A red blood cell (RBC) count measures the number of red blood cells, also known as

erythrocytes, in your blood. Red blood cells carry oxygen from your lungs to every cell in

your body. Your cells need oxygen to grow, reproduce, and stay healthy. An RBC count that

is higher or lower than normal is often the first sign of an illness.A low RBC count, also

known as anemia, can affect the body's ability to transport oxygen and nutrients around the

cardiovascular system. It can cause fatigue, dizziness, and heart palpitations.