Two common schema used to generate differentials for anemia are kinetic and morphologic approaches. Links to both are provided below. The kinetic model uses categories of blood loss, decreased production (hypoproliferative) and increased consumption (hemolysis, decreased RBC lifespan). The morphologic approach is based on the size of red cells: microcytic, normocytic, macrocytic.
Labs to determine etiology of anemia - and common patterns
Common labs (some can be omitted based on suspected etiology): iron, transferrin, transferrin saturation, ferritin, reticulocyte count, peripheral smear, creatinine, lfts, tsh, b12
Reticulocyte count needs adjustment for degree of anemia, as a "normal" absolute retic count in the face of anemia is abnormal (production should be increased). The reticulocyte index (RI) adjusts for the degree of anemia (RI: https://www.mdcalc.com/absolute-reticulocyte-count-reticulocyte-index), w/an RI < 2 indicating hypoproliferation