What Is an Erythrocyte (RBC)?

What Is an Erythrocyte (RBC)? Short Definition

RBC is the abbreviation of the English phrase "Red Blood Cell" and is called erythrocyte or red blood cell in Turkish. Although in some search queries the letters get mixed up and it is written as "what is rcb", the abbreviation meant is still RBC. The shortest answer to the question of what an erythrocyte (RBC) is: erythrocytes are the most numerous group of cells among the formed elements of the blood; they are produced from stem cells in the bone marrow and have a life cycle lasting an average of 100-120 days. While erythrocytes that complete their lifespan are broken down in the spleen and liver, the bone marrow continuously maintains the production of new erythrocytes.

To approach the question of what erythrocyte means in a somewhat more technical way: these cells are carrier cells that transport the oxygen they take from the lungs to all tissues in the body and carry the carbon dioxide formed in cells back to the lungs. This function is carried out by a protein called hemoglobin found inside erythrocytes. Because hemoglobin has an iron-containing structure, it can bind to oxygen and carbon dioxide. Thanks to their anucleate and biconcave structure (a disc shape that is hollow in the middle with raised edges), erythrocytes can pass easily through small vessels; this shape also increases the surface area of the cell and facilitates gas exchange.

Why Are the Structural Features of Erythrocytes Important?

A mature erythrocyte has no nucleus and lacks most organelles; this leaves more room inside the cell for hemoglobin. The flexible structure of the cell membrane allows erythrocytes to pass through capillaries much narrower than their own diameter by temporarily changing their shape. When this flexibility is impaired (as in some hereditary diseases), erythrocytes may be damaged more easily in small vessels or may be destroyed early. The shape, size and hemoglobin content of erythrocytes are important clues that are examined during a blood test and used in the differential diagnosis of anemia or other blood diseases.

How Does Erythrocyte Production Take Place? (Erythropoiesis)

Erythrocyte production (erythropoiesis) takes place in the bone marrow, and this process is regulated by the hormone erythropoietin (EPO), which is produced in the kidneys. The transformation from a stem cell into a mature erythrocyte passes through several intermediate stages; during this process the cell gradually becomes smaller, accumulates hemoglobin, and in the final stage loses its nucleus and joins the circulation. When the oxygen level in the tissues decreases, the kidneys secrete more erythropoietin, which stimulates the bone marrow to produce more erythrocytes. This regulatory mechanism is important for understanding the causes of high and low RBC; because both lung-heart diseases and kidney-related conditions can affect this cycle and lead to a change in the erythrocyte count. It is known that nutrients such as sufficient iron, vitamin B12 and folate are also necessary for this production process to function in a healthy way.

The Relationship Between Erythrocytes and Blood Group

Some structures (antigens) found on the cell membrane of erythrocytes determine a person's blood group (the A, B, AB, 0 and Rh systems). These antigens are not directly related to the oxygen-carrying function of the erythrocyte; however, they are important for compatibility before a blood transfusion. For this reason, the concept of "erythrocyte" concerns both the numerical value in the complete blood count and blood group compatibility; the two are evaluated for different purposes.

What Is RBC in Blood? Its Place in the Complete Blood Count and Related Parameters

In the complete blood count (hemogram) test, the RBC value is not evaluated alone; it is evaluated together with other parameters such as hemoglobin, hematocrit, MCV (mean corpuscular volume), MCH (mean corpuscular hemoglobin), MCHC (mean corpuscular hemoglobin concentration) and RDW (red cell distribution width). The answer to the question of what RBC is in blood is in fact part of this holistic evaluation; interpreting by looking only at the RBC count can be misleading.

The general meaning of these parameters can be summarized as follows:

For example, even if the RBC count is within the normal range, a microcytic anemia process may be present if the MCV is low, and a macrocytic process may be present if the MCV is high. For this reason, all of the results should be interpreted together by the physician, along with the patient's history and examination findings.

Peripheral Smear and Erythrocyte Morphology

In some cases, the physician may find it appropriate to request a peripheral blood smear in addition to the hemogram result. In this examination, the shape of erythrocytes (poikilocytosis), size variation (anisocytosis) and color intensity are evaluated under the microscope. For example, in iron deficiency erythrocytes may look pale and small, while in some hereditary diseases (such as sickle cell disease and thalassemia) erythrocytes may show typical shape changes. This examination is a complementary method that contributes to differential diagnosis together with RBC and other hemogram parameters.

RBC Should Not Be Confused with Sedimentation (ESR)

Because the word "erythrocyte" appears in both, the RBC count may sometimes be confused with the erythrocyte sedimentation rate (ESR, sedimentation test). While RBC measures the number of erythrocytes in the blood, the sedimentation test is a separate test that measures how much erythrocytes settle in a tube over a certain period and whose value generally increases in the presence of inflammation (an inflammatory process). The two are requested for different purposes and answer different clinical questions; in a test, the RBC may be normal while sedimentation is high, or the opposite may be seen.

How Is RBC Measured? When Is the Test Requested?

The RBC value is measured with the routine complete blood count (hemogram) test. The blood sample is analyzed in a laboratory device and the number of erythrocytes in one microliter (µL) of blood is calculated. This test is generally requested in the following situations:

• General check-ups and periodic health checks
• Routine pre-operative evaluation
• Follow-up of chronic diseases (kidney, heart, lung diseases, etc.)
• Investigation of complaints such as fatigue, palpitations, shortness of breath and dizziness
• Pregnancy follow-up and regular check-ups
• Monitoring of chemotherapy, radiotherapy or treatments that may affect the bone marrow

No special preparation is generally required for the test; however, if other tests are requested together with it, you may be asked to give blood on an empty stomach. In this regard, it is appropriate to follow the guidance of the relevant healthcare institution before blood collection.

What Should the RBC Blood Value Be? What Should the Erythrocyte Count Be?

The erythrocyte count may differ according to age, sex, the altitude of the place of residence, pregnancy status and the laboratory device used. The general reference ranges are approximately as follows:

Because the oxygen pressure in the ambient air is low in people living at high altitude, erythrocyte values may be somewhat higher than at sea level so that the body can adapt to this. This is not a disease but a physiological adaptation response.

There is no single definite answer to the question "what should the RBC be" or "what should the erythrocyte count be"; since each laboratory may have its own reference range depending on its device and method, looking at the "normal range" information stated in the test result provides a more accurate evaluation. Some laboratories may report the RBC value in million/µL, others in 10¹²/L; although the numerical value is the same, the unit notation may differ, so it is recommended to look at the reference range next to the result. The interpretation of the RBC value should be made by the physician together with other parameters such as hemoglobin, hematocrit and MCV. A result being slightly outside the reference range does not always mean a disease on its own; it needs to be evaluated together with repeated measurements and the clinical picture.

What Is High RBC? What Does High Erythrocyte Mean?

High RBC is defined in the medical literature as erythrocytosis or polycythemia. The answer to the question of what high RBC in blood is: the erythrocyte count being measured above the upper reference limit determined by the laboratory. This condition is not a disease on its own but may be a finding of an underlying process.

Erythrocytosis is generally considered in three groups:

• True (absolute) erythrocytosis: Occurs as a result of a real increase in erythrocyte production in the bone marrow; it can be primary (bone marrow-origin, such as polycythemia vera) or secondary (such as a compensatory response to a low oxygen level).
• Relative erythrocytosis: The erythrocyte count has not actually increased; it appears high in the measurement because of a decrease in blood plasma volume. Dehydration is one of the most common causes of this group.
• Secondary erythrocytosis: Develops as a result of the body's response to a low oxygen level or increased erythropoietin release.

What Causes High RBC?

Some conditions in which high erythrocytes (high erythrocytes in blood) can be seen are as follows:

• Living at high altitude: In places where oxygen pressure is low, the body may produce more erythrocytes in order to deliver sufficient oxygen to the tissues.
• Chronic lung or heart diseases: In conditions in which the oxygenation of the blood is reduced, such as COPD, sleep apnea syndrome and some congenital heart diseases, erythrocyte production may increase as compensation (secondary erythrocytosis).
• Kidney-related causes: Some kidney masses or cysts may increase the secretion of erythropoietin, the hormone that stimulates erythrocyte production.
• Polycythemia vera: A bone marrow disease that arises from overactivity of stem cells in the bone marrow and must be followed by a hematology specialist.
• Fluid loss (dehydration): A decrease in blood plasma volume may cause the erythrocyte count to appear high in the measurement even though it has not actually increased (relative polycythemia).
• Smoking: Long-term smoking may affect the erythrocyte count due to chronic impairment of oxygenation.
• Some hormonal conditions and medication use: Certain testosterone/hormone treatments may also affect erythrocyte production; these situations should be evaluated under physician supervision.

Symptoms That May Be Seen in High RBC

High RBC in blood may manifest with symptoms such as headache, dizziness, redness in skin color, itching (especially after a hot shower), high blood pressure, blurred vision and shortness of breath. However, since these symptoms may also be due to many other conditions, physician evaluation is necessary for a definitive diagnosis. It is also possible for people with high erythrocytes to have no symptoms; the finding may be noticed incidentally during a test.

What Is Low RBC? What Does Low Erythrocyte Mean?

Low RBC is evaluated medically within the scope of anemia and indicates the risk that the body cannot carry sufficient oxygen to the tissues. The answer to the question of what low RBC means is: the erythrocyte count being measured below the reference range.

Anemias can be examined roughly in three groups according to erythrocyte size (based on the MCV value): microcytic anemias in which erythrocytes are small (for example, iron deficiency), normocytic anemias in which erythrocytes are of normal size (for example, anemia due to chronic disease, acute blood loss) and macrocytic anemias in which erythrocytes are large (for example, B12/folate deficiency). This classification guides the physician in investigating the underlying cause.

What Causes Low RBC?

The following can be counted among the main causes of low erythrocytes:

• Iron deficiency: Insufficiency of iron, which is necessary for hemoglobin production, is among the most common causes of anemia.
• Vitamin B12 and folate deficiency: By disrupting the maturation process of erythrocytes in the bone marrow, it may lead to a decrease in their numbers.
• Chronic kidney disease: A decrease in the kidneys' production of the hormone erythropoietin may negatively affect erythrocyte production.
• Bone marrow diseases: Conditions such as aplastic anemia and leukemia may reduce the erythrocyte production capacity of the bone marrow.
• Blood loss: Conditions such as surgery, trauma, excessive menstrual bleeding or gastrointestinal bleeding may rapidly reduce the erythrocyte count.
• Hemolytic processes: Some hereditary or acquired diseases that cause erythrocytes to be destroyed earlier than normal may also cause low erythrocytes.
• Chronic diseases and treatments: Chemotherapy, radiotherapy or long-term chronic inflammatory diseases may suppress erythrocyte production.

Depending on low RBC, symptoms such as fatigue, palpitations, shortness of breath, dizziness, paleness of the skin and mucous membranes, brittleness of the nails and difficulty concentrating may be seen. The severity of the symptoms varies according to the degree of anemia and the underlying cause. In people in whom low erythrocytes are detected, investigating the underlying cause is important for appropriate follow-up.

What Does Erythrocyte in Urine Mean?

The question "what is erythrocyte in urine" refers to a different subject from the RBC value in the blood. Erythrocytes are not expected in healthy urine, or a very small amount may be detected on microscopic examination. The presence of erythrocytes in a urine test (hematuria) may be due to many different causes, such as the following:

• Urinary tract infection
• Kidney or urinary tract stones
• Kidney diseases (including glomerular diseases)
• Use of some medications
• Temporary changes after intense physical exercise
• Rarely, structural changes in the urinary tract system

When erythrocytes are detected in urine, whether or not there is visible bleeding, it is recommended to apply to the relevant specialist physician (urology or nephrology) to investigate the cause. A small amount of erythrocytes detected in a single test should not be interpreted without being confirmed by repeated tests.

Evaluation Process in High and Low RBC

When high or low RBC is detected, the approach is based first of all on determining the underlying cause. The physician investigates the cause with the patient's history, physical examination, complete blood count, iron/B12/folate levels, kidney function tests, erythropoietin level measurement if necessary, and imaging methods.

The evaluation approach is shaped entirely according to the underlying cause; for example, iron support is prioritized in a low value due to iron deficiency, while management of the relevant disease is prioritized in a high value due to a chronic disease. In some cases, regulating fluid intake, quitting smoking or periodic follow-up may be considered sufficient, whereas in conditions such as polycythemia vera, a special follow-up plan determined by a hematology specialist may be required. There is no single universal answer to the question "how is high RBC treated"; each case is evaluated according to its own cause and clinical picture. For this reason, it is important for people in whom high or low RBC is detected to consult an internal medicine or hematology specialist instead of interpreting it on their own.

RBC Value in Children and During Pregnancy

In children, RBC reference ranges vary with age; in the newborn period the erythrocyte count generally starts higher than in adults and decreases over time to reach childhood reference values. This difference is related to the adaptation process in the circulatory and respiratory systems after birth and generally balances itself out over time.

During pregnancy, RBC and hemoglobin values may run relatively low due to the increase in blood plasma volume; this is a "dilutional" effect and may not always indicate a true erythrocyte deficiency. On the other hand, true anemia is also a frequently seen condition in pregnancy because of the increased need for iron and folate. For this reason, anemia screening and follow-up in pregnancy should be carried out at regular intervals by the relevant obstetrics and gynecology specialist, and any supplements deemed necessary should be arranged on the physician's recommendation.

When Should You See a Doctor?

If the RBC value in a routine blood test falls outside the reference range, and it is accompanied by symptoms such as persistent fatigue, shortness of breath, a marked change in skin color, dizziness, unexplained weight loss, frequent headaches or blood in the urine, it is appropriate to apply to a healthcare institution without losing time. The physician will evaluate the necessary tests and determine the appropriate follow-up approach.

Frequently Asked Questions

What does RBC mean? RBC is the abbreviation of the English phrase "Red Blood Cell", which means red blood cell (erythrocyte).

What is an erythrocyte? An erythrocyte is the red blood cell produced in the bone marrow that is responsible for transporting oxygen and carbon dioxide in the blood.

What is the RBC blood value? The RBC blood value shows the number of erythrocytes in one microliter of blood and is evaluated together with other parameters such as hemoglobin and hematocrit in the complete blood count test.

What does high RBC mean? High RBC means that the number of erythrocytes in the blood is above the reference range, and it is also called erythrocytosis or polycythemia.

What does low RBC mean? An erythrocyte count below the reference range may indicate that the body's oxygen-carrying capacity has decreased and is evaluated within the scope of anemia.

How is high RBC treated? The approach varies according to the cause of the elevation. For this reason, it is not correct to name a definite treatment method; the evaluation and follow-up must be carried out by a physician.

Is a high erythrocyte result always a serious disease? No. Temporary conditions such as dehydration can also raise the RBC value. Marked and persistent elevations require physician evaluation, but not every elevation indicates a serious disease.

What should be done if erythrocytes are seen in urine? The detection of erythrocytes in urine is not considered normal; it is recommended to apply to a urology or nephrology specialist to investigate its cause.

Can the RBC value alone establish a diagnosis of anemia or polycythemia? No. The RBC value should be evaluated by a physician together with other parameters such as hemoglobin, hematocrit and MCV, and with clinical findings.

Are RBC and the sedimentation (ESR) test the same thing? No. RBC measures the number of erythrocytes in the blood; the sedimentation test measures the rate at which erythrocytes settle over a certain period and is generally evaluated in the presence of inflammation. The two provide different information.

Why is a peripheral smear requested? When a notable change in erythrocyte number or size is detected in the hemogram result, a peripheral smear may be requested in order to examine the shape and structure of erythrocytes under the microscope; this is a complementary method that helps in differential diagnosis.