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.

Patients And 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.

Conclusion: 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.