In elderly adults, anemia is common and multifactorial. Inflammation, which is frequently observed in hospitalized elderly patients, profoundly alters iron metabolism, making it difficult to accurately assess true iron status.

The objective of this study is to identify a predictive model that can estimate iron deficiency status in the absence of inflammation using transferrin saturation (TSAT) measured during an inflammatory phase. This model could help distinguish true iron deficiency from anemia of inflammation, improve patient management, and reduce decision-making delays.

The study will be conducted in two distinct phases: a pilot phase involving up to 200 patients at a single center in France, followed by a main phase involving 1,523 patients across multiple centers in France. Participants will be adults aged over 75 years who are hospitalized in a geriatric ward and present with an acute inflammatory episode (C-reactive protein [CRP] > 50 mg/L).

In addition to routine analyses performed during hospitalization, supplementary laboratory analyses will be carried out. Following admission in hospital, patients will receive standard medical care. Upon admission or on the following day, patients, their trusted representative, or relatives will be informed about the study. If eligibility criteria are met, the patient will be enrolled.

Research-specific laboratory analyses will be performed on blood samples collected at 4 times:

• the day after admission;
• when CRP < 20 mg/L (pilot phase only);
• when CRP < 10 mg/L;
• five days after a CRP < 10 mg/L. These additional analyses will not require another blood sample, as they will be performed on samples collected as part of routine clinical care. They constitute the main research specific intervention.