Performance Value of Research of Occult Gastrointestinal Bleeding by Immunoassay in the Diagnostic Process of Iron Deficiency Anemia in Patients Over 75 Years

Immunological testing will be performed systematically for each patient.

Research of blood in fecal sample will be based on 2 methods: one based on a qualitative immunochromatographic method (such as HemSign4 technique, Servibio, France; or all other techniques used at AP-HP) and another quantitative immunoturbidimetric method (OC-Sensor, Eiken, Japan). They will be performed systematically with two fresh fecal samples for each patient, before coloscopy examination.

Treating physicians will not be provided with the testing result. The diagnosis of reference will be established by experts based on the result of explorations (colonoscopy, coloscanner) and the patient's progression, blinded to the result of immunoassay.

The intrinsic characteristics of the immunoassay (sensitivity, specificity...) will be determined with reference to this reference diagnosis, using a positivity threshold defined using expert consensus on the weights to be allocated to potential errors.

2 modeling scenarios (without vs with immunological testing) using decision trees based on prevalence and diagnostic performance observed and stochastic simulations.

Inclusion criteria

• Physical status score 3 or 4, aged 75 and older patient, (patients under guardianship may be included).
• Iron deficiency anemia (Hb≤120 g/l for a woman or Hb≤130 g/l for a man), and nonregenerative anemia with reticulocytes <120 000/mm3.
• Patient who has indication for colonoscopy and / or colonography examination, whatever the results of gastroscopy if performed.
• Have a health insurance.
• Informed consent signed.

Exclusion criteria

• Hematemesis or melena
• Life expectancy inferior to 12 months
• Patient has difficulty in follow-up of study.