Anemia is one of the most familiar hematologic conditions. Tests will reveal low red blood cell and hemoglobin values, so what if the red blood cell or hemoglobin values are high? Is it normal? Of course, the answer is not normal! Why is there an increase in red blood cells? Erythrocytosis is often found after routine blood tests, mainly when the red blood cell count exceeds the normal range and/or the hemoglobin concentration exceeds the normal reference range, and the patient also shows a flushed face, or even a flushed, cyanotic face as if after drinking. The phenomenon of increased red blood cells is found to be common in the following situations: 1. To see if the patient is obviously dehydrated at the time of blood collection If there is obvious dehydration and blood concentration, the red blood cell count will increase relatively. 2, to see if there is secondary erythrocyte increase Generally speaking, it is common in chronic and severe lung diseases resulting in long-term chronic hypoxic diseases, such as chronic obstructive pulmonary disease, due to long-term hypoxia, resulting in compensatory erythrocyte increase; there is also a longer period of time living in high altitude areas, due to plateau hypoxia will cause secondary erythrocyte increase. There are also heart disease, renal vascular disease, severe snoring, etc. can lead to secondary erythropoiesis due to hypoxia, while adrenal tumors, kidney tumors, other tumors, etc. can lead to secondary erythropoiesis due to excessive secretion of erythropoietin. 3, to see if it is a true erythropoietic sign This is due to abnormal bone marrow hematopoietic stem cell genes, especially the presence of JAK-2V617F gene mutation, the bone marrow unregulated overproduction of red blood cells, resulting in a sustained and significant increase in peripheral blood erythrocytes, hemoglobin concentration is often greater than 185g/L in men and 165g/L in women, mostly with increased white blood cells and platelets. This is the time to check the bone marrow and the JAK-2V617F gene mutation. True erythrocytosis is a disease with a malignant nature and requires aggressive treatment. Although true erythroblastosis is not common in clinical practice, as the disease progresses, it poses a serious health risk to the patient at a later stage, especially since this disease has a high chance of transforming into acute leukemia and affecting the patient’s normal life expectancy.