A method of detecting the presence of a functionally inhibitory immunointeractive molecule in a biological sample. Preferably, the immunointeractive molecule is directed to a pathogen derived antigen and, more particularly, a parasite derived antigen and, even more particularly, a Plasmodium drived antigen. The method of the present invention facilitates detection of the presence of functionally inhibitory immunointeractive molecules, both in vitro and in vivo, and is useful for qualitatively and/or quantitatively assessing the immune status of individuals who have been previously infected with a parasite, predicting the immune status of individuals vaccinated with an antigen based vaccine, determining the relative contribution of a specific immunoreactivity of antibody to the total inhibitory antibody elicited by combination vaccines which include two or more antigens, assessing vaccines to determine the efficacy of different forms of an antigen, determining vaccine potency, assessing the protective potential of certain immunoreactivities of antibodies and determining the importance of parasite inhibitory antibodies.