Acute: Hb and HCt are initially normal, as whole blood (including plasma) is lost.
Subacute (hours): the body (or doctors) replaces lost plasma, causing ↓ hematocrit. There is relative ↓ RBCs as erythropoiesis takes a week, giving what appears to be normocytic anemia.
Compensated: as erythropoiesis kicks in, there is ↑ reticulocytes, reflecting normal marrow response to anemia. Without further blood loss, the normocytic anemia will correct itself.
Chronic blood loss more commonly presents as iron-deficiency anemia than as ↑ RBC production. Reticulocytes ↓, reflecting inadequate erythropoietic factors. This should prompt a search for a cause –occult blood loss in an elderly patient may be the first presentation of colon cancer.