Hemoglobin, a protein in red blood cells, plays a central role in oxygen transport. It carries oxygen from the lungs to tissues and returns carbon dioxide for exhalation. Elevated hemoglobin, known as polycythemia, indicates an increased amount of this protein. This can thicken blood, slowing its flow and raising the risk of complications like blood clots.
Primary Bone Marrow Conditions
Elevated hemoglobin levels can stem directly from conditions affecting the bone marrow, the soft tissue inside bones where blood cells are produced. The bone marrow then overproduces red blood cells independently of external stimuli.
A prominent example is Polycythemia Vera (PV), a rare blood cancer. With PV, the bone marrow generates excessive red blood cells, and sometimes white blood cells and platelets. This overproduction is linked to a genetic change, often a JAK2 gene mutation, causing stem cells in the bone marrow to reproduce abnormally. It is considered primary because it originates within the bone marrow, not as a response to another underlying disease.
Conditions Leading to Reduced Oxygen
The body responds to low oxygen levels by increasing red blood cell production to enhance oxygen delivery. This compensation can lead to elevated hemoglobin.
Living at high altitudes, with less oxygen, naturally triggers this response. The body adapts by producing more erythropoietin (EPO), a hormone that stimulates the bone marrow to create additional red blood cells, increasing the blood’s oxygen-carrying capacity.
Chronic lung diseases like Chronic Obstructive Pulmonary Disease (COPD), emphysema, and chronic bronchitis impair the lungs’ ability to absorb oxygen. The resulting chronic low oxygen levels signal the body to produce more red blood cells as compensation.
Sleep apnea, with repeated pauses in breathing during sleep, causes intermittent drops in blood oxygen. These recurring periods of oxygen deprivation stimulate the bone marrow to produce more red blood cells, leading to higher hemoglobin over time.
Certain congenital heart diseases, present from birth, can also result in inefficient oxygen delivery throughout the body. To counteract this, the body increases red blood cell production to meet the oxygen demands of the tissues.
Smoking also contributes to higher hemoglobin levels due to carbon monoxide in cigarette smoke. Carbon monoxide binds to hemoglobin with greater affinity than oxygen, forming carboxyhemoglobin, which reduces blood’s ability to transport oxygen effectively. To compensate for this reduced oxygen-carrying capacity, the body produces more red blood cells, leading to an increase in hemoglobin.
Other Medical Issues and Lifestyle Factors
Beyond primary bone marrow disorders and chronic oxygen deprivation, several other medical conditions and lifestyle choices can contribute to elevated hemoglobin.
Certain kidney conditions can lead to an overproduction of erythropoietin (EPO), the hormone prompting the bone marrow to produce red blood cells. This excessive EPO stimulation results in more red blood cells and, consequently, higher hemoglobin.
Similarly, some tumors, especially those affecting kidneys, liver, or uterine fibroids, can produce EPO, which directly stimulates red blood cell production.
Dehydration can also cause an apparent increase in hemoglobin, though the body isn’t producing more red blood cells. When the body lacks sufficient fluids, blood’s liquid component, plasma, decreases, concentrating existing red blood cells and making hemoglobin appear falsely high. Once rehydrated, these levels typically return to normal.
The misuse of performance-enhancing drugs, like anabolic steroids or synthetic EPO, can also lead to elevated hemoglobin. Anabolic steroids can directly stimulate red blood cell production, while synthetic EPO is a lab-made hormone boosting red blood cell counts, often used by athletes to enhance oxygen delivery. These substances can significantly increase hemoglobin, carrying associated health risks.