The kidney, the congenital base of life, determines the condition of the bone and marrow. In the case of congenital insufficiency or improper postnatal nourishment, the kidney is deficient and the marrow decreases. This will cause failure to produce renal essence and blood, giving rise to aplastic anemia. If the above state lasts for a long time, it will make qi and blood deficient and other viscera involved, resulting in the corresponding symptoms. In short, the disease belongs to asthenia of the spleen and kidney resulting in deficiency of both qi and blood.

In this case, qi deficiency makes qi powerless to defend the body externally; blood deficiency leads to internal generation of heat; asthenia of the spleen makes it impossible to keep blood circulating within blood vessels while asthenia of the kidney brings about the inability of the marrow to produce blood. Besides, either internal injury or fever due to attack by exogenous pathogenic factors can force blood to extravasate from blood vessels. Simultaneously, though bleeding may cause yin depletion, it may also result in deficiency of yang and qi. As a result, the cause and effect circulate, giving rise to the deterioration of disease.