Limitations of the QuantiFERON®-TB Gold test in detecting Mycobacterium tuberculosis infection in immunocompromised patients
Article Outline
- Abstract
- 1. Introduction
- 2. Case reports
- 3. Discussion
- 4. Learning point
- 5. Competing interest statement
- References
- Copyright
Abstract
Four cases are presented, immunosuppressed by at least three different mechanisms: one HIV-positive patient with a CD4 count of 0.29
×106/ml, one malnourished patient, and two kidney-transplanted patients. All patients had a negative interferon (IFN)-γ test for suspected tuberculosis (TB), but a positive culture. We conclude that a negative IFN-γ test does not exclude TB disease in immunosuppressed patients.
Keywords: Tuberculosis antigen test, Immunodeficiency, Diagnostic, Specificity, Sensitivity
1. Introduction
Tuberculosis (TB) infects 15 to 20 million people worldwide, of whom approximately 8 million develop active disease annually [1]. In developed countries, TB commonly affects older individuals, ethnic migrants, and individuals with human immunodeficiency virus (HIV) infection. Isolation of Mycobacterium tuberculosis by culture is the definitive diagnostic test. The tuberculin skin test (TST) is useful for proving infection, but not necessarily disease. A positive test only suggests prior exposure to the antigen, not active infection. If the patient is in an immunosupressed state, a negative test does not rule out TB infection.
In 2005, a new in vitro test, QuantiFERON®-TB Gold (QFT; Cellestis, Carnegie, Australia), was introduced as an aid for diagnosing M. tuberculosis infection, including both latent infection and TB disease. The test has operational advantages over the tuberculin test because results can be available 24 hours after testing, no return visit is required, and repeated testing does not cause boosting [2]. Furthermore, the QFT test is significantly more specific than the skin test, and data suggest that it also may be more sensitive [3]. Information on the test in immunocompromised individuals is limited and a warning is attached to the test instruction. The present report describes four patients with active TB disease and impaired immune function of various etiologies and with negative QFT tests. One patient reverted to become responsive during antituberculous (anti-TB) treatment.
2. Case reports
2.1. Case 1
A 62-year-old male kidney-transplanted patient of Indian origin was admitted to the hospital in June 2004 because of fever. The patient had a history of arterial hypertension and type 2 diabetes mellitus (DM) since the age of 44. He was diagnosed with end-stage renal disease (ESRD) and on hemodialysis since 2001 until a cadaveric renal transplantation was performed in 2003. He experienced an uncomplicated post-transplantation period with no rejection episodes. Immunosuppressive treatment included steroids, mycophenolate mofetil (MMF), and cyclosporine. He was investigated extensively and epithelioid granulomas were found in bone marrow aspiration. LP was performed and cerebrospinal fluid analysis tested positive for PCR-TB complex. Acid-fast bacillus (AFB) microscopy was negative, but growth of M. tuberculosis was obtained later. The patient fully recovered without sequelae. Analyses with IFN-γ assay in late July and September tested negative.
2.2. Case 2
A 62-year-old female of Danish origin, HIV-positive since 1995 and under antiretroviral treatment since 1997, was admitted in June 2004 because of 3 months of loose stools, night sweats, weight loss, coughing, and tiredness. Expectorated sputum was found inconclusive for PCR-TB and anti-TB medication was initiated for a short period. After termination of anti-TB medication, renewed examinations were initiated and a computed tomography (CT) scan of the abdomen showed necrotizing, retroperitoneal lymph node enlargement, histopathologically consistent with TB, but negative AFB microscopy. A chest radiograph was normal. TST was negative, but anti-TB treatment was initiated again in August. In October 2004, because of slowly increasing lower back pain and no decrease in C-reactive protein concentration, a CT scan of the lumbar column was performed and showed a 4×7×14 cm abscess involving the right psoas muscle. Biopsy and drainage of abscess material showed AFB on microscopy and was PCR-TB-positive. An IFN-γ assay in August was negative. Her immune status was only moderately depressed with a CD4 count of 0.29×106/ml and a fully suppressed HIV-RNA viral load. She survived without sequelae.
2.3. Case 3
A 58-year-old male, born in Greenland but living in Denmark for the past 30 years, was admitted in June 2005 following 3 months of a general diseased condition with significant weight loss, anorexia, fatigue, and productive cough. He was a smoker and had a history of alcohol abuse. BMI on admission was 14 kg/m2 and he had a plasma albumin level of 20 g/l. A chest radiograph showed diffuse right-sided infiltrates and pneumothorax on the left side. A sputum smear was AFB-positive. TST was 6 mm. An anti-TB regimen was initiated but had to be withheld for short periods due to hepatic toxicity. His general condition, as well as his nutritional status, never really improved despite enteral and parenteral nutritional supplements. The patient died after 5 months of TB treatment. IFN-γ assay was negative on admission but reverted to positive after 3 months of treatment.
2.4. Case 4
A 54-year-old female of Pakistani origin and living in Denmark was admitted to the hospital in 2004 due to uremia. The patient had a history of type 2 DM since the age of 52, hypertension, and was diagnosed with diabetic nephropathy and ESRD in 2005. In addition, she had hepatitis C infection. A cadaveric renal transplantation was performed in October 2005. Immunosuppressive treatment consisted of cyclosporine, MMF, and steroids. The post-transplantation course was complicated by recurrent bacterial infection, which was treated with antibiotics. A chest X-ray in March 2006 showed diffuse nodular infiltrates. In May, the patient developed pain and tenderness of the lower extremities. Magnetic resonance imaging showed bilateral necrosis of the head of the femora but no abscess.
The patient was treated empirically with broad-spectrum antibiotics until culture of gastric lavage fluid, and later direct microscopy of pus from an abscess at the femora, revealed AFB. Also, CSF was PCR-TB-positive. An anti-TB regimen was initiated. The patient survived. IFN-γ assay in June tested inconclusive and negative in July.
3. Discussion
The QFT test has been introduced as an improvement in the diagnosis of TB. The present case series demonstrates that severe, active M. tuberculosis infection may be associated with a negative QFT test in patients with impaired immune function due to immunosuppressive therapy, HIV infection, or malnutrition. Previously, a negative QFT test was reported in post-transplant M. tuberculosis infection following liver transplantation [4]. This is a limitation of the test since TB is more difficult to detect in immunosuppressed patients.
The QFT test is based on the detection of IFN-γ released by T cells in response to M. tuberculosis-specific antigens. The test uses two proteins encoded by a unique genomic segment that is present in M. tuberculosis. These proteins, ESAT-6 and CFP10, are major targets for IFN-γ-secreting T lymphocytes in M. tuberculosis-infected individuals. Patient response to the ESAT-6 antigen is reported to be 60–80% [5] and almost the same for the CFP10 antigen [6]. Specific anergy observed in our patients may be caused by different mechanisms–pharmacological immunosuppression, HIV-infection, and the poorly defined immunosuppression observed in malnourished patients–and interpretation of this response in terms of diagnosis and M. tuberculosis infection should be cautious. Further studies in clinical settings are required to identify immunological correlates that may predict when the test is reliable.
4. Learning point
5. Competing interest statement
“Mads Hornum, Klaus Leth Mortensen and Anne-Lise Kamper declare that they have no conflict of interests”.
“Åse Bengård Andersen is co-inventor of a patent regarding the use of ESAT-6 as a diagnostic reagent. The Statens Serum Institut, Copenhagen, Denmark holds royalties related to this discovery.”
References
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- . Guidelines for using the QuantiFERON-TB Gold test for detecting Mycobacterium tuberculosis infection, United States. MMWR Recomm Rep. 2005;54(RR–15):49–55
- Specific detection of tuberculosis infection: an interferon-gamma-based assay using new antigens. Am J Respir Crit Care Med. 2004;170(1):59–64
- Posttransplant Mycobacterium tuberculosis disease following liver transplantation and the need for cautious evaluation of Quantiferon TB GOLD results in the transplant setting: a case report. Transplant Proc. 2006;38(4):1083–1085
- Differential T cell responses to Mycobacterium tuberculosis ESAT6 in tuberculosis patients and healthy donors. Eur J Immunol. 1998;28(12):3949–3958
- . Diagnosis of tuberculosis based on the two specific antigens ESAT-6 and CFP10. Clin Diagn Lab Immunol. 2000;7(2):155–160
PII: S0953-6205(07)00237-3
doi:10.1016/j.ejim.2007.03.020
© 2007 European Federation of Internal Medicine. Published by Elsevier Inc. All rights reserved.
