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

You Mie Han; Hyun Soo Kim; Cheol Hong Kim; Hee Jung Kang; Kyu Man Lee

doi:10.3343/kjlm.2010.30.4.414

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Han, Kim, Kim, Kang, and Lee: Analysis of Patients with Positive Acid-fast Bacilli Culture and Negative T-SPOT.TB Results

Original Article

Korean J Leg Med 2010;30(4):414-419.

Published online: 14 January 2010

DOI: https://doi.org/10.3343/kjlm.2010.30.4.414

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

You Mie Han, M.D.¹, Hyun Soo Kim, M.D.², Cheol Hong Kim, M.D.³, Hee Jung Kang, M.D.², Kyu Man Lee, M.D.²

¹Departments of Radiology, Seoul, Korea

²Laboratory Medicine, Seoul, Korea

³Internal Medicine, Hallym University College of Medicine, Seoul, Korea

Corresponding author: Hyun Soo Kim, M.D. Department of Laboratory Medicine, Hallym University College of Medicine, 94-200 Yeongdeungpo-dong, Yeongdeungpo-gu, Seoul 150-719, Korea Tel: +82-2-2639-5562, Fax: +82-2-2671-5270 E-mail: hskim0901@empal.com

Revised 24 April 201015 July 2010 Accepted 20 July 2010

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Keywords: Tuberculosis, Interferon-gamma, Nontuberculous mycobacteria, T-SPOT.TB, False negative

REFERENCES

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Table 1.

AFB culture positive patients (N=138)

Group	N of patients
TB confirmed
T-SPOT.TB positive	44
T-SPOT.TB negative	0
T-SPOT.TB, not tested	31
NTM confirmed
T-SPOT.TB positive	1
T-SPOT.TB negative	4
T-SPOT.TB, not tested	3
Unconfirmed AFB culture positive
T-SPOT.TB positive	11
T-SPOT.TB negative	3
T-SPOT.TB, not tested	41
Total	138

Abbreviations: TB, tuberculosis; NTM, nontuberculous mycobacterium; AFB, acid fast bacilli.

Table 2.

Clinical findings of patients with AFB culture positive and T-SPOT.TB negative results

Patient No.	Age/sex	Specimen	AFB smear	AFB culture	TB-PCR	T-SPOT. TB	X-ray CT	Leukocyte count (/uL)	Lymphocyte count (/uL)	Underlying disease	Tb Tx	TB/NTM confirmed
1	78/M	Sputum	-/-/-	+/+/-	-	-	Chronic destructive lung, traction bronchiectasis, TB or NTM, probable stabilized	14,600	600	COPD, past TB history, AMI	ND, death	NTM (Mycobacterium spp.)
2	24/M	Sputum	-/-/-	-/-/+	-	-	Consolidation, infected bullae pneumonia or TB (NTM)	7,590	740	Pneumonia	Done, improved	NTM (M. fortuitum complex)
3	71/F	BW	1+/-	+/+	-/-	-	Nodule, bronchiectasis TB or NTM, probable stabilized	7,800	800	Old CVA, cough, past TB history	Done, improved	NTM
4	72/M	Sputum	3+/1+/1	+ +/+	-/-	-	Cavitary, consolidation, nodules TB or NTM, probable active	9,530	2,270	Burn, pneumonia	Done, not improved	Unconfirmed NTM probable
5	82/M	BW	-	+	-	-	Patchy consolidation, nodules TB or NTM, undetermined activity	9,880	740	Cholecystitis, pneumonia	ND	Unconfirmed
6	93/F	Sputum	-/-/-	-/+/-	-	-	Pulmonary fibrosis, consolidation R/O pneumonia	6,670	890	Congestive heart failure	ND	Unconfirmed
7	79/M	Sputum	-/-/-	-/+/-	-	-	Consolidation lobar pneumonia	17,200	516	Pneumonia	ND	NTM (M. fortuitum complex)

Abbreviations: AFB, acid-fast bacilli; TB, tuberculosis; NTM, nontuberculous mycobacterium; COPD, chronic obstructive pulmonary disease; AMI, acute myocardial infarction; ND, not done; BW, bronchial washing; CVA, cerebro-vascular accident.

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