The diagnosis and treatment of iron deficiency is a primary public health goal. This study aimed to make an inventory of the use of biomarkers to assess the iron supply in patients given iron replacement therapy. A retrospective longitudinal real-world study of a cohort of patients receiving iron replacement therapy was conducted using data from healthcare coverage databases between January 2006 and December 2015 in France. The frequency of oral or intravenous iron treatment episodes preceded and/or followed by a biological assessment of iron deficiency was described. We then differentiate patients with or without chronic inflammatory diseases, which could impact the prescription. The evolution between 2006 and 2015 was also studied. The 96,724 patients received an average of 4.9 administrations of iron per patient, corresponding to 1.7 treatment episodes. In one-third of treatment episodes (34.6%), patients had a pre-treatment biological assessment, 15.5% a post-treatment assessment, and 7.3% both. The post-treatment measure of iron supply markers (i.e., Ferritin and transferrin saturation) was more frequent in patients suffering from chronic inflammatory diseases than in those without underlying chronic condition (22.6% to 41.0% vs. 3.1%; p < 0.0001). Serum ferritin was measured 30 times more than transferrin saturation measurements. The use of both tests increased steadily during the study period, although remaining low. Despite the recommendations, biological assessments of iron status are seldom prescribed and/or performed in the context of a pre- or post-treatment assessment, although more frequently realized in patients with chronic inflammatory diseases.