Whole Blood Collected on Filter Paper Provides a Minimally Invasive Method for Assessing Human Transferrin Receptor Level

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Abstract
Iron deficiency is the most common micronutrient deficiency worldwide, and transferrin receptor (TfR) level has been identified as an important measure of iron status that is not confounded by inflammation. However, logistical constraints associated with sample collection and processing have limited efforts to measure TfR, particularly at the community level. Standardized filter paper provides a relatively convenient and minimally invasive means for collecting and transporting samples of whole blood from simple finger pricks, and we present results of our validation of an improved method for quantifying TfR in dried blood spots. The method is based on commercially available reagents and uses capillary blood that is applied directly from the finger to filter paper, eliminating the need for premeasurement at the collection site. The blood spot TfR assay is precise and reliable, agrees well with plasma TfR, and can be performed at any facility with a microplate reader and basic laboratory equipment. Concentrations of TfR remain stable for at least 4 wk when blood spots are stored at room temperature, but begin to deteriorate after 3 d of exposure to higher temperatures. The advantages and disadvantages of the blood spot TfR method are discussed, as well as its potential contribution to future field-based studies of iron deficiency.