Hemoglobin and iron are the main indicators of anemia. They will also note
the size and shape or the red blood cells. Low iron/hemoglobin results in
smaller, less uniform red blood cells. The first question to answer is "Is
the problem due to loss of blood, or a problem in the production of red
blood cells."

Hope this helps. I'm NOT an MD, but I just went through the exact same
thing.

A "CBC" (complete blood count) generally will include a white blood
cell count, hemoglobin, hematocrit, and platelet count, along with a
differential count of the various types of white blood cells. The CBC
is most typically used to screen for a variety of hematologic disorders
(commonly anemia) and infection. It is not absolutely diagnostic of
anything, really, although in a clinical context, certain things may be
inferred. If a CBC is abnormal in any significant way, follow-up
studies are usually required to narrow down the diagnosis.