While blood tests have a higher specificity, the sensitivity is pretty similar between PPD and IGRAs.
I researched this a while back as the numbers differ between CDC estimates and the test manufacturers.
Where CDC estimates differ from the manufacturer’s package insert I have indicated it:
Melanie Swift, MD
Director, Vanderbilt Occupational Health Clinic
From: MCOH-EH [mailto:mcoh-eh-bounces+kdayvault11=att.net@mylist.net]
On Behalf Of Morelli, Karen J
Sent: Wednesday, July 30, 2014 2:07 PM
To: 'MCOH/EH'
Subject: [Bulk] Re: [MCOH-EH] Quantiferon gold TB test - preplacement question
I assume you meant to type that the Quantiferon is positive now after a negative ppd one month ago. I have been monitoring the Quantiferon issue since we had a cluster of false positives last fall (presumably
due to tube/process issues). The research I have done states that Quantiferon could be run within a 3 day window of receiving a ppd, after that there is a chance of getting a false positive reading on the Quantiferon (from the ppd plant). There is no concrete
“cut off” time frame that I have seen to know when it would be okay to run a Quantiferon after a ppd. The TB expert in my area stated that false positive Quantiferon tests have been noted up to 6 weeks after a ppd. Due to the uncertainty of when it would
be okay to run a Quantiferon after a ppd, our department has adopted a 6 months cut off time.
Thank you,
Karen Morelli RN, BSN
Eastern Maine Healthcare Systems
From: MCOH-EH [mailto:mcoh-eh-bounces@mylist.net]
On Behalf Of Band, Michael DO
Sent: Wednesday, July 30, 2014 1:41 PM
To: mcoh-eh@mylist.net
Subject: [MCOH-EH] Quantiferon gold TB test - preplacement question
Currently we are using the quantiferon gold TB test for use after a positive ppd for preplacement.
Every once in a while a new doctor or employee are not available for a 48-72 hour ppd read so we do quantiferon instead.
Had a new doctor with a negative ppd one month ago at another facility and her quantiferon gold is negative.
NO symptoms of active TB and no known exposures. She is in a low risk specialty for TB exposure.
Chest xay normal
Question:
1.
I read somewhere that a recent ppd can interfere with the quantiferon gold test. Not sure if this is true?
2.
What is the next step? Do we call this latent Tb? Is it worth repeating the quantiferon gold test? Could this be a false positive?
Thanks for any help.
Michael Band DO, MS
Watson Clinic
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