Rapid One-Step Immunofluorometric Assay for Measuring Soluble Transferrin Receptor in Whole Blood

Iron deficiency is common, and understanding of it is advancing (1). The clinical investigation of body iron metabolism now extends beyond the demonstration of iron deficiency (e.g., by bone marrow examination) and estimation of iron storage status (by, e.g., measurement of serum ferritin). An important aim now is to determine whether a patient would benefit from iron supplementation (2)(3)(4). Soluble transferrin receptor (sTfR) measurements (5)(6)(7)(8)(9)(10)(11)(12)(13)(14) have enabled efficient detection of early iron-deficiency anemia (IDA), the treatment of which is essential, especially during phases of psychomotor development, rapid growth, and pregnancy (15)(16)(17)(18). Furthermore, the distinction between IDA and anemia of chronic disease (ACD) has become less complicated, as has the characterization of functional iron deficiency (FID) in cases of multimorbidity in the elderly or in chronic or persisting inflammatory diseases (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). sTfR is a broadly applicable tool to identify individuals who are likely to benefit from iron supplementation and, consequently, is a candidate for point-of-care (POC) testing. Although most of the above-mentioned conditions are highly relevant in the outpatient setting, the current commercially available sTfR methods are not suitable for extra-laboratory testing, and none use unprocessed whole blood as sample (7)(19)(20). We describe a novel, 5-min POC immunoassay for sTfR based on the all-in-one dry-reagent assay concept (21) and time-resolved fluorescence detection. The assays were performed in individual, assay-specific dry-reagent cups that were prepared similarly to the method described by von Lode et al. (22). In short, the monoclonal anti-sTfR capture antibody (HyTest Ltd.) was biotinylated and bound (200 ng/well) …