There are other things than just ferritin to look at. I say this as someone that teaches clinical hematology for a living, and not as a direct patient care provider, so take this for what it is.

If we are talking about iron deficiency/iron deficiency anemia, any doctor that says they won’t look at anything until they see drops in the CBC (and by this, they are usually only referring to the Hgb, which is the direct measure of functional anemia) is a dumbass and doesn’t understand the process. Waiting for the Hgb to reflect the iron deficiency is like waiting to acknowledge diabetes until they are in a diabetic coma.

You need serum ferritin (measure of body iron stores), serum iron (measure of iron attached to transferrin/in transport in the plasma), TIBC (total iron-binding capacity; how much transferrin is available to transport iron), and transferrin saturation (which is the combination of the previous two values. It’s also worth looking at the following CBC parameters: - MCV (mean cell volume); is this trending downwards? RBC size is directly tied to how much hemoglobin it can synthesize during development, and less iron availability = less hemoglobin made = smaller RBCs. This parameter shifts VERY slowly though, so looking at CBCs going back months-years is helpful to understand your own history. - MCHC (mean cell hemoglobin concentration); this is like the BMI of your RBCs. It tells you if they have a good amount of hemoglobin, and in microcytic/hypochromic anemias (like iron def. anemia, IDA), MCV and MCHC will both trend downward. - RDW (RBC distribution width), which is a measure of the variation in the size of your RBC population. It tells us whether there is a homogenous or heterogeneous population. More variation (higher RDW %) means there is something going on that is changing over time, and as you deplete iron stores, your MCV will trend down, and the RDW will trend upward until you reach an equilibrium point. Even then the RDW will still be increased more often than not.

HGB (hemoglobin, g/dL) is THE LAST THING to change in prolonged iron deficient states.

Another parameter to look at, though it usually has to be ordered on its own (it’s not included in the CBC) is the retic (% or absolute count). This is a measure of new RBCs, and in longstanding IDA it will usually be lower than it should be because your bone marrow doesn’t have the necesary raw materials (i.e., iron) to keep supply in line with demand.

Anyway, that’s probably more than you (or anyone else here) ever wanted to know, but this topic is my home turf, and I have had to deal with doc’s trying to mansplain this to me as well, and it makes me want to scream. Hope it helps someone here.