Diagnostic workup preceding the recognition of unexplained refractory IDA. Diagnostic workup preceding the recognition of subjects with unexplained refractory IDA: in men and postmenopausal women detailed gastrointestinal studies are mandatory. By contrast, in patients with increased physiological needs and in the majority of low-risk patients such as women of child-bearing age, endoscopic gastrointestinal studies preceding oral iron treatment are rarely necessary. The limitations of this diagnostic approach are that (1) complete gastrointestinal workup fails to identify the cause of IDA in a substantial proportion of subjects and (2) such patients, and patients in whom IDA was assumed to be physiological, may be refractory to oral iron therapy. CHr, reticulocyte Hb content; sTfR, soluble transferrin receptor; Tf, transferrin; ZPP, zinc protoporphyrin.