Korean J Lab Med.  2010 Aug;30(4):414-419. 10.3343/kjlm.2010.30.4.414.

Analysis of Patients with Positive Acid-fast Bacilli Culture and Negative T-SPOT.TB Results

• Han YM
• Kim HS
• Kim CH
• Kang HJ
• Lee KM

• KMID: 1781649
• DOI: http://doi.org/10.3343/kjlm.2010.30.4.414

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.

Keyword

Tuberculosis; Interferon-gamma; Nontuberculous mycobacteria; T-SPOT.TB; False negative

MeSH Terms

Adult
Aged
Aged, 80 and over
Bacillus/*isolation & purification
Culture Media
Female
Humans
Lymphocyte Count
Lymphopenia/diagnosis/microbiology
Male
Polymerase Chain Reaction
Reagent Kits, Diagnostic
Sensitivity and Specificity
Tuberculosis/*diagnosis/microbiology/radiography

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