Method to confirm immunosuppression in human patients by measuring lymphocyte activation

Methods for measuring the function of lymphocytes and their responses to mitogens or specific antigens, with or without co-stimulatory agents, is provided. The methods are suitable for measurement of the responses of lymphoid cells when they are a subpopulation of cells, and also for measuring the function of specific subsets of lymphoid cells, each subpopulation or subset of a subpopulation having characteristic determinants on their cell surface. The invention also relates to test kits used in performing such methods. The methods of the invention facilitate screening of complex biological fluids, such as whole blood, by means of incubating a sample of the fluid with a mitogen or antigen, with or without co-stimulatory elements, separating the selected subset of interest, e.g., via affinity separation, and detecting the presence of an internal cellular component, advantageously ATP, that is increased as a result of the response.