[Validity of an ELISA test for CD4+ T lymphocyte count and validity of total lymphocyte count in the assessment of immunodeficiency status in HIV infection].

A newly available commercial ELISA (TRAx CD4, T Cell Diagnostics USA) for enumerating CD4+ T lymphocytes has been evaluated with blood samples of 105 HIV seropositive and 6 seronegative subjects. Results from the flow cytometric analysis were used as reference. The sensitivity and specificity of the ELISA to identify HIV seropositive subjects having less than 200 CD4+ T lymphocytes/microliters were assessed and studied using the ROC curve. The reproducibility of the ELISA test was analyzed on 40 samples. The results of the ELISA correlated well with these of the flow cytometric analysis (r = 0.79, p < 0.001). However, the ELISA test tends to overestimate the true CD4 count in HIV seropositives. This overestimation could not be explained by the aspecific contribution of monocytic CD4. The threshold for identifying HIV seropositive subjects with less than 200 CD4+ T lymphocytes with a maximum sensitivity and specificity was determined with ROC curve and equalled 400 cell equivalents with the ELISA (sensitivity and specificity were equal to 80%) and 1,450 lymphocytes/microliters with the total absolute lymphocyte count (sensitivity and specificity were equal to 75%). Using this curve, a threshold of 300 cell equivalents for the ELISA test and of 1,100 lymphocytes/microliters for the absolute lymphocyte count was shown to maximize the specificity (> 95%) without a significant loss of sensitivity.