Red blood cells (RBCs) carry oxygen throughout the body and help transport carbon dioxide. They also help keep the blood’s acidity balanced, which is essential for normal body function.
Changes in red blood cells (erythrocytes) on a complete blood count (CBC) can be caused by conditions such as anemia, bleeding, or cancer. If any abnormalities in red blood cell levels are found, you should consult a hematologist or your primary care provider.
Additional tests, such as vitamin B12 and ferritin blood tests, may be ordered to help identify the cause of these changes and guide the most appropriate treatment.
Main functions
The main functions of red blood cells are:
-
Transporting oxygen from the lungs to the rest of the body, helping cells produce energy
-
Helping transport carbon dioxide in the blood so it can be removed from the body by the lungs
-
Helping balance blood pH by regulating acidity
Oxygen transport inside red blood cells is possible because of hemoglobin, a protein found inside these cells.
Evaluating red blood cells
To evaluate red blood cells, a primary care provider or hematologist may order tests such as a complete blood count (CBC) and a blood smear.
According to the National Heart, Lung, and Blood Institute (NHLBI), a CBC measures several parts of the blood, including red blood cells, and red blood cell levels that are higher or lower than normal may be a sign of anemia.
Together, these tests can show changes in the number, size, shape, and appearance of red blood cells.
What are target cells?
Target cells are red blood cells that have an excess of cell membrane relative to the amount of hemoglobin inside the cell.
This changes how hemoglobin is distributed within the cell, giving it a target-like appearance on a blood smear.
Additional tests
In addition to a CBC or blood smear, the doctor may order other tests, such as vitamin B12, folic acid, and ferritin blood tests. These can help identify the cause of red blood cell changes, especially when anemia is suspected.
Normal red blood cell count
A normal red blood cell count is, on average, 5 million/µL in men and 4.3 million/µL in women.
People who live at high altitudes commonly have higher red blood cell counts. This can be a normal adaptation and is not always considered concerning.
High red blood cell count
Red blood cells are considered high when blood levels are above 5.5 million/µL in men and 4.8 million/µL in women. This condition is called erythrocytosis, or polycythemia in some cases.
Excess red blood cells may be caused by lung, heart, or kidney problems, such as kidney cancer or narrowing of the arteries that supply the kidneys.
It may also occur in people who live at high altitudes or who smoke.
Low red blood cell count
Red blood cells are considered low when blood levels are below 4.5 million/µL in men and 3.8 million/µL in women.
A decrease in red blood cells may be caused by nutrient deficiencies, such as iron or vitamin B12 deficiency, kidney disease, autoimmune diseases, such as systemic lupus erythematosus or rheumatoid arthritis, and blood loss, for example.
In more severe cases, a low red blood cell count may also be a sign of cancer. For this reason, it is always important to consult a healthcare provider.