Use of combined measures from capillary blood to assess iron deficiency in rural Kenyan children.

Community-based surveys of iron deficiency (ID) require simple, accurate methods that can be used in remote areas. The objective of this study was to assess iron status in rural Kenya using "field-friendly" methods for capillary blood, including an improved dried blood spot assay for transferrin receptor (TfR). A single finger stick was used to obtain capillary blood from 275 school-age children. Whole blood was applied directly to filter paper, dried, and later analyzed for TfR, as well as C-reactive protein (CRP), an acute-phase protein that serves as a general marker of inflammation. Capillary blood was also used to measure hemoglobin (Hb) concentration and the ratio of zinc protoporphyrin to heme (ZPP:H). The Hb concentration alone provides the lowest estimate of the prevalence of ID (8.0%). Because ZPP:H is reported to be elevated in the presence of inflammation, we constructed a preliminary diagnostic model based on elevated ZPP:H and normal CRP level, estimating the prevalence of ID at 25.9%. When TfR is added to a multiple criteria model (elevated ZPP:H in the absence of elevated CRP and/or elevated TfR level) the prevalence of ID is estimated to be 31.2%. This study demonstrates the diagnostic utility of combining TfR with other indexes of iron status, enabling the detection of ID in both the presence and absence of infection. Furthermore, this study is the first field application of TfR blood-spot methods, and it demonstrates their feasibility in remote field settings.