Sources and pathways by which low-grade inflammation contributes to anaemia in rural African children from 6 months to 3 years of age: study protocol for observational studies IDeA 1 and IDeA 2

Background Recent work suggests that persistent inflammation, even at low levels, could be more important than low dietary iron intake in the aetiology of iron deficiency and iron deficiency anaemia (IDA) in young children living in poor environments. Methods We will conduct 2 parallel observational studies in well and unwell rural Gambian children to identify the origins of chronic low-grade inflammation and characterise its relationship to iron handling and iron deficiency anaemia. IDeA Study 1 will enrol 120 well children attending our regular paediatric well-child clinics at 6, 12 and 18 months of age. IDeA Study 2 will enrol 200 sick children suffering from upper-respiratory tract infection, lower respiratory tract infection, gastroenteritis or urinary tract infection and study them on Days 0, 3, 7 and 14 after initial presentation. At each visit, children will be assessed for signs of inflammation. Full blood count and iron-related biomarkers (serum ferritin, serum iron, unsaturated iron-binding capacity, soluble transferrin receptor, transferrin) will be measured before and after an oral dose of ferrous iron to assess status and acute iron absorption. Inflammatory markers (C-reactive protein and α 1-acid glycoprotein), hepcidin, erythroferrone and erythropoietin will be measured to characterize the anaemia of inflammation in these children. Conclusion We will assess the impact of acute and chronic low-grade inflammation on iron absorption and investigate the hypothesis that chronic inflammation, juxtaposed on a poor diet, causes a complex anaemia of inflammation which exacerbates iron deficiency by blocking both non-haem iron absorption and iron utilization by the bone marrow. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research is undertaken with a research grant provided by the Medical Research Council (MR/R023360/1) with additional core funding to the MRC Unit The Gambia @ LSHTM from the UK Medical Research Council (MRC) and the UK Department for International Development (DFID) under the MRC/DFID Concordat agreement. The funding agencies had no role in the design and conduct of the study, and will not have any role in the collection, management, analyses or interpretation of the data nor in the preparation, review, or approval of the manuscript. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: These studies have been ethically approved by The Gambia Government/Medical Research Council Joint Ethics Committee. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors * AGP : alpha-1-acid-glycoprotein CRP : C-reactive protein ELISA : enzyme-linked immunosorbent assay EndoCAB : serum endotoxin core antibody EPO : erythropoietin ERFE : erythroferrone Hb : haemoglobin ID : iron deficiency IDA : iron deficiency anaemia iFABP : enterocyte fatty acid binding protein IL-6 : interleukin 6 IRIDA : iron refractory iron deficiency anaemia LMIC : lower middle income country MCV : mean cell volume REG1b : regenerating protein 1 beta RPI : retriculocyte production index ROC AUC : area under the receiver operating characteristic curve sTfR : soluble transferrin receptor UIBC : unsaturated iron-binding capacity WHO : World Health Organisation.