Blood routine is one of the three major clinical tests (blood, urine and stool routine are collectively called the three major routines), and is widely used in clinical practice and is one of the necessary tests for physical examination and hospitalization. Therefore, it is very necessary to be familiar with and understand blood routine. Blood components generally include blood cells (including white blood cells, red blood cells, platelets) and plasma, and blood routine is a test to check the classification and number of peripheral blood cells. The knowledge of leukopenia, erythrocyte reduction (decrease in hemoglobin and erythrocyte pressure volume, i.e. anemia) and thrombocytopenia has been explained in other chapters, and this article mainly focuses on the knowledge of elevated blood cells. After the above errors are excluded, hematocrit should be noted, and peripheral blood cell morphological analysis (manual observation of peripheral blood cells for abnormalities in classification, number and morphology) should be routinely performed to further clarify the situation of elevated blood cells. Elevated leukocytes are usually associated with infections, acute bleeding, inflammatory stimuli, drugs, post-splenectomy, and tumors (including hematologic tumors). Leukocytes in peripheral blood mainly include neutrophils, eosinophils, basophils, lymphocytes, monocytes, etc. The white blood cell count in blood routine is the sum of the above-mentioned cells, therefore, after clarifying the elevated white blood cells, we should further understand which type of cells are mainly elevated (based on the analysis of peripheral blood cell morphology), and then conduct further differential analysis. Hematology-related diseases are mainly hematologic tumors such as leukemia, lymphoma, myeloproliferative neoplasm, plasmacytoma, etc. If abnormal leukocytes are found in peripheral blood cell morphology, hematologic diseases should be considered and further bone marrow aspiration and biopsy should be performed to improve bone marrow cell morphology and bone marrow pathology. Elevated erythrocytes should be analyzed together with hemoglobin/erythrocyte pressure product. If all three are elevated, it is usually associated with hypoxia (e.g. congenital heart disease, cardiopulmonary disease, plateau area, etc.), smoking, drugs (stimulation of bone marrow and/or red lineage hematopoiesis), renal disease (including polycystic kidney, renal tumor, renal artery stenosis, post-transplantation, etc.), liver disease (including hepatitis, cirrhosis, etc.), tumor (including myeloproliferative tumor, etc.), etc. etc.), etc.; if red blood cells are elevated but hemoglobin is normal, we should pay attention to thalassemia, iron deficiency, chronic inflammation, chronic diseases, etc. For hematology-related diseases such as myeloproliferative neoplasms, further improvement of blood gas analysis, erythropoietin, bone marrow cell morphology and bone marrow pathology should be performed. Elevated platelets (thrombocytosis is defined as thrombocytosis when routine platelets are greater than 450*109/L) are generally associated with infection, inflammatory stimulation, bleeding, trauma, surgery (including post-splenectomy), hemolysis, drugs, stress, tumors (including myeloproliferative tumors, etc.), etc. Hematology-related diseases and hematologic tumors, including myeloproliferative tumors, require further improvement of hemolysis-related examinations, bone marrow cell morphology, bone marrow pathology, etc. To sum up, the causes of elevated blood cells are diverse and complex, in short: the first to identify the true and false, and then the blood. That is, firstly, to distinguish whether the elevated blood cells are real, and secondly, to see whether there is a possible blood disease, when the peripheral blood cell morphology has classification, quantity and morphology is obviously abnormal, should pay attention to the possible blood disease, it is recommended to go to the blood specialist for further consultation.