Hemoglobin is hemoglobin, and high hemoglobin refers to an increased concentration of hemoglobin in the peripheral blood. In clinical practice, there are two types of increased hemoglobin concentration: first, relative increase; second, absolute increase. Relative increase is common when the body is severely dehydrated, such as after a lot of sweating, severe diarrhea, vomiting, etc., due to the concentration of blood, there will be an increase in hemoglobin. A true increase in hematocrit is often caused by an increase in the number of red blood cells due to various reasons, such as an increase in hemoglobin concentration due to oxygen scarcity in residents of highland areas. Chronic hypoxic diseases such as chronic obstructive pulmonary disease and congenital cyanotic heart disease can also present with increased hematocrit. Patients with true erythrocytosis, a myeloproliferative disorder, can also develop abnormally high hematocrit.