Tertiary reduction refers to a decrease in the erythroid (red blood cells), megakaryotic (platelets), and granulocytic (white blood cells) lineages together. A trilineage decrease suggests a decrease in all whole blood cells in the peripheral blood and is commonly seen in the following disorders: 1. Aplastic anemia: it is the most common disease with three-system reduction. It is caused by various reasons, such as hematopoietic failure of bone marrow and reduction of whole blood cells, and the cause of the disease is still unclear, which may be related to viral infections, chemical factors, and so on. 2. Paroxysmal sleep hemoglobinuria: typical patients have episodes of hemoglobinuria, hence the name, which can be seen in the reduction of the three systems, myeloproliferative reduction, the patient’s neutrophil alkaline phosphatase staining results are often negative, while aplastic anemia is often positive, which can be used as a reference to differentiate between the two. 3. Hypersplenism: the common clinical manifestations are splenomegaly, one or more kinds of hematopoiesis, and the hematopoiesis can be basically recovered after splenectomy. 4. Myelodysplastic syndrome: some patients with this disease can see a reduction in the three lineages, diagnostic tests can be seen increased expression of related antigens, there may be chromosomal karyotype abnormalities. In addition, acute leukemia, malignant histiocytosis, autoantibody-mediated thrombocytopenia and other diseases can also be seen. It is recommended to consult a doctor when a trilogy reduction is detected to avoid delaying the disease.