An increase in which of the following suggests a shortened life span of RBCs and hemolytic anemia?

A rise in the reticulocyte count indicates that the bone marrow is producing more red blood cells in response to anemia or a decrease in red blood cell lifespan, such as in cases of hemolytic anemia. Reticulocytes are immature red blood cells that are released into circulation when the body needs to compensate for a loss of red blood cells due to destruction or other issues.

In hemolytic anemia, the destruction of red blood cells happens at an increased rate, leading to the need for the bone marrow to produce more red blood cells. As the reticulocyte count rises, it reflects an active response by the body to compensate for the shortened lifespan of the red blood cells, thus effectively suggesting that hemolysis is occurring.

While an increase in hemoglobin or hematocrit would typically indicate improved or stable red blood cell levels, they wouldn't directly reflect the body's response to hemolysis. Red cell distribution width measures variability in red blood cell size and doesn't specifically relate to lifespan or hemolysis. Therefore, in the context of identifying a response to shortened RBC lifespan associated with hemolytic anemia, the reticulocyte count is the most indicative measure.