Significance of Tuberculin Testing in HIV Infection: An Indian Perspective

BackgroundTuberculin skin testing (TST) is a reliable tool in the diagnosis of tuberculous infection and is important in its control. However, it may be false negative in immunocompromised patients like HIV-infected.MethodsWe examined the pattern of TST results in 523 newly diagnosed HIV-positive patients. CD4, CD8 and absolute lymphocyte counts were done by flowcytometry in 63 of these cases.Results56 (44.10%), 15 (11.81%) and 56 (44.10%) of the 127 cases with tuberculosis and 293 (73.99%), 41 (10.35%) and 62 (15.66%) of the 396 cases without any clinical evidence of tuberculosis showed TST results of 0-4, 5-9 and = or > 10 mm respectively. Significantly more (P<0.05) number of cases with TST of = or > 10mm and significantly lesser (P<0.05) number of cases with TST of 0-4 mm are likely to develop tuberculosis. The average CD4+lymphocyte count was found to be significantly lower in cases with nil TST results than with = or >10mm. HIV infected cases associated with tuberculosis with induration on TST had average CD4 counts of 129.5 as compared to 246.3/cmm in those without tuberculosis.ConclusionIn India where both these diseases are endemic, tuberculosis may develop during early HIV infection, while the body's immunity is still largely unimpaired and TST shows = or >10mm results in almost 45% of our cases. In another 45% with TST of 0-4mm, the CD4+ lymphocyte count is likely to be lower than 200/cmm. In those with nil induration, TST of 5-9 mm cannot be taken as an independent marker for suspecting tuberculosis in the HIV infected. Hence we recommend that all cases with TST of = or >10mm and cases with nil induratrion with CD4+ count of <200/cmm should be considered as high-risk for developing tuberculosis.