A specialized serum ferritin assay has been developed for the detection of iron deficiency in epidemiologic studies. An enzyme immunoassay (EIA) was employed to eliminate the need for radioisotopes. The problem of low sensitivity inherent with the EIA for serum ferritin was eliminated by the use of monoclonal immunologic reagents. The working range of the assay is 1-100 micrograms/L with a sensitivity of 0.5 micrograms/L. Excellent agreement in serum ferritin levels was observed between the present method and the two-site immunoradiometric assay (IRMA), while the variability at low ferritin concentrations was significantly less with the EIA. Because only 10 microliter of serum is required for each assay, duplicate measurements can be performed on a single capillary tube of blood. When an automatic microtiter plate reader for optical density measurements is used, 80-100 duplicate determinations can be completed by one technologist in a single working day.

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