| Ineffective treatment |
| Supplements not given as prescribed (eg, due to intolerance) |
| Dietary changes not made (due to intolerance or nonadherence) |
| Insufficient dose or duration of iron supplements |
| Incorrect diagnosis (ie, other causes of anemia) |
| Thalassemia |
| Anemia of chronic disease |
| Mixed nutritional deficiency (combined deficiencies of iron and vitamin B12 or folate) |
| Gastrointestinal disease causing ongoing blood loss or malabsorption |
| Cow's milk protein colitis |
| Celiac disease |
| Parasitic infection |
| Duodenal ulcer |
| Meckel diverticulum |
| Inflammatory bowel disease |
| Other causes of iron deficiency |
| Pulmonary hemosiderosis |
| Mutations causing defective iron transport (rare) |
