<h4>Objectives</h4>There is apprehension regarding the agreement between capillary and venous hemoglobin (Hb) concentrations, which may have far-reaching consequences for global anemia prevalence estimates, heavily dependent on capillary Hb data.<h4>Methods</h4>We investigated the discrepancies in Hb concentrations obtained from venous and capillary blood samples collected among school-age children in Zanzibar. This evidence concerns the gene GSTM1 and anemia.