The causes of high hemoglobin of 187g/L include relative increase of hemoglobin and absolute increase of hemoglobin. 1. Relative increase: It refers to the relative increase of red blood cell volume due to the decrease of plasma volume, resulting in the increase of hemoglobin. This condition can be seen in profuse sweating, severe vomiting, diarrhea, extensive burns, hyperthyroidism crisis and so on. 2. Absolute increase: including true erythrocytosis, certain erythropoietin compensatory increase, such as plateau residents, obstructive pulmonary disease, congenital heart disease and so on. In addition, certain tumors can also cause non-compensatory increase in erythropoietin, resulting in high hemoglobin, such as renal cancer and ovarian cancer. A variety of reasons may lead to high hemoglobin, therefore, when the report suggests that the hemoglobin is high at 187g/L, you should promptly ask your doctor whether you need to do further examination to clarify the cause of the disease and receive appropriate treatment under the guidance of your physician to avoid delaying your condition.