xray doesn't get treated any different if they've had the bcg vaccine or they sniffed an indian girls hair who was TB positive 20 years ago.

 

[tiedyeddog]

I had a bcg, my sister got one, my mom got one...neither of us test +. All in healthcare, all <5mm. The bcg vaccinated people who I know who do test positive are Indian, Pakistani. I think that its exposure related. 10-20yrs post bcg, you shouldn't test positive. That is what community health here says, and there are a lot of asian and middle eastern immigrants.

Uptodates says only 8% of those who received the bcg in childhood are positive in adulthood, so PPD should be given if one hasn't been given before. It also says that a bcg given under ten years ago can result in a ppd greater than 10mm. So I guess the short answer is yes, bcg can cause a positive ppd but not always or even most of the time.

(Just search for bcg on uptodate and then control f for tuberculin skin test)

 

[tiedyeddog]

Thanks everyone!!!! I greatly appreciate it!!