CD4-TEST AS SURVIVAL PREDICTORS IN PULMONARY TUBERCULOSIS HIV-INFECTED PATIENTS( LYMPHOCYTES AND TUBERCULIN SKIN)

Background We analyse whether the tuberculin skin test is a good survi val marker in a cohort of pulmonary tuberculosis patients with HIV inf ection (PTB/HIV). In all, 494 PTB/HIV patients were enrolled in Barcel ona (Spain) between January 1992 and December 1994 in the Tuberculosis Program of Barcelona. The main data problem was the large proportion of missing values in the covariates percentage of T CD4+ lymphocytes a nd the tuberculin test results: only 157 patients (31.8%) had both cov ariates recorded. Methods Patients were dichotomized into two groups a ccording to their level of immunosuppression (less than or equal to 14 and >14% T CD4+ cells). First, we carried out the semiparametric and parametric complete case analysis. After this, we analysed the data as suming a missing at random non-response pattern. We developed a bootst rap approach where missing data in the markers are imputed via a two-w ay linear model. Using Weibull regression estimation, we used a multip le imputation scheme to estimate the parameters of interest. Results W e found significative differences for the most immunosuppressed group when comparing positive tuberculin patients with those who were tuberc ulin negative. From a complete case approach and through a multivariat e Cox analysis, we obtained a significant relative hazard of 0.3657 (9 5% CI: 0.13-1.02; P = 0.054). When a Weibull model was fitted, we esti mated a constant relative percentile value of pR = 4.1329 (95% CI: 0.9 7-17.59). From a missing data approach, we obtain a higher constant re lative percentile 5.48 (P = 0.079). Conclusions The imputation method allows us to assess the protective character of positivity for the tub erculin test for the lowest CD4+ level. These findings strongly sugges t the value of the tuberculin skin test as a qualitative measure of th e immunological response and its interest for developing countries whe re specific laboratory tests are not affordable.