Impact of peripheral lymphocyte count on the sensitivity of 2 IFN-gamma release assays, QFT-G and ELISPOT, in patients with pulmonary tuberculosis.
OBJECTIVE
This study evaluated the effect of peripheral lymphocyte count on 2 interferon-gamma release assays [QuantiFERON TB-Gold (QFT-G) and enzyme-linked immunospot (ELISPOT)] and their sensitivity in patients with pulmonary tuberculosis, including HIV-negative immunocompromised patients.


METHODS
Two hundred thirty patients with microbiologically confirmed active pulmonary tuberculosis were subjected to the tests. Lymphocyte counts were analyzed simultaneously.


RESULTS
Overall sensitivity was 74% (159/215; 95% CI, 68-80%) for QFT-G and 92% (198/215; 89-96%) for ELISPOT (p<0.0001). In patients with peripheral lymphocyte counts of > or =1000/microL, sensitivity was high for both QFT-G (88%, 111/126; 82-94%) and ELISPOT (97%, 122/126; 94-100%). However, the sensitivity decreased significantly with decreasing peripheral lymphocyte count for both QFT-G (test for trend p<0.0001) and ELISPOT (test for trend p=0.007). When lymphocyte counts were <500/microL, the sensitivity was 81% (25/31; 66-96%) for ELISPOT, but only 39% (12/31; 21-57%) for QFT-G.


CONCLUSIONS
Both QFT-G and ELISPOT are sensitive methods for detecting active pulmonary tuberculosis, but their sensitivity partly depends on peripheral lymphocyte counts. At low lymphocyte count conditions, ELISPOT is superior to QFT-G for detecting tuberculosis, irrespective of age, gender, and nutrition.
Komiya
Kosaku
K
Department of Pulmonary Medicine, Tokyo National Hospital, Tokyo, Japan. komiyakh1@yahoo.co.jp
Ariga
Haruyuki
H
Nagai
Hideaki
H
Teramoto
Shinji
S
Kurashima
Atsuyuki
A
Shoji
Syunsuke
S
Nakajima
Yutsuki
Y
D000368:Aged; D015897:Comorbidity; D015986:Confounding Factors, Epidemiologic; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D018023:HIV Seronegativity; D006801:Humans; D016867:Immunocompromised Host; D007371:Interferon-gamma / Q000378:metabolism*; D018655:Lymphocyte Count; D008231:Lymphopenia / Q000150:complications; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D014397:Tuberculosis, Pulmonary / Q000097:blood* / Q000276:immunology
D007371:Interferon-gamma