Anemia means not enough red blood cells (RBCs) in the blood (blood is about 40% RBCs and 60% fluid, called serum or plasma, which includes lots of important proteins, vitamins, etc.). We diagnose Anemia by finding a low amount of hemoglobin. Often, this is due to not enough iron, but not always; various other conditions also cause Anemia (see link to the topic). One is called “Anemia of Chronic Disease” (ACD).
What ACD really means is that the body simply isn’t producing enough RBCs. A RBC only lives 120 days. They’re constantly being produced in the bone marrow, mainly the marrow of our sternum, pelvis, and long bones. There’s plenty of iron, vitamin B12, folic acid, and everything else the body needs to make hemoglobin. But the bone marrow simply slows down (or, very rarely, stops).
ACD can be caused by a wide variety of chronic diseases, like kidney failure, liver failure, heart failure, chronic infections, cancer, rheumatoid arthritis, and much more. It can also be caused by medications and by acute conditions like infection or major trauma; in these cases, the bone marrow starts working fine again once the patient recovers. Giving iron doesn’t help a bit, and will only carry a risk of iron overload (too much iron, which can damage the liver).
Usually the degree of anemia is relatively mild, and a patient has no symptoms. The condition is discovered incidentally, by accident, when doing a complete blood count for other reasons. so treatment is almost never necessary. When the anemia is severe enough to need improvement, there are medications to stimulate the bone marrow, and transfusion is possible. The main issue is how extensively to search for a cause of ACD, when a patient has no obvious medical condition or symptoms. The older the patient and the milder the anemia, the more likely ACD is due to age alone. We may order basic blood tests like a Comprehensive Metabolic Panel; some clinicians also order a sedimentation rate or c-reactive protein (if very high, more work up may be indicated). In terms of searching for undiagnosed cancer, we simply perform tests normally done for the person’s age (Pap test, mammogram, & Colon Cancer screening). We refer younger patients with significant anemia to Hematology, who may obtain a bone marrow biopsy to see how the bone marrow is actually working.