This test counts the number of erythrocytes, also referred to as red blood cells (RBC), in the blood. Hemoglobin, a protein that delivers oxygen to the body's tissues, is a component of red blood cells (RBCs), which are created in the bone marrow. This test is frequently performed as part of a complete blood count for a standard physical examination and is primarily used for the diagnosis of anaemia. Fatigue, shortness of breath, lightheadedness when changing positions fast, elevated heart rate, headache, and pale skin are symptoms of a low RBC count. While signs of a high RBC count include weariness, shortness of breath, joint pain, tenderness in the palms and soles, itchy skin, and disturbed sleep.