Blood viscosity, also known as blood viscosity, is an indicator of blood fluidity, and a blood viscosity of 0.45 is not normal, which is a significant decrease in blood viscosity, as normal adult males have a blood viscosity of 3.84-5.30, and adult females have a blood viscosity of 3.39-4.41. Reduced blood viscosity can be caused by a number of reasons, the most common of which are seen in various types of anemia, severe fibrinogen, and other coagulation factor deficiencies. Severe anemia, including iron deficiency anemia, aplastic anemia, hemolytic anemia, thalassemia, and other types of anemia, to name a few, can lead to a condition where blood viscosity is significantly decreased due to a severe reduction in the number of red blood cells. At the same time, there is a condition called congenital fibrinogen deficiency, which also results in a significant decrease in blood viscosity.