A high hemoglobin level indicates long-term hypoxia or low blood oxygen levels, explains MedlinePlus. High hemoglobin levels commonly result from severe chronic obstructive pulmonary disease, cor pulmonale or failure of the heart's right side, congenital heart disease, or lung disorders such as pulmonary fibrosis, in which the lungs become scarred or thicker.
Other possible causes of high hemoglobin levels include dehydration and polycythemia vera, which is a rare bone marrow disease leading to an abnormal rise in blood cell count, according to MedlinePlus. Normal hemoglobin levels generally range from 13.8 to 17.2 grams per deciliter in males and 12.1 to 15.1 grams per deciliter in females.
Hemoglobin is an oxygen-carrying protein found in red blood cells, explains MedlinePlus. When a person has very low blood oxygen levels resulting from improper lung or heart function, the body produces a higher number of red blood cells to make up for the insufficient blood oxygen supply, states Mayo Clinic. Patients with a bone marrow dysfunction also experience an increased red blood cell production, leading to high hemoglobin levels.
People who go to high altitudes tend to have higher numbers of red blood cell due to the limited oxygen supply, notes Mayo Clinic. Additionally, those who smoke and take drugs or hormones that trigger red blood cell production are likely to have high hemoglobin levels.