My fellow just answered a question I have had for years.

Part of the dogma of evaluating iron deficiency in patients with anemia is that after a transfusion the iron indices are altered. Over and over the question comes up…

How long after a transfusion do you have to wait before checking to see if the patient is iron deficient?

Well Jabri, my current fellow went to the literature and found this reference. It looks like the answer is you should be safe 48 hours after the transfusion. This surprised me, I expected the acute effects of the transfusion to persist longer than that.

Abstract from the paper:

The effect of transfusion of packed red blood cells on serum iron level, total iron-binding capacity, and transferrin saturation was studied. Samples of blood from 37 hemodynamically stable patients were obtained for analysis at various intervals following the transfusion of packed red blood cells. In 10 patients with possible iron deficiency, a significant rise in serum iron level and transferrin saturation occurred during the 24 hours following transfusion, which persisted at a marginally significant level up to 36 hours. In the remaining 27 patients, a significant rise was also noted in serum iron level and transferrin saturation results, but the rise did not persist beyond the 24 hours after transfusion. No change in total iron-binding capacity was noted in either group. These data show that the diagnosis of iron deficiency (based on a transferrin saturation of < 0.16) might be missed if iron studies are performed on patients within 24 hours following packed red blood cell transfusion. Therefore, if serum iron studies are obtained for patients suspected of having iron deficiency anemia, these studies are best done on blood samples obtained before blood transfusion.