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Journal of Clinical Microbiology, December 1999, p. 4201-4201, Vol. 37, No. 12
0095-1137/99/$04.00+0
LETTERS TO THE EDITOR
Field Evaluation of Rapid Tests for Tuberculosis Diagnosis
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LETTER |
We read with great interest the letter previously published
by M. P. Grobusch et al. (1). Evaluation of
diagnostic tests is indeed a topical problem, especially in developing
countries. We agree with the authors' remark that the rapid test
(AMRAD/ICT) could be considered only as an adjunct test
to standard techniques of tuberculosis (TB) diagnosis. However, we
would like to comment on the last conclusion drawn by the authors. The
reported study was realized in a European hospital, and the specificity
observed was very good. This would not be always the case in developing countries, particularly in tropical areas where people are permanently in contact with various pathogens and develop cross-reacting antibodies responsible for poor specificity. Therefore, it is important that every
new test and, particularly, every new serodiagnostic assay be validated
with the controls of the country where the test will be applied.
Furthermore the low sensitivity of the AMRAD/ICT assay (50%) will
result in false-negative results for many patients. Thus, although the
specificity is excellent, the negative predictive value of the test
will be unacceptably low even in countries with a high prevalence of
TB. Therefore, we do not believe that such a test would be suitable as
a first-line method of diagnosis. Sputum smear microscopy has been
proven to be very useful for diagnosis of contagious TB cases in
developing countries where diagnostic tools such as radiology are
missing. Still, a serological test for the diagnosis of
paucibacillary and extrapulmonary TB would be of interest if it
were more sensitive and faster and could be used on large series of
samples. Also, keep in mind that serodiagnostic tests necessitate blood
sample collection and disposable materials that are not readily
available in most countries with a high prevalence of human
immunodeficiency virus or hepatitis. In resource-poor areas, all these
factors have to be taken into account when evaluating the efficacy and
cost of a rapid test.
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FOOTNOTES |
*
Phone: 261 20 22 401 64 Fax: 261 20 22 41534 E-mail: vrasolof@pasteur.mg
| |
REFERENCE |
| 1.
|
Grobusch, M. P.,
D. Schürmann,
S. Schwenke,
D. Teichmann, and E. Klein.
1998.
Rapid immunochromatographic assay for diagnosis of tuberculosis.
J. Clin. Microbiol.
36:3443[Free Full Text].
|
| | | | |
Voahangy Rasolofo*
|
| | | | |
Suzanne Chanteau
Tuberculosis Unit, Pasteur Institute
P.O. Box 1274
101 Antananarivo, Madagascar
|
| |
AUTHOR'S REPLY |
We thank Drs. Rasolofo and Chanteau for their thoughtful comments on
our previously published work (4). It is obvious from the
data published so far that we are aware of (1, 4, 6) that
the sensitivity and specificity of the test vary with the region where
it is used. We understand that when one ponders the possible use of
this rapid immunochromatographic antigen detection assay for TB
diagnosis in a certain world region, its significance in terms of high
positive and negative predictive values has to be judged on the basis
of sensitivity and specificity data obtained in pilot trials in that
particular setting in comparison to locally used standard methods.
As stated in our letter, we conclude that the currently available assay
as presently applied cannot be considered an ultimate breakthough in
the serodiagnosis of TB, particularly in countries where reliable
diagnostic tools are available regardless of costs. However, we do not
share Rasolofo's and Chanteau's belief that the use of this assay in
certain settings as a first-line diagnostic tool should be dismissed on
the grounds of these data.
At present, TB diagnosis in developing countries relies largely on
clinical features, X ray, and microscopy of acid-fast sputum stains.
Cultivation as the diagnostic "gold standard" is a costly (and
therefore not ubiquitously available) and complex technique, requiring
up to several weeks before a definite diagnosis is established (1). By using serodiagnostic methods, the time required for reaching a clinical decision to treat a suspected case of tuberculosis can be drastically reduced, as in some cases the actual proof of an
organism's identity does not depend on its isolation or identification
in a specific culture (3). At present, serodiagnosis is a
rapid technique that is technically facile, can be automated, and, if
in routine use, is inexpensive. The technique is also usable for
diagnosing nonpulmonary TB and is particularly attractive for the
identification of TB manifestations in which specimens are not easily
accessible, e.g., skeletal TB.
Serodiagnosis in its current form carries a potential which is not
entirely sounded so far, particularly if, as hypothesized earlier, the assay detecting human antibody response to the
38-kDa antigen indicates mycobacterial disease requiring
treatment in the immunocompetent patient rather than tuberculosis sensu
strictu (5). We would therefore like to underline again that
this simple technique and its attractive price appear to make it
particularly interesting for use in developing countries
(2).
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REFERENCES |
| 1.
|
Cole, R. A.,
H. M. Lu,
Y. Z. Shi,
J. Wang,
T. De-Hua, and A. T. Zhou.
1996.
Clinical evaluation of a rapid immunochromatographic assay based on the 38 kDa antigen of Mycobacterium tuberculosis on patients with pulmonary tuberculosis in China.
Tuber. Lung Dis.
77:363-368[Medline].
|
| 2.
|
Daniel, T. M.
1989.
Rapid diagnosis of tuberculosis: laboratory techniques applicable in developing countries.
Rev. Infect. Dis.
11(Suppl. 2):S471-S478.
|
| 3.
|
Good, R. C., and T. D. Mastro.
1989.
The modern mycobacteriology laboratory. How it can help the clinician.
Clin. Chest Med.
10:315-322[Medline].
|
| 4.
|
Grobusch, M. P.,
D. Schürmann,
S. Schwenke,
D. Teichmann, and E. Klein.
1998.
Rapid immunochromatographic assay for diagnosis of tuberculosis.
J. Clin. Microbiol.
36:3443.
|
| 5.
|
Grobusch, M. P.
1999.
Rapid immunochromatographic assay for diagnosis of tuberculosis: antibodies detected may not be specific.
J. Clin. Microbiol.
37:2112. [Author's reply.]
|
| 6.
|
Zhou, A. T.,
W.-L. Ma,
P.-Y. Zhang, and R. A. Cole.
1996.
Detection of pulmonary and extrapulmonary tuberculosis patients with the 38-kilodalton antigen from Mycobacterium tuberculosis in a rapid membrane-based assay.
Clin. Diagn. Lab. Immunol.
3:337-341[Abstract].
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| | | | |
Martin P. Grobusch
Medical Clinic (Infectious Diseases)
Charité/Campus Virchow Hospital
Humboldt University
Augustenburger Platz 1
13353 Berlin, Germany
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Journal of Clinical Microbiology, December 1999, p. 4201-4201, Vol. 37, No. 12
0095-1137/99/$04.00+0
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