The second most common type of anemia (after iron-deficiency anemia) is anemia of chronic disease (ACD). This is a mild to moderate anemia accompanying infections, inflammatory disorders or malignant diseases that persist more than 1-2 months (examples include pulmonary infections endocarditis, rheumatoid arthritis, lupus, carcinoma, lymphoma, and myeloma). It’s characterized by low serum iron, despite lots of macrophage storage iron.
The pathogenesis of this anemia is multifactorial. Part of the problem is related to iron metabolism. For the most part, mucosal cells absorb iron okay, but they don’t release it into plasma (so the iron never makes it into red cell precursors!). Macrophages take up iron okay, but they release it very slowly. All of this is mediated, at least in part, by a substance called hepcidin, which is produced by the liver and released in response to inflammation (which, of course, you see in most chronic diseases).
In addition to the iron metabolism stuff, the red cells in this anemia have a shortened lifespan. The weird thing is that if you put cells from patients with ACD into normal patients, the red cells have a normal lifespan; but if you put cells from a normal patient into a patient with ACD, those red cells will die early! To top it all off, there is an impaired bone marrow response to anemia. There’s not enough iron available to make enough red blood cells; also, there’s not enough erythropoietin around, and bone marrow can’t respond to what little there is. Ugh. You’d think with all that stuff going on, the anemia would be severe – but it generally isn’t. Patients usually have no real symptoms related to the anemia; they have enough trouble with whatever chronic disease they suffer from.
The anemia is normochromic and normocytic, usually. Some cases (about 25%) are microcytic (but MCV rarely gets below 72 fL). There is minimal anisocytosis and poikilocytosis. There’s really not a lot to look at under the microscope!
To make the diagnosis, you need to do iron studies. In ACD, you’ll see the following: • ↓ serum iron • ↓ TIBC (total iron binding capacity) • ↓ transferrin saturation • ↑ ferritin (remember: ferritin is an acute phase reactant! So it’s increased in these patients, because there is chronic inflammation present.) • ↑ bone marrow storage iron
This anemia usually is so mild that treatment is not necessary. The anemia develops during the first 2 months of the chronic disease, and it doesn’t progress thereafter. The important thing to remember is that you need to distinguish it from iron-deficiency anemia (use iron studies for this). You wouldn’t want to mix the two up, because anemia of chronic disease requires no further treatment, whereas a diagnosis of iron-defieciency anemia necessitates a search for possible sites of blood loss.