This study uses cross-sectional data from 30 household, population-based nutrition surveys of preschool children aged 6 to 59 months and nonpregnant women aged 15 to 49 years across 25 countries to evaluate the current World Health Organization hemoglobin cutoffs for defining anemia among persons who are apparently healthy, and to assess threshold validity with soluble transferrin receptor, which is a biomarker of tissue iron deficiency and physiological indicator of erythropoiesis.