[Analysis of patients with positive acid-fast bacilli culture and negative T-SPOT.TB results].
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.
Han
You Mie
YM
Department of Radiology, Hallym University College of Medicine, Seoul, Korea.
Kim
Hyun Soo
HS
Kim
Cheol Hong
CH
Kang
Hee Jung
HJ
Lee
Kyu Man
KM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001407:Bacillus / Q000302:isolation & purification*; D003470:Culture Media; D005260:Female; D006801:Humans; D018655:Lymphocyte Count; D008231:Lymphopenia / Q000175:diagnosis / Q000382:microbiology; D008297:Male; D016133:Polymerase Chain Reaction; D011859:Radiography; D011933:Reagent Kits, Diagnostic; D012680:Sensitivity and Specificity; D014376:Tuberculosis / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000382:microbiology
D003470:Culture Media; D011933:Reagent Kits, Diagnostic