Annals of Laboratory Medicine

Korean Society for Laboratory Medicine (대한진단검사의학회)
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Analysis of Patients with Positive Acid-fast Bacilli Culture and Negative T-SPOT.TB Results

  • Han, You-Mie (Department of Radiology, Hallym University College of Medicine) ;
  • Kim, Hyun-Soo (Department of Laboratory Medicine, Hallym University College of Medicine) ;
  • Kim, Cheol-Hong (Department of Internal Medicine, Hallym University College of Medicine) ;
  • Kang, Hee-Jung (Department of Laboratory Medicine, Hallym University College of Medicine) ;
  • Lee, Kyu-Man (Department of Laboratory Medicine, Hallym University College of Medicine)
  • Received : 2010.04.24
  • Accepted : 2010.07.20
  • Published : 2010.08.31
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Abstract

Background : T-SPOT.TB is a sensitive test that detects interferon-gamma producing T-cells in tuberculosis patients following stimulation with tuberculosis-specific antigens. Our study was aimed to investigate the possible causes of false negative results of the test by analyzing the patients with positive acid-fast bacilli (AFB) culture and negative T-SPOT.TB results. Methods : We investigated 138 patients with positive AFB culture results reported between January 2009 and April 2010. Medical records of these patients were reviewed for the results of T-SPOT.TB test, AFB culture, PCR for Mycobacterium tuberculosis (TB-PCR), chest X-ray, drug treatment, etc. Diagnosis of tuberculosis was confirmed by positive TB-PCR or identification of Mycobacterium tuberculosis (MTB). Sensitivity of T-SPOT.TB test was calculated and the possible causes of AFB culture positive and T-SPOT.TB negative results were analyzed. Results : T-SPOT.TB test was performed in 63 of the 138 patients with AFB culture positive results. Fifty-six (88.9%) were positive and 7 patients (11.1%) were negative on T-SPOT.TB test. Of these 7 negative cases, 4 were confirmed as nontuberculous mycobacteria (NTM), 2 were suspected as NTM and diagnosis could not be confirmed in 1. Six of these 7 patients were over 70 yr old and 6 patients had lymphocytopenia. T-SPOT.TB negative results were not observed in any of the 44 patients confirmed to have active tuberculosis (sensitivity 100%). Conclusions : Our results suggest that T-SPOT.TB test is very sensitive for diagnosing active tuberculosis. NTM may be the main cause of AFB culture positive and T-SPOT.TB negative results, but MTB infection in immunocompromised patients also has to be considered.

배경 : 결핵 진단용 T-SPOT.TB 검사는 환자의 림프구를 결핵균특이항원으로 자극하여 인터페론감마가 분비되는지를 확인하는, 민감도가 높은 검사이다. 본 연구에서는 항산균 배양양성이면서 T-SPOT.TB 음성인 경우를 분석하여 어떤 환자에서 위음성으로 나타나는지 확인하고자 하였다. 방법 : 2009년 1월에서 2010년 4월 사이에 항산균 배양 양성인 138명의 환자를 대상으로 T-SPOT.TB 검사, 항산균 배양, TB-PCR, 흉부 X선, 결핵 치료 등에 관한 의무기록을 조사하였다. 항산균 배양 양성이면서 TB-PCR 양성이거나 결핵균으로 동정된 경우 결핵으로 확진하였다. T-SPOT.TB 검사의 민감도를 구하였고, 항산균 배양 양성이면서 T-SPOT.TB 음성인 경우는 원인을 분석하였다. 결과 : 총 138명의 항산균 배양 양성 환자 중 63명의 환자에서 T-SPOT.TB 검사가 시행되었다. T-SPOT.TB 검사 양성이 56명(88.9%)이었고 음성이 7명(11.1%)이었는데 음성 7명 중 4명은 비결핵항산균(NTM)으로 확인되었고 2명은 NTM이 의심되었으며 나머지 1명은 확인되지 않았다. 또 7명 중 6명이 70세 이상의 노인 환자였으며, 6명은 림프구수가 감소되어 있었다. 활동성 결핵으로 확진된 44명 중 T-SPOT.TB 음성인 경우는 한 건도 없었다(민감도 100%). 결론 : 본 연구 결과에서 활동성 결핵 진단을 위한 T-SPOT.TB 검사의 민감도가 매우 높았으며, 항산균 배양 양성이면서 T-SPOT. TB 음성인 경우는 NTM인 경우가 많겠지만 면역억제에 의한 MTB 감염 또한 고려해야 할 것으로 생각되었다.

Keywords

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