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Old 03-24-2015
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Default PPD test and sarcoidosis

can someone explain what is the relationship between a negative PPD and sarcoidosis?

does it mean a negative PPD result could mean a possibility of sarcoidosis disease?
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Old 03-24-2015
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PPD is for TB, it's when we use a TB antigen and then wait for a Delayed Type 4 Hypersensitivity Reaction (Th1-CD4) to occur. If it's negative that mean's the patient doesn't have TB (It's a screening test NOT used in USA)

Sarcoidosis also causes the same kind of reaction in tissues it targets (primarily the lung) which is called "Granulomatous Reaction".

PPD causes a granulomatous reaction and so does sarcoidosis in effected organs.

That's the only connection I can think of.
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Originally Posted by spasemaster View Post
PPD is for TB, it's when we use a TB antigen and then wait for a Delayed Type 4 Hypersensitivity Reaction (Th1-CD4) to occur. If it's negative that mean's the patient doesn't have TB (It's a screening test NOT used in USA)

Sarcoidosis also causes the same kind of reaction in tissues it targets (primarily the lung) which is called "Granulomatous Reaction".

PPD causes a granulomatous reaction and so does sarcoidosis in effected organs.

That's the only connection I can think of.
I agree with you, these points I don't doubt at all.
FA mentions that PPD- if no infection or anergic (steroids, malnutrition, immunocompromise) and in sarcoidosis. So I am just wondering what would a negative test for PPD mean with respect to sarcoidosis.
Could we 100% say that a PPD- result mean we have a +ve sarcoidosis disease?
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Ahaaaaaaaaa,
In Goljan it says that CD4 Th cells in sarcoidosis can interact with other Antigens. One of those antigens is Mycobacterial KatG protein.
So, a POSITIVE (false positive that is)PPD in a NON-TB patient could mean sarcoidosis due to the cross reactivity.


I have to add that commonly a PPD test might also be false negative in a patient with sarcoidosis along with TB infection due to the impaired immunity!
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Last edited by spasemaster; 03-24-2015 at 08:40 AM. Reason: Extra info on the topic
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Ahaaaaaaaaa,
In Goljan it says that CD4 Th cells in sarcoidosis can interact with other Antigens. One of those antigens is Mycobacterial KatG protein.
So, a POSITIVE (false positive that is)PPD in a NON-TB patient could mean sarcoidosis due to the cross reactivity.

But also a positive PPD could mean latent TB, right? so, we cant definitely rule out TB? we would need further test to exclude either one?

So from your explanation, if PPD is +ve, I could be facing sarcoidosis (due to false positive), so whenever I have sarcoidosis I will get +ve result for PPD but in-fact TB is not actually present (so realistically the result is negative)

Have I gotten my understanding right?
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Yes, so in a POSITIVE PPD in a sarcoidosis patient:
-False positive (More common) due to the crossover and the imparired immunity.
-True positive due to latent TB

Negative PPD in a sarcoidosis patient:
-False negative due to the impaired immunity
-True negative
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