My understanding is that ferritin is the primary test used to differentiate a true iron deficiency from anemia of inflammation, but the results are not always clearly interpretable. Ferritin is a protein involved in iron storage. When it is low, it pretty clearly suggests that there are not sufficient stores of iron. Often, if the body is sequestering iron to keep it away from a pathogen (i.e., anemia of inflammation or anemia of chronic disease), ferritin will be normal or even elevated because there is stored iron, but iron levels are low because the body is playing keep away with the bacteria. That said, it remains a judgment call with normal ferritin levels because ferritin levels can be artifactually increased by some other factors without there actually being sufficient iron stores. In other words, you can have a true iron deficiency anemia superimposed on an anemia of inflammation/chronic disease. I think it is important to talk to your doctor(s) about all of your test results and the pros and cons in your case given the GI bleed. While it is generally not ideal to give iron when there is an active infection, it seems that the results of studies regarding iron supplementation and infection risk are actually a bit muddy, and many have concluded that the risk-benefit ratio is likely to be specific to the individual context. I actually had anemia of inflammation and did not treat it (which was appropriate). I later had significant bleeding, developed clear IDA with low ferritin, and I have had iron supplementation. Basically, it seems that, most of the time, for people with chronic infections, it seems to make the most sense not to take iron for a mild anemia with normal ferritin. However, as the situation gets more complicated, the decisions get more complicated as well.

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