Conversion of QuantiFERON-TB Gold Plus following Isoniazid Prophylaxis among Latent Tuberculosis Patients

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Sawang Saenghirunvattana, MD
Chitchamai Siangproh, BSc
Natsuda Wongkhot, BSc
Chonticha Noomcharoen, RN
Paulet Barro Ortiz, RN


OBJECTIVES: To evaluate the conversion of QuantiFERON-TB Gold plus (QFT-Plus) following Isoniazid prophylaxis among latent tuberculosis (LTB) patient.

MATERIAL AND METHODS: We conducted a case series starting in December 2016 up to the present March 2019. Twenty asymptomatic cases were identified to have had exposure to active tuberculosis (TB) infection, undergone chest x-ray and QFT-Plus test. Those with positive test QFT-Plus results with negative chest x-ray reports were prescribed with Isoniazid 300mg tablet once daily for nine months. Post prophylaxis, chest x-ray and QFT-Plus were repeated to determine the conversion results.

RESULT: All 20 participants were QFT-Plus test positive and chest x-ray negative. The average age was 47 ± 5.7 years and there were eighteen females and two males. Two had underlying conditions: valvular heart disease and peripheral neuropathy. All took the nine-month Isoniazid prophylaxis and repeated the QFT-Plus test and chest x-ray. Chest x-ray results again were all negative. Eighteen cases revealed persistence of positive QFT-Plus and two cases were negative. The initial conversion rate of QFT-Plus post treatment (2017) was ten percent. In the succeeding years (2018 and 2019), another ten percent conversion was reported and sixteen cases maintained their positive baseline score.

CONCLUSION: To our knowledge this clinical series is the first to report 20% conversion rate of QFT-Plus among LTB participants prescribed with a nine-month Isoniazid prophylaxis. This study only evaluated the conversion of QFT-Plus with LTB participants being treated with 9-month Isoniazid. As there is no gold standard on the definition and distinction of conversion and reversion, further studies are warranted to optimize the correlation between the efficacy of varied latent tuberculosis infection (LTBI) and TB treatment regimen and conversion of QFT-Plus results.


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Saenghirunvattana S, Siangproh C, Wongkhot N, Noomcharoen C, Ortiz PB. Conversion of QuantiFERON-TB Gold Plus following Isoniazid Prophylaxis among Latent Tuberculosis Patients. BKK Med J [Internet]. 2019 Oct. 24 [cited 2023 Dec. 10];15(2):145. Available from:
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