[MCOH-EH] Possible false positive quantiferon TB

[Swift, Melanie D., M.D., M.P.H.]

Hi Michael, It is recommended to repeat a positive IGRA in a low-risk individual. Usually, it will be negative on retest. If it's persistently positive, interpret it considering how many tubes are positive, the absolute IFN-G value and a detailed history. If both tubes are positive, they’re from a country with medium or high TB rates, have a concerning travel history, spent time in other high-risk environments, or have a condition increasing their risk for TB progression, I would assume it's a true positive and recommend LTBI treatment.

I have seen a couple of healthy US-born individuals who have never traveled out of the country and are positive in QTF tube TB-2. They had nothing happening in tube 1, a great positive mitogen control, and no exposure risk or risks for TB progression. I suspected a false positive and they did turn negative on retesting with another QTF after 3 months. You could also do a 2 step TST if you needed quicker resolution.

But of course there are no concerns for them working in the meantime with a negative CXR and no symptoms.
Hope this helps,
Melanie
________________________________
From: MCOH-EH <mcoh-eh-bounces+swift.melanie=mayo.edu at mylist.net> on behalf of Band, Michael DO <MBand at watsonclinic.com>
Sent: Friday, November 10, 2023 6:57:12 AM
To: mcoh-eh at mylist.net <mcoh-eh at mylist.net>
Subject: [EXTERNAL] [MCOH-EH] Possible false positive quantiferon TB

How are your institutions handling positive quantiferon test in asymptomatic nonexposed, prior negative skin test employees?

False positive rates can be high in low incidence cohort.

Chest xray negative

Michael Band DO,MS
Watson Clinic



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