Formed elements—erythrocytes (red blood cells, or RBCs), leukocytes (white blood cells), and platelets—constitute approximately 45% of the total blood volume. The fluid portion, plasma, is about 90% water. The remaining 10% of the plasma consists of proteins (albumin, globulin, fibrinogen, and enzymes), lipids, carbohydrates, hormones, vitamins, and salts. If a blood specimen is allowed to clot, the fibrinogen is consumed, and the resultant fluid portion is called serum.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.