Objective: To determine whether the total lymphocyte count (TLC) accurately predicts a low absolute CD4+ T-cell count and CD4+ percentage in persons infected with human immunodeficiency virus (HIV).
Design: Retrospective analysis of data collected in the US Air Force HIV Natural History Study.
Setting: Military medical center that performs annual medical evaluation of all HIV-infected US Air Force personnel.
Patients: A total of 828 consecutive patients with no prior history of zidovudine use, evaluated from January 1985 through July 1991. For patients with multiple observations over time, a single data point within each 6-month interval was included in the analysis (N = 2866).
Measurements and main results: The sensitivity, specificity, and likelihood ratio (LR) of the TLC, in the range of 1.00 x 10(9)/L to 2.00 x 10(9)/L, in predicting an absolute CD4+ T-cell count less than 0.20 x 10(9)/L or a CD4+ percentage less than 20% were calculated. In addition, the LR and pretest probability of significant immunosuppression were used to calculate posttest probabilities of a low CD4+ count for a given TLC value. The LR of the TLC in predicting an absolute CD4+ count < 0.20 x 10(9)/L increased from 2.4 (95% confidence interval, 2.2 to 2.5) for all TLCs less than 2.00 x 10(9)/L, to 33.2 (95% confidence interval, 24.1 to 45.7) for all TLCs less than 1.00 x 10(9)/L. The specificity for this prediction increased from 57% to 97% over this range. The LR also increased from 1.4 (95% confidence interval, 1.3 to 1.6) for all TLCs less than 2.00 x 10(9)/L to 9.7 (95% confidence interval, 7.1 to 13.1) for all TLCs less than 1.00 x 10(9)/L in predicting a CD4+ percentage less than 20%.
Conclusions: The TLC, between 1.00 x 10(9)/L and 2.00 x 10(9)/L, appears to be a useful predictor of significant immunosuppression as measured by a CD4+ T-cell count less than 0.20 x 10(9)/L in HIV-infected persons. The LR for a given TLC value and the pretest probability of immunosuppression can be used to determine the posttest probability of significant immunosuppression in individual patients. For example, in a patient with a TLC less than 1.50 x 10(9)/L and a pretest probability of 16%, the posttest probability of a low CD4+ T-cell count increases to 53%. In contrast, a TLC greater than 2.00 x 10(9)/L in an individual with a pretest probability of 30% will decrease the posttest probability of a low CD4+ T-cell count to less than 4%. Physicians should find these data useful to help predict the risk for opportunistic infection among HIV-infected persons who present with syndromes that are potentially compatible with opportunistic infection but who have not had recent or prior CD4+ T-cell analysis.