Significance of Tuberculin Testing in HIV Infection: An Indian Perspective

Tuberculin 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.

We 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.

56 (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.

In 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.