The present invention involves the reaction of a CD4 immuno-conjugate with a sample of patient whole blood. The CD4 immuno-conjugate consists of one or more antibodies with specificity for the CD4 surface receptor coupled to a signal moiety, or “label”, that is detectable by a flow cytometer. Such labels may generate a signal by such means as fluorescence properties, light scatter properties, electronic properties, or magnetic properties. The CD4 immuno-conjugate binds to both the CD4 positive lymphocytes (Helper T cells) and all monocytes. Differential detection means are employed to count immuno-conjugate labeled Helper T cells. The present invention distinguishes itself by simultaneously measuring the signal level from monocytes as a means to verify sufficient activity of the anti-CD4 antibody.
