J Ayub Med Coll Abbottabad;16(2)
PERFORMANCE OF ICT-TB TEST in the Detection of Pulmonary and
extra-Pulmonary TUBERCULOSIS
Department
of Pulmonology, Ayub Teaching Hospital Abbottabad, *LRH
INTRODUCTION
Tuberculosis (TB) still
ranks as one of the major diseases and is a leading killer of mankind.1 Currently
a large number of our population is infected with Mycobacterium Tuberculosis
and is at the risk of developing the disease.2 It is a major public
health problem in Pakistan.
The diagnosis of
tuberculosis depends upon a number of tests such as Chest X-ray, acid fast
bacilli (AFB) stain and culture of sputum. These conventional methods are not
satisfactory because sputum AFB stain is less sensitive and AFB culture takes
more than 3 weeks to produce results.3 More sensitive and specific
tests such as Polymerase Chain reaction (PCR) are too expensive for routine
laboratory diagnosis of TB.
The recently
introduced serological test ICT-TB rapidly detects antibodies in the serum
of pulmonary & extra pulmonary TB
patients. It is said to be a reliable test to make an early diagnosis of TB.
MATERIAL AND METHODS
The study was conducted
during the period from January 1998 to Dec 2002 at the Department of Pulmonology, Ayub Teaching Hospital Abbottabad and LRH Peshawar
with the collaboration of Department of Pathology, Khyber Medical College
Peshawar.
A total of 129
patients were selected from the patients who had been hospitalized in the Pulmonology unit of Lady Reading Hospital Peshawar and Ayub
Teaching Hospital Abbottabad.
The control group
consisted of 25 non TB patients or healthy subjects who showed no evidence of
TB on Chest X-Ray and AFB Stains.
The sera were
separated and ICT was performed according to the manufacturer’s manual. Briefly
30 ml of serum and three drops of reagent consisting of antihuman IgG coated particles were applied to each side of the
membrane, enabling reactions to takes place between the membrance fixed antigens and antibodies in the serum
followed by antibody-antihuman IgG complex formation produc-ing one or more pink lines with in 15 minutes. The
test was positive if the control band was observed and one or more positive
bands were seen. The specificity and sensitivity were calculated.
The percentage of patients
and control subjects who showed positive antibody response are
given in Figure 1.
The assay
detected 44% (23 of 52) of sputum positive cases, 36% (11 of 30) of smear
negative pulmonary TB, 20% (10 of 30 patients) of TB Pleural effusion and 35%
(6 of 17) of TB Lympadenitis patients. None of the
control subjects had positive ICT-T.B. The sensitivity for smear positive
pulmonary TB was 44%. It was 36% for TB smear negative Pulmonary TB, 20% for TB
Pleural effusion & 36% for TB Lymphadenitis. Specificity was 100% as all the
control subjects showed Negative ICT. TB.
Figure
1: Percentage of Pul & Extra Pul T.B. patients
with positive antibody response along with non T.B. patients.
Tuberculosis is the major public
health problem in
Chang et al found
the diagnostic sensitivity of ICT-TB as 73% and specificity in the range of
88-4%.3 Other studies found that tests using the 38 KDA antigen had
a sensitivity of 92% for sputum positive. 70% for sputum negative patient and
76% for extra-pulmonary tuberculosis while the overall specificity was 92%.4
Our study gave a
specificity of 100% almost similar to the studies conducted so far, while the
sensitivity in our study was 44% for smear positive patients, 36% for smear
negative Pulmonary T.B, 20% for TB Pleural effusion & 35% for Tuberculous lymphadenitis. The sensitivity is low as
compared to other studies due to the reason that some people show poor antibody
production due to genetic variations & differences in study populations.5-7
We conclude that ICT test is highly specific but less sensitive test for diagnosis of tuberculosis, however in conjunction with other diagnostic techniques, it may serve as a valuable aid in clinical diagnosis for both Pulmonary and extra pulmonary TB. Further larger trials are needed for its evaluation.
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