Hemoglobin is a protein that carries oxygen from the lungs to the rest of the body. It is found in red blood cells and is composed of four parts or subunits. Each unit binds to oxygen. The protein is constructed in a way that the more oxygen it binds to, the easier it is to bind to even more oxygen.
The same goes for the reverse function. The more oxygen that is released from the hemoglobin, the easier it is for the remaining oxygen to be released. As a carrier of oxygen, hemoglobin is crucial for human life, and more specifically for the circulatory system. Hemoglobin also carries carbon dioxide, a waste product of metabolism, from the tissues back to the lungs, where it is exhaled.
Normal levels of hemoglobin indicate an effective oxygen transportation and circulatory system without conditions such as blood loss or anemia. Measuring hemoglobin is almost always included in a general blood test or health control test. This is due to the frequent affected values deriving from various conditions.
Hemoglobin is relevant to measure in cases such as blood loss, where red blood cells (thus hemoglobin) are lost, in bone marrow disorders where the production of hemoglobin and red blood cells may be affected or in conditions that destroy the red blood cells.
Measuring hemoglobin can therefore be used to diagnose anemia, assessing the severity of blood loss, screening for blood disorders and monitoring conditions affecting the red blood cells.
High hemoglobin levels, also known as erythocythosis or polycythemia, either indicate that the body is overproducing hemoglobin or red blood cells, or that the hemoglobin and red blood cells are circulating in a reduced blood volume due to dehydration.
Dehydration is the most common cause for elevated hemoglobin levels, and can be caused by for example insufficient fluid intake or diarrhea. Although not a “real” erythrocytosis, it is important to exclude conditions causing an overproduction of red blood cells or hemoglobin, such as the bone marrow disorder polycythemia vera, kidney disease or hormonal imbalances such as testosterone excess.
Other underlying causes may be smoking or chronic hypoxia (often caused by chronic obstructive pulmonary disease (COPD) or high altitudes).
Having high levels of hemoglobin may increase the risk of blood clots, which is why it is important to have a healthcare professional interpret the results with other clinical findings to understand its proper meaning.
Low hemoglobin levels, also known as anemia, indicate that the body is not producing enough red blood cells or hemoglobin, that blood cells are destroyed at a higher pace than produced, that the blood is diluted or that there is a significant blood loss.
Underproduction can be caused by conditions such as deficiency in iron, vitamin B12 or folate. Chronic alcohol consumption can also cause an underproduction. Destruction can be caused by infections or inherited disorders. Dilution is a consequence of fluid retention, often seen in congestive heart failure and liver disease.