There are two main categories of laboratory methods for identifying iron deficiency : screening measurements that detect iron deficient erythropoiesis (IDE) and definitive measurements that evaluate tissue iron status (Table 5). Newer tests include the percentage of hypochromic erythrocytes, reticulocyte hemoglobin content (CHr), and sTfR. It should be added that a therapeutic trial iron has been proposed as a convenient method to diagnose iron deficiency. This is a reasonable approach in otherwise healthy populations, such as teenage girls and pregnant women, at high risk of deficiency. However, in most clinical settings, it is preferable to make a definitive diagnosis at the outset.