TB testing strategies lack positive predictive value in HIV+ of India
Various testing approaches including chest x-ray and cough for at least 2 weeks lacked positive predictive value and specificity in determining which symptomatic but ambulatory HIV patients had pulmonary tuberculosis in Chennai and Pune, India.
Revised Indian national guidelines base TB diagnosis on
sputum smear and response to a course of antibiotics. World
Health Organization guidelines call for early chest x-ray of
HIV-positive people with TB symptoms. Researchers at the
National Institute for Research in Tuberculosis in Chennai
conducted this analysis of initial chest x-ray in various TB
diagnostic algorithms in symptomatic HIV-positive people with
negative sputum smears.
The study involved 504 adults, 330 of them (65%) men. Age
averaged 35 years and median CD4 count stood at 175
cells/µL. All study participants had cough or fever for
at least 2 weeks and three sputum smears negative for
acid-fast bacilli. All were ambulatory.
Chest x-ray had a sensitivity of 72% and a specificity of 57%
in diagnosing sputum culture-confirmed pulmonary TB.
(Sensitivity is the ability of a test to single out people who
have a certain disease. Specificity is the ability of the test
to classify people who do not have the disease as negative.)
Chest x-ray had a positive predictive value of only 21% and a
negative predictive value of 93% in diagnosing
culture-confirmed TB.
TB culture was positive for TB in 49 of 235 people (21%) with
an abnormal initial chest x-ray and in 19 of 269 (7%) with a
normal initial chest x-ray, a highly significant difference
(P < 0.001).
Cough for 2 or more weeks had a sensitivity of 97% in
diagnosing culture-confirmed pulmonary TB but a specificity of
only 6%. Positive predictive value of cough was 14% and
negative predictive value 94%. Absense of weight loss had a
high negative predictive value.
Although an initial chest x-ray is moderately sensitive in
diagnosing pulmonary TB, the authors conclude that relying on
initial x-ray leads to overdiagnosis. None of the algorithms
tested had a good positive predictive value for identifying
culture-confirmed pulmonary TB.
The researchers stress that “a rapid and accurate
diagnostic test is required for HIV-infected chest
symptomatic” patients.
Source: Chandrasekaran
Padmapriyadarsini, Srikanth Tripathy, Lakshmanan Sekar,
Perumal Kannabiran Bhavani, Nitin Gaikwad, Srinivasan
Annadurai, Gopalan Narendran, Nagamiah Selvakumar, Arun R.
Risbud, Dinesh Sheta, Sikhamani Rajasekaran, Aleyamma Thomas,
Fraser Wares, Soumya Swaminathan. Evaluation of a diagnostic
algorithm for sputum smear-negative pulmonary tuberculosis in
HIV-infected adults. JAIDS. 2013; 63: 331-33.
For the study abstract
(Downloading the complete article requires a
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abstract is
free.)
Source:
IAS
