Background: Iron deficiency is assumed to be the major cause of anemia in northeast Thailand, but other factors may be involved.
Objective: We determined the prevalence of anemia among schoolchildren in northeast Thailand and the role of hemoglobinopathies, selected micronutrient deficiencies, and other factors in hemoglobin status.
Design: Blood samples were collected from 567 children aged 6–12.9 y attending 10 primary schools for the determination of a complete blood count and hemoglobin type [Hb AA (normal hemoglobin), Hb AE (heterozygous for Hb type E), and Hb EE (homozygous for Hb type E)] and the measurement of serum ferritin, transferrin receptor, retinol, vitamin B-12, and plasma and erythrocyte folate concentrations. Children with a C-reactive protein concentration 
10 mg/L (n = 12), which indicated infection, were excluded.
Results: The prevalence of anemia was 31%. Age, hemoglobin type, and serum retinol were the major predictors of hemoglobin concentration. Hb AA and Hb AE children with anemia had lower (P < 0.01) hematocrit, mean cell volume, and serum retinol values than did their nonanemic counterparts; no significant differences in serum ferritin were found by hemoglobin type. Only 16% (n = 22) of the anemic Hb AA and Hb AE children were iron deficient. Hb AA and Hb AE children with a serum retinol concentration <0.70 µmol/L (n = 14) had a significantly higher geometric mean serum ferritin concentration than did those with a retinol concentration 0.70 µmol/L (P = 0.009); no significant difference in transferrin receptor concentrations was found between these 2 groups.
Conclusions: Hemoglobinopathies, suboptimal vitamin A status, and age were the major predictors of hemoglobin concentration. The contribution of iron deficiency to anemia was low, and its detection was complicated by coexisting suboptimal vitamin A status.