Final answer:
Anemia is defined as a decrease in circulating red blood cell mass, leading to lower oxygen delivery to tissues and resulting in symptoms like fatigue.
Step-by-step explanation:
Anemia is a condition characterized by decrease in circulating red blood cell (RBC) mass. This definition corresponds to option 2 in the question provided. Anemia leads to reduced oxygen delivery to the body's tissues, causing symptoms such as fatigue and weakness. There are various types of anemia which can be grouped into three major categories: those caused by blood loss, those due to faulty or decreased RBC production (including sickle cell anemia, iron deficiency anemia, and vitamin deficiency anemia), and those caused by the excessive destruction of RBCs. Common tests for anemia include measuring the size of RBCs with mean corpuscle volume (MCV) and reticulocyte counts to assess RBC production.