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.
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Source: IAS