Measurement of ferritin in serum by radioimmunoassay

SUMMARY A method for the measurement of circulating ferritin concentrations by direct radio-immunoassay is presented. The method described is simple to operate, precise, and sensitive and is suitable for the routine diagnostic measurement of ferritin in either plasma or serum. Ferritin is the major intracellular iron storage protein found in the body, consisting of a spherical protein shell of MW 450 000 made up of 24 iden-tical subunits. Iron is stored in the inner core as crystalline ferric-oxide-phosphate. Ferritin is found mainly in the reticuloendothelial system, predomi-nantly in the spleen, liver, and bone marrow. Circulating levels of ferritin have been shown to reflect the total body iron stores in most clinical situations (Walters et al., 1973; Bentley and Williams, 1974) with the exception of familial varieties of haemochromatosis (Wands et al., 1976). A number of sensitive radioisotopic assays have now been described for measuring ferritin in plasma or serum. All have been based on an immuno-radiometric technique in which the antibody to ferritin is labelled with iodine-125 (Addison et al., 1972; Miles et al., 1974; Halliday et al., 1975). The major advantage of this immunoradiometric technique over previously described methods is that it is sensitive enough to measure normal circulating levels of ferritin. Unfortunately, like many immunoradiometric methods, this technique may be time-consuming and imprecise and show inter-assay variation in results. Recent radio-immunoassays have been described for use in man in which ferritin itself was labelled with 125I (Marcus and Zinberg, 1975; Luxton et al., 1977). The present paper confirms and extends the use of direct radioimmunoassays for measuring ferritin in human serum or plasma. This technique is suffic-iently sensitive to detect circulating levels within the normal range, it is easier to perform, and is more reproducible and economical than the im-munoradiometric methods in current use