Correlation between total and CD4 lymphocyte counts in HIV infection: Not making the good an enemy of the not so perfect

The aim of this study was to assess the correlation and average cost of total lymphocyte count compared with CD4 count as a broad estimate of immunosuppression in HIV-1 infected individuals. Spearman's partial rank correlation were calculated between total lymphocyte count, absolute CD4 count and CD4 per cent stratified by stage of HIV-1 infection for routinely collected samples. Data were collected prospectively from a T cell-subset register combined with clinical data obtained retrospectively from case notes of HIV-infected patients managed at St Mary's Hospital, London 1982-1991. Costing data were obtained through a survey of the departments of haematology and immunology (1989/90 prices). The correlation between 1534 paired absolute lymphocyte count and CD4 lymphocyte count was found to be high (R=0.76). When analysed by stage of HIV infection, the correlation increased from R=0.64 for asymptomatic patients, to R=0.72 for patients with symptomatic non-AIDS HIV infection and R=0.73 for AIDS patients. Correlations between absolute lymphocyte count and CD4 per cent were considerably weaker: R=0.41 all paired counts; R=0.32 for asymptomatic patients; R=0.25 for symptomatic non-AIDS patients; R=0.32 for AIDS patients. Average cost was pound 8 per full blood count compared with pound 38 per T-cell subset analysis. The high correlation between total and CD4 lymphocyte counts, especially for patients with symptomatic I-W disease, demonstrates the suitability of the use of total lymphocyte count in the absence of CD4 counts. Given the considerably lower prices of total lymphocyte counts compared with T-cell subset analysis, this is particularly relevant for developing countries.