Low plasma viscosity suggests the possibility of blood diseases, liver diseases and certain congenital diseases, and other tests are needed to clarify the specific causes. 1. Various blood diseases: such as coagulation disorders, aplastic anemia, acute leukemia and so on. 2. Liver diseases: liver cirrhosis, liver cancer, etc. 3. Congenital diseases: such as congenital fibrinogen deficiency and congenital immunoglobulin deficiency. The normal value of plasma viscosity is 3.84~5.3 mPa/s for men and 3.39~4.41 mPa/s for women. plasma viscosity is one of the main indicators of blood fluidity, and its value mainly depends on the concentration of plasma proteins, such as fibrinogen and globulin. When plasma viscosity is found to be low, it is necessary to combine it with other tests to clarify the disease, and then treat it according to the physician’s instruction.