Future developments in radioimmunoassay with particular reference to the needs of developing countries

Immunoassay are generally used to measure the number of molecules (or mass) of a single substance of unique chemical structure, and cannot validly be employed to measure mixtures of substances of different structure. Insofar as the antigenic substances present in standards or test samples are molecularly heterogeneous, an immunoassay is invalid; the results it yields do not represent the concentrations of a substance in the sample, and have no universal significance. Many substances of biological interest have been shown to be molecularly heterogeneous. Fundamental problems thus arise in the standardization of immunoassays used for the measurement of the amounts or concentrations of such substances. Turning to assay design, past misunderstandings regarding the concepts of sensitivity and precision have resulted in extensive methodology in the immunoassay field and impeded the development of the ultrasensitive methods required for the detection and/or measurements of many substances, such as viral antigens, of crucial importance to many developing countries. Sensitivity can be increased by the use of labels of much higher specific activity than the commonly used radioisotopes. Simple non-isotopic immunoassay methods permit decentralized immunotesting (e.g. for the diagnosis of infectious diseases, pregnancy testing), and are particularly relevant to the needs of developing countries, although the present cost per test is high. 40 refs, 15 figs, 1 tab