Blood tests are mainly for red blood cells, white blood cells, hemoglobin and platelets. If there is a decrease in red blood cells and a decrease in hemoglobin, anemia is considered; if there is an increase in white blood cells, bacterial infection is considered; a decrease in white blood cells may be due to viral infection; a decrease in platelets requires a clear understanding of what causes the decrease in platelets; if there is a decrease in platelets, white blood cells and red blood cells, a blood count abnormality due to hematologic disease or connective tissue disease is considered. If the platelets, white blood cells and red blood cells are all decreased, it is necessary to consider whether the abnormal blood count is due to hematologic diseases or connective tissue diseases. If there is an increase in eosinophils, parasitic infections or skin diseases should be excluded.